Student’s Manual For Level One and Two in Agriculture 1

National Institute of Education

Ministry of Education, Maldives, 2021

(Final Draft Document)

Prepared By:

Abdulla Ibrahim,

Santhosh. M

School TVET Unit, Educational Development Centre,

for Centre for Continuing Education, 2010

STUDENT MANUAL FOR

Agriculture Level One and Two

Student’s Manual For Level One and Two in Agriculture 2

Table of Contents: Module 1: Introduction to Agriculture ……………………………………… Page 3 - 10

Module 2: Weather and crops ………………………………………………. Page 11-27

Module 3: Soil ………………………………………………………………. Page 28-32

Module 4: Water ……………………………………………………............... Page 33-45

Module 5: Land Utilization …………………………………………............... Page 46-50

Module 6: Soil and Water Conservation …………………………………….. Page 51-61

Module 7: Soil Fertility and Plant Nutrients ………………………………… Page 62-70

Module 8: Management of Soil Fertility …………………………………….. Page 71-73

Module 9.1: Fertilizers ………………………………………………………... Page 74-78

Module 9.2: Deficiency symptoms of Macro and Micro Nutrients …………… Page 79-81

Module 9.3: Nitrogen ………………………………………………………… Page 82-85

Module 10.1: Methods of Cultivation ……………………………………………… Page 86-90

Module 10.2: Present Cropping Patterns and Uses …………………………….. Page 91-95

Module 11: Weed Control …………………………………………………... Page 96-106

Module 12.1: Identification of Weed and Uses of Organic Pest ……………….. Page 107-114

Module 12.2: Pest Management ……………………………………………….. Page 115-121

Module 12.3: Pesticides ……………………………………………………….. Page 122-127

Module 12.4: Using methods of Pesticides ……………………………………. Page 128-139

Module 13.1: Diseases of Crops ………………………………………………. Page 140-147

Module 13.1: Fungicides ……………………………………………………… Page 148-156

Module 14: Project I

Student’s Manual For Level One and Two in Agriculture 3

Module 1

Introduction to Agriculture

Introduction

Agriculture is the production of food and goods through farming. Agriculture was the key

development that led to the rise of human civilization with the husbandry of domesticated animal

and plants (i.e. crops) creating food surpluses that enabled the development of more densely

populated and stratified societies. The study of agriculture is known as agricultural science Central to

human society, agriculture is also observed in certain species of ant and termite.

Agriculture encompasses a wide variety of specialties and techniques, including ways to expand the

lands suitable for plant rising, by digging water-channels and other forms of irrigation. Cultivation of

crops on arable and the pastoral heading of livestock on rangeland remain at the foundation of

agriculture. In the past century there has been increasing concern to identify and quantify various

forms of agriculture. In the developed world the range usually extends between sustainable

agriculture (e.g. Organic agriculture) and intensive farming (e.g. industrial agriculture).

Modern agronamy, plant breeding, pesticide and fertilizers and technological improvements have

sharply increased yields from cultivation, and at the same time have caused widespread ecological

damage and negative human health effects. Selective breeding and modern practices in animal

husbandry such as intensive (and similar practices applied to the chicken) have similarly increased

the output of meat but have raised concerns about animal cruelty and the health effects of the

antibiotics, growth hormones and other chemicals commonly used in industrial meat production.

The major agricultural products can be broadly grouped into foods, fibers, fuels and raw materials.

In the 2000s, plants have been used to grow biofuels, biopharmaceuticals, bioplastics, biofuels and

pharmaceuticals Specific foods include cereals, vegetables, fruits and meat fibers include cotton,

wool, hemp, silk, and cotton raw materials flax include lumber and bamboo. Other useful materials

are produced by plants, such as resins, Biofuels include methane from biomas, ethanol and biodiesel

cut flowers nursery plants tropical fish and birds for the pet trade are some of the ornamental

products.

Student’s Manual For Level One and Two in Agriculture 4

Agriculture in Maldives

The Maldives is an archipelago of 1,190 Indian Ocean islands west of India spanning over

900 kilometers north to south. The total land area is less than 300 square kilometers. The estimated

population in the Maldives is about 300,000 residing on198 inhabited islands. Of these islands, only

33 have a land area greater than one square kilometer. One third of the inhabited islands have a

population of less than 500. An estimated 70 percent of the inhabited islands have a population of

less than 1,000. The population density in the country is 977 per square kilometer; one of the highest

in the world.

At the same time, the country’s narrow economic base needs to be expanded, particularly

agriculture, which presently accounts for less than 3 percent of GDP. Most of the domestic

agriculture demand is met through imports: the ratio of food imports to domestic food production

is 10:1. While some islands contain sufficient soil and water conditions to support increased

agricultural production for certain horticultural products, fishing is still seen as the traditional

livelihood opportunity. The absence of a vibrant private land market limits the access to finance by

prospective farmers. Transport and logistical issues also affect the supply of competitively priced

inputs to agricultural islands, as well as the supply of high quality produce to the capital of Male and

the major tourism islands; much as 25 percent of perishable production can spoil before reaching

Male.

Other economic sectors: The production and the productivity of many horticultural crops

(vegetables and fruits) and Maldives fish can be greatly increased. There are two major potential

markets for horticultural products that have not been fully exploited by local producers. The first

market is the 87 tourist islands with about 650,000 visitors annually. The second market is the local

supermarkets in the capital city of Male’. Key initiatives that need to be addressed include

Student’s Manual For Level One and Two in Agriculture 5

identification of new products and technologies to stimulate increased productivity, better delivery

of support services and market information, and access to credit.

Cereals and Pulses

Nutrient Composition of Some Cereals and Pulses

INTRODUCTION

The great variety of national dishes and dietary patterns that have sustained diverse

populations throughout the world and over many years, clearly indicates that different combinations

of food can lead to good nutritional status. These combinations may include foods from different

groups like cereals and pulses, fruits and vegetables, milk and milk products, nuts and oilseeds, meat,

fish and poultry etc.

However, cereals and pulses play a predominant role in diets of developing countries.

Cereals are the cheapest sources of food energy and contribute a high percentage of calories and

proteins in the diets of people. Pulses are considered as poor man’s meat due to their high protein

content ranging from 20 to 40% and this makes them important in human food from nutrition

point of view Various types of cereals ready to prepare and ready to eat snacks are a part of daily and

festival foods Some of these products are unique due to the use of glutinous rice and typical

processing methods.

But a make a better choice, a good knowledge of the nutritional value of individual foods, as well as

of meals and dishes locally available is of utmost importance.

Oil seeds

Oils are lipid materials derived from plants. Physically, oils are liquid at room temperature

and fats are solid. Chemically, both fats and oils are composed of triglycerides as contrasted with

waxes which lack glycerin in their structure. Although many different parts of plants may yield oil, in

commercial practice, oil is extracted primarily from seeds. Vegetable fats and oils may be edible or

inedible. Examples of inedible vegetable fats and oils include processed linseed oil, tung oil and

caster oil used in lubricants, paints, cosmetics, pharmaceuticals, and other industrial purposes.

Student’s Manual For Level One and Two in Agriculture 6

Oilseed Crops are grown primarily for the oil contained in the seeds. The oil content of small grains

(e.g., wheat) is only 1-2%; that of oilseeds ranges from about 20% for soyabeans to over 40% for

sunflower and rapeseed (canola). The major world sources of edible seed oils are soybeans,

sunflowers, rapeseed, cotton and peanuts. Seed oils from linseed and castor beans are used for

industrial purposes. Edible fats and oils are similar in molecular structure; however, fats are solid at

room temperature, while oils are liquid.

Fats and oils are essential nutrients, comprising about 40% of the calories in the diet. Edible

vegetable oils are used as salad or cooking oils, or may be solidified by a process called

hydrogenation to make margarine and shortening.

While there are many uses for industrial vegetable oils, total world production is only about 3% of

that of edible oils. Industrial applications are based on the properties of particular fatty-acid

components of these oils. For example, flaxseed oil, rich in the unsaturated fatty acid linolenic, is a

drying oil and is used in protective coatings (eg, paints, varnishes). Vegetable oils are used in putty,

printing inks, erasers, coating or core oils, greases, plastics, etc. Oilseed meals from soybeans,

peanuts, rapeseed and flaxseed are rich in protein; mixed with other ingredients (eg, cereal grains),

they provide nutritionally balanced feeds.

Fiber, Millets and Fodder

The millets are a group of small-seeded species of cereal crops or grains, widely grown

around the world for food and fodder they do not form a taxonomic group, but rather a functional

or agronomic one. Their essential similarities are that they are small-seeded grasses grown in difficult

production environments such as those at risk of drought. They have been in cultivation in East

Asia for the last 10,000 years

The protein content in millet is very close to that of wheat both provide about 11% protein by

weight.

Millets are rich in B vitamins, especially niacin B6 and folic acid, calcium, ion, pottasium, magnecium

and zinc. Millets contain no gluten so they are not suitable for raised bread. When combined with

wheat they can be used for raised bread. Alone, they are suited for flat bread.

As none of the millets are closely related to wheat, they are appropriate foods for those with other

forms of allergies/intolerance of wheat. However, millets are also a mild thyroid peroxides inhibitor

and probably should not be consumed in great quantities by those with thyroid disease.

Fodder

The dominant variable on any livestock farm is the supply of feed. Frequently, because of

poor planning aggravated by inefficient production practices and adverse weather conditions, basic

Student’s Manual For Level One and Two in Agriculture 7

feed supplies are erratic and inadequate. It is not economic to plug these gaps with concentrates.

With the price ratio of milk: concentrate currently near 1:1, it is more important than ever to realize

that concentrates are supplementary feeds and not staples. A constant supply of roughage of good

quality is the solid foundation of profitable dairy farming. This leaflet on fodder production planning

is based on a larger publication `Fodder Production Planning' by Jones, Arnott & Klug (1987).

Fodder includes grazing, hay, silage, and roots. The objective of fodder production planning is to

match the production capabilities of the farm with the animals' requirements in order to obtain the

greatest margin over feed costs, within safe limits of natural resource utilization. The carrying

capacity of the property, not the owner's target income, must determine the size of the herd:

specifically, how much suitable fodder can be produced annually for the use of the dairy herd. The

annual fodder requirements of every 100 cows and their associated replacement heifers must be

known. From this total requirement, and from the assessment of the farm's fodder production

capacity, the potential herd size can be calculated. It is neither profitable nor wise to exceed that

herd size. This system ensures green fodder throughout the year the growing of legumes enriches

the soil Green fodder in the first cut is increased up to 50%.

Vegetables

Eating vegetables is one of the tried and true recommendations for a healthy diet and for

good reason. Eating plenty of fruits and vegetables can help you ward off heart disease and stroke,

control blood pressure and cholesterol, prevent some types of cancer, avoid a painful intestinal

ailment called diverticulitis, and guard against cataract and macular degeneration, two common

causes of vision loss.

Student’s Manual For Level One and Two in Agriculture 8

The green color of leafy vegetables is due to the presence of the green pigment chlorophyll is

affected by pH and changes to olive green in acid conditions, and bright green in alkaline conditions.

Some of the acids are released in steam during cooking particularly if cooked without a cover.

The yellow/orange colors of fruits and vegetables are due to the presence of carotenoids which are

also affected by normal cooking processes or changes in pH

The red/blue coloring of some fruits and vegetables are due to anthocyanins which are sensitive to

changes in pH. When pH is neutral, the pigments are purples when acidic, red, and when alkaline,

blue. These pigments are very water soluble

Fruits

In broad terms, a fruit is a structure of a plant that contains its seeds

The term has different meanings dependent on context. In non-technical usage, such as food

preparation, fruit normally means the fleshy seed-associated structures of certain plants that are

sweet and edible in the raw state, such as apples, orange, grapes, strawberries and bananas, or the

similar-looking structures in other plants, even if they are non-edible or non-sweet in the raw state,

such as lemon and olives. Seed-associated structures that do not fit these informal criteria are usually

called by other names, such as vegetables, pods, nut, and cones,

Fruits (in either sense of the word) are the means by which many plants disseminate seeds Most

edible fruits, in particular, were evolved by plants in order to exploit animals as a means for seed

dispersal and many animals (including humans to some extent) have become dependent on fruits as

a source of food. Fruits account for a substantial fraction of world's agriculture output, and some

have acquired extensive cultural and symbolic meanings

Plantation

Student’s Manual For Level One and Two in Agriculture 9

Industrial plantations are established to produce a high volume of wood in a short period of

time. Plantations are grown by state forestry authorities and the paper and wood industries and other

private landowners. Christmas trees are often grown on plantations as well. In southern and

southeastern Asia, rubber, oil palm and more recently teak plantations have replaced the natural

forest.

Industrial plantations are actively managed for the commercial production of forest products.

Industrial plantations are usually large-scale. Individual blocks are usually even-aged and often

consist of just one or two species. These species can be exotic or indigenous. The plants used for the

plantation are often genetically improved for desired traits such as growth and resistance to pests

and diseases in general and specific traits, for example in the case of timber species, volumic wood

production and stem straightness. Forest genetic resources Forest are the basis for genetic

improvement. Selected individuals grown in seed orchard are a good source for seeds to develop

adequate planting material.

In the first year, the ground is prepared usually by some combination of burning, herbicide

spraying, and/or cultivation and then saplings are planted by human crew or by machine.

The saplings are usually obtained in bulk from industrial nurseries, which may specialize in

selective breeding in order to produce fast growing disease- and pest-resistant strains.

In the first few years until the canopy closes, the saplings are looked after, and may be

dusted or sprayed with fertilizers or pesticides until established.

After the canopy closes, with the tree crowns touching each other, the plantation is

becoming dense and crowded, and tree growth is slowing due to competition. This stage is

termed 'pole stage'. When competition becomes too intense it is time to thin out the section.

There are several methods for thinning but where topography permits, the most popular is

'row-thinning', where every third or fourth or fifth row of trees is removed, usually with a

harvester. Many trees are removed leaving regular clear lanes through the section so that the

remaining trees have room to expand again. The removed trees are delimbed forwarded to

the forest road, loaded onto trucks, and sent to a mill. A typical pole stage plantation tree is

7-30 cm in diameter at breast height (dbh). Such trees are sometimes not suitable for timber

but are used as pulp for paper and particleboard as chips for oriented strand board.

As the trees grow and become dense and crowded again, the thinning process is repeated.

Depending on growth rate and species, trees at this age may be large enough for timber

milling; if not, they are again used as pulp and chips.

Around year 10-60 the plantation is now mature and (in economic terms) is falling off the

back side of its growth curve. That is to say, it is passing the point of maximum wood

growth per hectare per year, and so is ready for the final harvest. All remaining trees are

felled, delimbed, and taken to be processed.

The ground is cleared, and the cycle is repeated.

Student’s Manual For Level One and Two in Agriculture 10

Spices

A spice is a dried seed, fruit, root, bark, leaf or vegetative substance used in nutritionally

insignificant quantities as a food additive for the purpose of flavor, colour , or as a preservative that

kills harmful bacteria or prevents their growth.

Many of these substances are also used for other purposes, such as medicine, cosmetics, perfumery

or eating as vegetables. For example, turmeric is also used as a preservative, medicine, garlic, as

vegetables. In some cases they are referred to by different terms.

In the kitchen, spices are distinguished from herbs which are leafy, green plant parts used for

flavorings purposes. Herbs such as basil may be used fresh, and are commonly chopped into smaller

pieces. Spices, however, are dried and often ground or grated into a powder Small seeds, such as

fennel and mustard seeds, are used both whole and in powder form.

Student’s Manual For Level One and Two in Agriculture 11

Module 2

Weather and crops

Weather is a set of all the phenomena occurring in a given atmosphere at a given time. Most

weather phenomena occur in the troposphere, just below the stratosphere. Weather refers generally

to day-to-day temperature and precipitation activity, whereas climate is the term for the average

atmospheric conditions over longer periods of time.

Typical weather stations have the following instruments:

Thermometer for measuring temperature

Barometer for measuring barometric pressure/air pressure

Hygrometer for measuring humidity

Student’s Manual For Level One and Two in Agriculture 12

Anemometer for measuring wind speed

Wind vane for measuring wind direction

Rain gauge for measuring precipitation

Transmissometer for measuring visibility

Ceiling projector for measuring cloud ceiling

Student’s Manual For Level One and Two in Agriculture 13

Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind,

rainfall, atmospheric particle count and numerous other meteorological elements in a given

region over long periods of time. Climate can be contrasted to weather, which is the present

condition of these same elements over periods up to two weeks.

Temperature The amount of heat or cold measured on a thermometer

Humidity is the amount of water vapor in the air

Atmospheric pressure is the force per unit area exerted against a surface by the weight of

air above that surface in the Earth's atmosphere.

Wind is moving air and is caused by differences in air pressure within our atmosphere. Air

under high pressure moves toward areas of low pressure. The greater the difference in

pressure, the faster the air flows.

Rainfall: water falling in drops from vapor condensed in the atmosphere

Seasons

The Earth rotates about its axis, which is tilted at 23.5 degrees. This tilt and the sun's

radiation result in the Earth's seasons. The sun emits rays that hit the earth's surface at different

angles. These rays transmit the highest level of energy when they strike the earth at a right angle (90

°). Temperatures in these areas tend to be the hottest places on earth. Other locations, where the

sun's rays hit at lesser angles, tend to be cooler.

As the Earth rotates on its tilted axis around the sun, different parts of the Earth receive higher and

lower levels of radiant energy. This creates the seasons.

Student’s Manual For Level One and Two in Agriculture 14

Maldives is located at the equator and experiences monsoonal climate. Maldives has two distinct

seasons; dry season (northeast monsoon) and wet season (southwest monsoon). In these two

seasons the temperature varies hardly. Northeast monsoon extends from January to March. Since

Maldives consists of small islands and are surrounded by seas, hot days are often tempered by

cooling sea breezes and balmy evening temperatures.

Throughout the year, temperature remains almost same in the Maldives.However, daily

temperature ranges from around 31 degrees Celsius in daytime to 23 degrees Celsius in nighttime.

The maen daily maximum temperature for central parts ( Hulhule ) of the Maldives is 30.5 degree

Celsius and minimum temperature is 25.7 degree Celsius. On the other hand, mean daily maximum

and minimum temperature for South ( Gan ) is 30.9 and 24.5 degree Celsius, respectively.

Furthermore, mean daily maximum and minimum temperature for North ( Hanimaadhoo ) is 30.7

and 25.2 degree Celsius, respectively.

The highest temperature ever recorded in the Maldives was 36.8°C, recorded on 19 May 1991

at Kadhdhoo Meteorological Office. Likewise, the minimum temperature ever recorded in the

Maldives was 17.2°C, recorded at the National Meteorological Centre on 11th April 1978.

Student’s Manual For Level One and Two in Agriculture 15

The wet season- southwest monsoon runs from mid-May to November. In this season Maldives

experiences torrential rain. Central, Southern and Northern parts of the Maldives receive annual

average rainfall of 1924.7mm, 2277.8mm, and 1786.4mm, respectively. The highest rainfall ever

recorded in the Maldives with in 24 hour period was recorded on 9th July 2002 at Kaadedhdhoo

Meteorological Office and amounts to 219.8mm of rainfall. The fact that the Maldives is located at

the equator, Maldives receives plentiful of sunshine through out the year. On average Southern atolls

(Gan) of the Maldives receives 2704.07 hours of sunshine each year. Furthermore, on average

central (Hulhule) parts of the country receives 2784.51 hours of sunshine per year.

Evaporation is the process by which water is converted from its liquid form to its vapor form and

thus transferred from land and water masses to the atmosphere.

Wind speed: the higher the wind speed, the more evaporation

Temperature: the higher the temperature, the more evaporation

Student’s Manual For Level One and Two in Agriculture 16

Humidity: the lower the humidity, the more evaporation

Transpiration is the evaporation of water from the aerial parts of plants, especially leaves

but also stems, flowers and roots. Leaf surfaces are dotted with openings called stomata that are

bordered by guard cells. Collectively the structures are called stomata. Leaf transpiration occurs

through stomata, and can be as a necessary "cost" associated with many processes such as the

opening of the pistil and allowing the diffusion of carbon dioxide gas from the air for

photosynthesis. Transpiration also cools plants and enables mass flow of mineral nutrients and water

from roots to shoots.

PLANT SHOW EVAPROTRANSPIRATION

Student’s Manual For Level One and Two in Agriculture 17

Transpiration is the process where water contained in liquid form in plants is converted to

vapor and released to the atmosphere. Much of the water taken up by plants is released through

transpiration. It is difficult to separate the processes of evaporation and transpiration, so this

transfer of water is sometimes simply called evapotranspiration.

Transpiration rate of plants can be measured by a number of techniques, including potometers,

lysimeters, porometers, and heat balance sap flow gauges.

Desert plants and conifers have specially adapted structures, such as thick cuticles, reduced

leaf areas, sunken stomata and hairs to reduce transpiration and conserve water. Many cacti conduct

photosynthesis in succulent stems, rather than leaves, so the surface area of the shoot is very low.

Many desert plants have a special type of photosynthesis, termed Crassulacean acid metabolism or

CAM photosynthesis in which the stomata are closed during the day and open at night when

transpiration will be lower.

Stoma (also stomate; plural stomata) is a pore, found in the leaf and stem epidermis that is used

for gas exchange. The pore is bordered by a pair of specialized parenchyma cells known as guard

cells which are responsible for regulating the size of the opening.

Hydathode is a type of secretory tissue in leaves, usually of Angiosperms, that secretes water

through pores in the epidermis or margin of leaves, typically at the tip of a marginal tooth or

serration.

Student’s Manual For Level One and Two in Agriculture 18

Plants Experience Guttation

Guttation occurs only in vascular plants. That is, plants that have xylem, a specialized tissue,

to circulate water and nutrients throughout the plant. Almost all of the plants in your garden and

home are vascular plants. Vegetable plants, perennials, all flowering plants, trees, conifers, grasses

and ferns are vascular plants.

Guttation Take Place at Night

The conditions must be right for guttation to occur. Transpiration stops at night when the

stomata on leaves close. Water in the soil is absorbed by the roots of vascular plants by osmosis

when the water potential in the roots is lower than the water potential in the soil. Root pressure

forces the water up through the roots into the stems and leaves of plants.

Student’s Manual For Level One and Two in Agriculture 19

How Does the Liquid Get Out of the Leaf?

Specialized structures called hydathodes are located on the tips and edges of leaves. When

excess water accumulates in the leaf at night, the hydathodes open allowing water droplets to

escape. When these droplets evaporate in the morning, you might see a white residue or crust on

the leaves. This crust is caused when the sugars and minerals in the droplets of water are left behind

after evaporation.

How Do Plants Release Excess Water During the Day?

During the day, plants transpire, that is, release water vapor through the stomata. Stomata

are pores found on the epidermis (on the leaves and stems) of vascular plants. Stomata open in

response to light and close in the absence of light. Stomata also exchange oxygen for carbon dioxide.

Transpiration is the action of releasing water from the leaves and stems. Transpiration keeps plants

cool, draws water up from the roots into the leaves and stems and allows the movement of nutrients

and water through the xylem.

Why Doesn't Guttation Occur Every Night?

Guttation can only take place when there is more water in the soil than in the roots of the

plant. The water potential in the roots has to be lower than the water potential in the soil (the

amount of water in the roots is lower than the amount of water in the soil). This contributes to root

pressure. Root pressure supplies the means by which guttation takes place. Root pressure occurs at

night when stomata are closed and transpiration has stopped or during the day if transpiration is

slow. If water potential is balanced between roots and soil and there is no transpiration, there will be

no guttation.

Crops

Student’s Manual For Level One and Two in Agriculture 20

A crop is the annual or season's yield of any plant that is grown in significant quantities to be

harvested as food, as livestock fodder, fuel, or for any other economic purpose.

There are many types of crops that are used for industrial purposes. For example, crops are grown

and harvested for the sole purpose of making profit and feeding people, as they are grown in large

amounts in a certain area suitable for growing crops.

In agriculture, crop yield (also known as "agricultural output") is not only a measure of the yield of

cereal per unit area of land under cultivation, yield is also the seed generation of the plant itself (e.g.

one wheat grain produces a stalk yielding three grain, or 1:3] The figure, 1:3 is considered by

agronomists as the minimum required to sustain human life.

A measurement of the amount of a crop that was harvested per unit of land area. Crop yield is the

measurement often used for a cereal, grain or legume and is normally measured in metric tons per

hectare (or kilograms per hectare).

WEATHER AFFECTS CROPS YIELD

All external conditions and influences affecting the life and development of a crop.

Environmental Factors:

The following are regarded as the most important environmental factors

Temperature

Moisture supply

Radiant energy

Composition of the atmosphere

Soil aeration and soil structure

Soil reaction

Biotic factors

Supply of mineral nutrients

Absence of growth-restricting substances

Each can be a limiting factor in plant growth. These environmental factors do not act

independently example - inverse relationship between soil moisture and air

a) Temperature - A measure of the intensity of heat. Plant growth occurs in a fairly narrow

range between 60 - 100 degrees F

Student’s Manual For Level One and Two in Agriculture 21

1. Temperature directly affects

Photosynthesis

Respiration

Transpiration - loss of water

Absorption of water and nutrients

2. The rate of these processes increases with an increase in temperature responses are

different with different crops

3. Temperature also affects soil organisms nitrifying bacteria inhibited by low temperature.

pH may decrease in summer due to activities of microorganisms

4. Soil temperature affects water and nutrient uptake

b) Moisture supply - Plant growth restricted by low and high levels of soil moisture

1. Can be regulated with drainage and irrigation

2. Good soil moisture improves nutrient uptake

If moisture is a limiting factor fertilizer is not used efficiently.

c) Radiant energy - Quality, intensity and duration of light are important

1. Quality can't be controlled on a field scale - Feasible on specialty crops

2. Intensity of light (brightness) is an important factor.

photosynthesis light intensity

Corn with upright leaves being bred to intercept more light

3. Duration - Photoperiodism - Plant behavior in relation to day length

- long day plants - flower only if days are longer than same critical period - 12 hours Grains and

clovers

- short day plants - flower only if days are shorter than a critical period soybeans.

- indeterminate - flower over a wide range of day lengths. Tomato, cotton, buckwheat

Student’s Manual For Level One and Two in Agriculture 22

Some crops fail to flower in certain geographical areas

Chrysanthemums can be made to bloom by controlling photoperiod.

d) Composition of the atmosphere

CO2 makes up 0.03 per cent of air by volume. Photosynthesis converts CO2 to organic material in

the plant. CO2 is returned to atmosphere by respiration and decomposition

In a corn field or closed greenhouse CO2 level may drop and become a limiting factor in growth.

Increasing CO2 can increase crop yields respiration of plants and animals - decomposition of manure

or plant residue may release CO2

greenhouse crops

Plant growth and quality can be enhanced by supplemental CO2. Growth responses have been

shown with tomatoes, lettuce, cucumbers, flower crops, greens, peas, beans, potatoes

Air Quality

Air pollutants in sufficient quantities are toxic to plants sulfur dioxide - provides sulfur at low levels

carbon monoxide

hydrofluoric acid

e) Soil aeration

Compact soils of high bulk density and poor structure are aerated poorly.

Pore space is occupied by air and water so the amount of air and water are inversely proportional to

the amount of oxygen in the soil. On well drained soils, oxygen content is not likely to be limiting to

plant growth.

Plants vary widely in their sensitivity to soil oxygen. Paddy rice vs tobacco

f) Soil reaction

- pH influences availability of certain nutrients ex phosphate availability low on acid soils. Al is toxic

to plants

diseases affected by pH

Potato scab controlled by keeping pH below 5.5

Student’s Manual For Level One and Two in Agriculture 23

g) Biotic factors

disease - heavier fertilization may increase vegetative growth and susceptibility to disease

Root knot nematodes reduce absorption so more fertilizer is necessary.

insects

weeds - compete for moisture nutrients light

allelopathy - harmful substances released by roots.

h. Mineral nutrients essential nutrients - any element that functions in plant metabolism

Non-mineral nutrients (from water and air)

carbon, hydrogen, oxygen

Primary nutrients

nitrogen, phosphorus, potassium

Secondary nutrients

calcium, magnesium, sulfur

Micronutrients

copper, manganese, zinc, boron, molybdenum, chlorine, iron

Beneficial to some plants

cobalt, vanadium, sodium, silicon,

i. Absence of growth - restricting substances

High concentrations of plant nutrients

aluminum, nickel, lead - associated with sewage disposal, wastes from industry, mines, etc.

organic compounds - phenols, oil

Drought

A drought is an extended period of months or years when a region notes a deficiency in its water

supply.

Student’s Manual For Level One and Two in Agriculture 24

Flood A flood is an overflow of an expanse of water that submerges land. defines a flood as a temporary covering by water of land not normally covered by water. In the sense of "flowing water.

Thunder storms

Student’s Manual For Level One and Two in Agriculture 25

A storm (from Proto-Germanic *sturmaz "noise, tumult") is any disturbed state of an

astronomical body's atmosphere, especially affecting its surface, and strongly implying severe

weather. It may be marked by strong wind, thunder and lightning (a thunderstorm), heavy

precipitation,

Water Balance

Crop-yield formulation. Weather elements, e.g. precipitation, temperature & sunshine, influence the yield of

crops. In India,weather data are available over long periods for a large network of stations. Yield data for

different crops for periods ranging from 25-65 years are also available from different states. With the help of

these data, formulae have been evolved to forecast the yield of principal food crops(rice & wheat)

subdivision-wise by using regression techniques.

The linear correlation between rainfall & other recorded meteorological parameters & the yield of a

particular crop over a large number of years has been worked out for overlapping periods of 7-90

days on a very fast electronic computer. The significant periods, thus located, have been used for

final regression analysis.

These studies reveal that technology comprising improved methods of farming , the use of hybrid

seeds, fertilisers,etc. have enhanced the yields in almost all the sub-divisions of the country,

significantly in recent years. As regards weather, it had been noticed that whereas the distribution of

rainfall during the crop-growing season plays a very important role increasing the yield, the kharif

Student’s Manual For Level One and Two in Agriculture 26

rice temperature plays only a minor role. In respect of wheat, the pre-season precipitation during

September-October & the temperatures during the growing season are the main parameters which

control the yield. The in-season precipitation is of less importance.

Such forecasts are expected to help the Government to estimate the production of major crops well

before the harvest season. Formulae have been developed for a few major crops over a large part of

the country & test forecasts are being issued to the Directorate of Economics & Statistics of the

Ministry of Agriculture & Irrigation. Pilot studies to develop similar formulae for other major food

crops are also in progress.

Long-range forecasts of weather and crop yields. Indian agriculture mainly depends on the

monsoon rains. The farmers anxiously await the onset of the monsoon & a favourable distribution

of rainfall during the rainy season. As there is a considerable variation from year to year in the

advent of the monsoon over different divisions, the predicting of the dates of its onset & giving

advance indications to the probable distribution of rainfall are of great economic significance.

Agro-climatic zoning. Water deficit & water surplus are two parameters of great importance for

assessing the irrigation requirements & judging the agricultural potential of any place.

weather modification & crop production. Delays in the timely onset of rains & breaks in the rainy

spells during the cropping season are the two great problems which the Indian farmer has to

confront with, especially those in the dry farming tract. During the monsoon season, in some years,

over certain regions the rains abruptly cease. Although clouds persist in those areas, their vertical

extent is not large enough to precipitate. On such occasions, the clouds can be made to grow & shed

their moisture as rain through appropriate seeding.

The water droplet in a cloud grows a million times its original volume, each around a nucleus

present in the atmosphere to become a raindrop. In warm clouds (at temperature above freezing),

the growth occurs through coalescence of water droplets & in cold clouds (where the temperatures

are below freezing), the growth occurs through the formation of ice crystal. The technique of cloud-

seeding aims at correcting the deficiencies of nucleii in the cloud. Silver iodide is used for seeding

cold clouds whereas sodium chloride (common salt) is generally used for seeding warm clouds. The

seeding is effectively done with an aircraft flying inside the cloud.

Pests & diseases & the use of remote sensing through satellites. The damage caused by Pests &

diseases to crops is well known. The farmer has to contend with the ravaging effects of locust

swarms & diseases, e.g. the potato blight & the cereal rusts. Reduction in the losses caused by Pests

& diseases by timely & effective control measures will considerably add to food production in the

country. The incidence of Pests & diseases & their intensity are dependent on certain predisposing

weather conditions. A beginning has been made to compile information on the meteorological

conditions conducive to locusts infestation & migration. weather conditions predisposing the

Student’s Manual For Level One and Two in Agriculture 27

outbreak & spread of Pests & diseases affecting crop yields are being studied in collaboration with

the concerned organization.

Student’s Manual For Level One and Two in Agriculture 28

Module 3

Soils

Soils defined as the thin layer of earth’s crust which serves as a natural medium for the

growth of plants. Soils differ among themselves in some or all the properties, depending on the

differences in genetic and environmental factors. Soil provides nutrients, water, helps the roots to

obtain oxygen, and acts as an anchor to support plants. Thus, it is very important to study the

science of soil when studying agriculture.

Soil forming materials

Soils vary widely in composition and structure from place to place. Soils are formed through

weathering of minerals and organic matter. Weathering is the action of wind, rain, sunlight and

biological processes, which breaks parent material down into smaller particles and alters their

chemistry. Soils form from weathering in place although many soils are comprised entirely of

transported weathered material which could arrive with the waves. The proportions and types of

minerals and organic matter help determine the characteristics of a particular soil.

It is useful to know how the island soils have been formed. This will help us to better understand

how the soils were made, and why the soils on the ocean side are different from those on the lagoon

side. Island soils have basically been formed by the degradation of corals. Details of how island soils

are formed could be found in Chapter 2 of the Agriculture in the Atoll Environment by Wilco

Liebregts.

As they become older over the years, soils undergo changes. Leaves and dead plants provide food

for insects and other micro-organisms, which help decompose the tissues and thereby increase the

organic matter content of the soil, and which can be used by other plants, insects or micro-

organisms to grow. Once this material is decomposed it forms a dark layer on top of the soil which

is called humus.

Student’s Manual For Level One and Two in Agriculture 29

Soils can also deteriorate. When much of the vegetation is cleared the topsoil becomes exposed to

the sun. When it dries out, strong winds can blow the fertile layers away, leaving only the infertile

subsoil which consists of sand and rocks. It is not a good soil for growing plants. Man too can

change soils, making them worse by burning, removal of the fertile layer of topsoil, or clearing of

vegetation. When people burn trees or shrubs it will make charcoal, and can form a black layer in the

soil. The soil can also be made better, by adding organic materials such as compost.

Rocks are the chief sources for the parent materials over which soils are developed. There are three

main kinds of rocks

1. Igneous rocks,

2 .Sedimentary rocks and

3 .Metamorphic rocks

Soil Profile

It is a vertical section of the soil through all its

horizons and it extends up to the parent materials. In deep soil the soil profile may be studied up to

one meter and a quarter and in others up to the parent material.

In the Maldives a soil normally comprises of 2 horizons as follows:

A – Horizon (Top soil): consists of corals and layers of dark soil with a depth of 20-40cm.

B - Horizon (Sub soil): consist of reef limestone which is a hardpan. In some islands the hardpan

layer is about 30 cm thick and limits root development

Student’s Manual For Level One and Two in Agriculture 30

Soil Composition

Composition — Soil is composed from solid, liquid and gas phases. Water and soil air are

thus integral components of soils. Water occupies the void space between soil particles. Air occupies

the remaining void space, if any. Both water and air components of soils are important to plant

growth and other life in the soil profile of a particular ecosystem. Details of the main constituents

are given below. Soil includes different materials which provide the basic requirements for plant

growth.

The constituents of soil are:

(a) Minerals

(b) Water

(c) Air

(d) Organic matter

Soil Management

The quality of many soils in certain region can be improved with good management. Some

practices that are part of nutrient management plans may have unintended consequences that

degrade instead of improve soil quality. For example, it is often recommended that manure be

incorporated with tillage. However, tillage exposes the soil to erosion, reduces organic matter

content and can increase runoff. Facilities that store large amounts of manure may require heavy

manure spreading equipment, and often have a smaller time window for spreading, both of which

increase the risk of soil compaction. If nutrient management specialists can design plans that meet

soil conservation and soil quality considerations as well as nutrient management requirements, they

will do a great service to agricultural producers, other citizens, and the quality of natural resources in

the

feels soft and crumbles easily

drains well and warms up quickly in the spring

does not crust after planting

soaks up heavy rains with little runoff

stores moisture for drought periods

has few clods and no hardpan

resists erosion and nutrient loss

supports high populations of soil organisms

has a rich, earthy smell

does not require increasing inputs for high yields

produces healthy, high-quality crops

Student’s Manual For Level One and Two in Agriculture 31

Soil Testing

In agriculture a soil test is the analysis of a soil sample to determine nutrient content,

composition and other characteristics, including contaminants. Tests are usually performed to

measure fertility and indicate deficiencies that need to be remedied.

Soil characteristics can vary significantly from one spot to another, even in a small garden or field.

Taking samples everywhere in the field is crucial to get the most accurate measurement of nutrients

and other organisms. An example of this is along gravel roads where the soil could have more lime

from the dust from the roads settling down in the soil, or an old animal feedlot where phosphorus

and nitrogen counts could be higher than the rest of the field.

Sample depth is also an important factor. It is recommended that you take the samples from tillage

depth, as this is where the majority of the nutrients and elements are placed mechanically. The

presence of various nutrients and other soil components varies during the year, so sample timing

may also be important. A good time to take a sample for testing is in the fall after harvesting is

finished, but this isn't the only time it should be done.

Soils in Maldives

In the atoll soils found in the Maldives, most of the soil is made up of sand. There is a lot of

space in between the grains of the soil, which is mostly filled with air.

The soil does not hold water very well. The sand grains are loose; they do not stick together but fall

away from each other easily. We say that this soil has no structure. The soil on most of the islands in

the Maldives is not very good for plant growth. It has a thin layer of topsoil, contains few nutrients

for the plants, has little organic matter, and is only capable of holding water for a short period. We

say that the soils in the Maldives are generally poor. However there are also some advantages.

Generally there is no accumulation of water in the soil. Therefore the occurrence of soil-borne

diseases, or diseases arising from pathogens in the soil, is lower. There is enough air in the soil, and

the large pores make it easy for exchange of air from the atmosphere. The soils are also generally

good for enabling good root formation so that the plants can anchor themselves well and can resist

strong winds.

Characteristics of soils in the Maldives

The soil is derived from calcareous materials.

It is the weathered reef limestone, corals, mollusks and shells. Therefore it is called ―Coral Soil

The soil is relatively young and has no structure.

Student’s Manual For Level One and Two in Agriculture 32

A – Horizon (Top soil): consists of corals and layers of dark soil with a depth of 20-40cm.

B - Horizon (Sub soil): consist of reef limestone which is a hardpan. In some islands the hardpan

layer is about 30 cm thick and limits root development.

A very high pH (8 - 8.5) due to excessive calcium.

A very high infiltration rate.

A low water holding capacity.

Student’s Manual For Level One and Two in Agriculture 33

Module 4

Water

Humans depend on water in many ways, well beyond the few liters needed daily for

drinking. Water is also essential for the production of food. Various forms of agriculture, practiced

on about half of Earth's land surface, provide the vast majority of food that over 6 billion people

eat. Agriculture also provides much of the fiber for cotton, wool, and linen clothing

Water is one of the most valuable natural resources available to the farmer. It plays a vital role in

crop production. All plants require water for growth and development. A high percent of a growing

plant is comprised of water (70-90%). When water is not available some plants wilt and die

immediately, others remain alive but produce poorly or not at all.

Water has the following functions in relation to crop growth:

1. It keeps the plant turgid.

2. It carries nutrients/minerals within the plant.

3. It provides a cooling effect for the plant.

The amount of water taken up by the plants depends on:

1. The rate of transpiration

2. The amount of water present in the soil

3. The stage of growth of plant

Actively growing plants in full sun lose surprisingly large amounts of water from their leaves.

Water Resources

Water resources are sources of water that are useful or potentially useful to humans Uses of

water include agriculture and environmental activities. Virtually all of these human uses require fresh

water

Surface water Surface water is water in a river, lake or fresh water wetland Surface water is naturally

replenished by precipitation and naturally lost through discharge to the ocean, evaporation, and sub-

surface seepage.

Water shed, the timing of the precipitation and local evaporation rates. All of these factors also

affect the proportions of water lost.

Student’s Manual For Level One and Two in Agriculture 34

Human activities can have a large and sometimes devastating impact on these factors. Humans often

increase storage capacity by constructing reservoirs and decrease it by draining wetlands. Humans

often increase runoff quantities and velocities by paving areas and channelizing stream flow.

The total quantity of water available at any given time is an important consideration. Some human

water users have an intermittent need for water. For example, many farms require large quantities of

water in the spring, and no water at all in the winter. To supply such a farm with water, a surface

water system may require a large storage capacity to collect water throughout the year and release it

in a short period of time.

Ground water Sub-surface water, or ground water is fresh water located in the pore space of soil and

rocks It is also water that is flowing within aquifers below the water table .Sometimes it is useful to

make a distinction between sub-surface water that is closely associated with surface water and deep

sub-surface water in an aquifer (sometimes called "fossil water").

Sub-surface water can be thought of in the same terms as surface water: inputs, outputs and storage.

The critical difference is that due to its slow rate of turnover, sub-surface water storage is generally

much larger compared to inputs than it is for surface water. This difference makes it easy for

humans to use sub-surface water unsustainably for a long time without severe consequences.

Nevertheless, over the long term the average rate of seepage above a sub-surface water source is the

upper bound for average consumption of water from that source.

If the surface water source is also subject to substantial evaporation, a sub-surface water source may

become saline. This situation can occur naturally under closed basin bodies of water, or artificially

under irrigated farmland. In coastal areas, human use of a sub-surface water source may cause the

direction of seepage to ocean to reverse which can also cause soil salinisation. Humans can also

cause sub-surface water to be "lost" (i.e. become unusable) through pollution. Humans can increase

the input to a sub-surface water source by building reservoirs or detention ponds.

Desalination It is an artificial process by which saline water is converted to fresh water. The most

common desalination processes are distillation and reverse osmosis Desalination is currently

expensive compared to most alternative sources of water, and only a very small fraction of total

human use is satisfied by desalination. It is only economically practical for high-valued uses.

Student’s Manual For Level One and Two in Agriculture 35

Soil Water Storage

The soil is composed of three major parts: air, water, and solids .The solid component forms

the framework of the soil and consists of mineral and organic matter. The mineral fraction is made

up of sand, silt, and clay particles. The proportion of the soil occupied by water and air is referred to

as the pore volume. The pore volume is generally constant for a given soil layer but may be altered by

tillage and compaction. The ratio of air to water stored in the pores changes as water is added to or

lost from the soil. Water is added by rainfall or irrigation. Water is lost through surface runoff,

evaporation (direct loss from the soil to the atmosphere), transpiration (losses from plant tissue),

and either percolation (seepage into lower layers) or drainage.

Within the soil system, the storage of water is influenced by several different forces. The strongest

force is the molecular force of elements and compounds found on the surface of soil minerals. The

water retained by this force is called hygroscopic water and it consists of the water held within

0.0002 millimeters of the surface of soil particles.

The maximum limit of this water around a soil particle is known as the hygroscopic coefficient.

Hygroscopic water is essentially non-mobile and can only be removed from the soil through heating.

Matric force holds soil water from 0.0002 to 0.06 millimeters from the surface of soil particles. This

force is due to two processes: soil particle surface molecular attraction (adhesion and absorption) to

water and the cohesion that water molecules have to each other. This force declines in strength with

distance from the soil particle. The force becomes nonexistent past 0.06 millimeters. Capillary action

moves this water from areas where the matric force is low to areas where it is high. Because this

water is primarily moved by capillary action, scientists commonly refer to it as capillary water.

Plants can use most of this water by way of capillary action until the soil wilting point is reached.

Water in excess of capillary and hygroscopic water is called gravitational water. Gravitational water is

found beyond 0.06 millimeters from the surface of soil particles and it moves freely under the effect

of gravity. When gravitational water has drained away the amount of water that remains is called the

soil's field capacity

Student’s Manual For Level One and Two in Agriculture 36

The relationship between the thickness of water film around soil particles and the strength of the

force that holds this water. Force is measured in units called bars. One bar is equal to a 1000 mill

bars. The graph also displays the location of hygroscopic water, the hygroscopic coefficient, the

wilting point, capillary water, field capacity and gravitational water along this line.

Field capacity (F.C.) approximates the amount of water that is held in soil after it has been fully

wetted and all gravitational water has been drained away. In practice, field capacity is reached about

one to two days after heavy rainfall or irrigation ceases.

In practical terms, field capacity will be reached much faster in a coarser textured soil (e.g. Loamy

Sand) than in a fine-textured soil profile (e.g. Heavy Clay).

Field capacity is useful in practical terms because it is where a number of important processes are in

transition. At field capacity the soil holds the maximum amount of water that can be stored and can

be used by plants.

In addition, there is sufficient air-filled pore space to allow for the aeration of most aerobic

microbial activity and plant growth. Water in excess of field capacity drains to quickly for plant use

and reduces aeration. From a tillage point of view, soil turns to mud above field capacity and is

unworkable.

Field capacity corresponds to a soil water potential (Ψm) of about -10 to -33 J/kg m. In practice a

value of -33 J/kg is used. Because forces holding water are surface-attractive forces, the more

surface area a soil has the greater is the amount of water adsorbed.

Student’s Manual For Level One and Two in Agriculture 37

Relationship between soil water film thickness and moisture tension.

Irrigation

Irrigation is the replacement or supplementation of rainfall with water from another source

in order to grow crops or plants.

In the Maldives, ground water is the most common source of water for plants between rains. Thus

the water source for irrigation is normally the wells in the field. However the water collected through

the harvesting of rain that falls on the roofs of buildings is also used, especially in hydroponics.

Various types of irrigation techniques differ in how the water obtained from the source is distributed

within the field. In general, the goal is to supply all the plants in the field uniformly with water, so

that each plant has the amount of water it needs, neither too much nor too little. It is also important

to provide it at the time needed.

Generally in the Maldives, irrigation is done daily due to the poor water holding capacity of the soil.

However, in very hot and dry weather conditions, sometimes irrigation has to be done even twice a

day.

Types of Irrigation

Surface Irrigation

Hand watering

Surface irrigation generally means watering plants by

flooding and furrowing. However, in the Maldives this is not

a practical way of watering. In the Maldives, water used to

be applied to the bottom of the plants manually using

watering cans This is a difficult task; therefore farmers now

also use pumps to extract water from shallow dug wells.

Water runs through a hose pipe and the farmer applies the

water to the soil surrounding an individual plant, or use

improvised sprinkler systems.

Different simple practices are used to facilitate hand watering as this is a daily task, and as water is

heavy to carry. Pipes are laid on the field with taps at different locations and different types of

containers are used to collect water at these locations. Measures are also taken to reduce difficulties

in filling and carrying water

Student’s Manual For Level One and Two in Agriculture 38

Pipes at different locations in the field Container to facilitate quick filling of watering can Surface irrigation generally means watering plants by flooding and furrowing. However, in the

Maldives this is not a practical way of watering. In the Maldives, water used to be applied to the

bottom of the plants manually using watering cans. This is a difficult task; therefore farmers now

also use pumps to extract water from shallow dug wells. Water runs through a hose pipe and the

farmer applies the water to the soil surrounding an individual plant, or use improvised sprinkler

systems.

Different simple practices are used to facilitate hand watering as this is a daily task, and as water is

heavy to carry. Pipes are laid on the field with taps at different locations and different types of

containers are used to collect water at these locations. Measures are also taken to reduce difficulties

in filling and carrying water.

Stand to minimize water spilling out of the can In the future if large numbers of farmers extract large volumes of water it can be detrimental to the

water table. This is because salt water can flow into the wells. Therefore, in the future it is important

Student’s Manual For Level One and Two in Agriculture 39

to ensure that a proper plan with respect to the maximum amount of water that could be harvested,

especially during a drought, is followed.

Overhead irrigation

In overhead, or sprinkler irrigation, water is piped to locations within the field and

distributed by overhead pressure sprays.

A system utilizing sprinklers mounted overhead on permanently installed risers is often referred to

as a solid-set irrigation system. Manually assembled systems of piping that are broken down to

permit tillage and harvesting are sometimes called "hand set" or "hand move pipe".

Some sprinklers can also be hidden below ground level, if aesthetics is a concern. They are designed

to pop up in response to increased water pressure. This type of system is commonly used in lawns,

and parks and other turf areas. For resorts too this could probably be preferable. Sprinklers that

spray in a fixed pattern are generally called sprays or spray heads.

One drawback of overhead irrigation is that much water can be lost because of high winds or

evaporation, and irrigating the entire field uniformly can be difficult if the system is not properly

designed. Water remaining on plants' leaves may promote fungal and other diseases. If fertilizers are

included in the irrigation water, plant leaves can be burned, especially on hot, sunny days.

Overhead irrigation is generally the best solution for watering lawns.

Maldivian farmers have shown a lot of innovativeness and ingenuity in fabricating low cost irrigation

systems with available material.

Innovative Sprinkler PET bottle used for sprinkler

Student’s Manual For Level One and Two in Agriculture 40

Mobile sprinkler Flattened PVC pipe with flexible hose

Lawn sprinkler Flattened PVC pipe with flexible hose

Drip Irrigation

Drip irrigation is sometimes also referred to as trickle irrigation. Water is delivered at or near

the root zone of plants, drop by drop. This type of system can be the most water-efficient method

of irrigation, if managed properly, since evaporation and runoff are minimized. In modern

agriculture, drip irrigation is often combined with a plastic mulch, further reducing evaporation, and

is also the means of delivery of fertilizer. The process is known as fertigation.

Deep percolation, where water moves below the root zone, can occur if a drip system is operated

for too long of a duration. Lower water pressures are usually needed. The system can be designed

for uniformity throughout a field or for precise water delivery to individual plants in a landscape

containing a mix of plant species. Both pressure regulation and filtration to remove particles are

important. The tubes are usually black (or buried under soil or mulch) to prevent the growth of algae

and to protect the polyethylene from degradation due to ultraviolet light. But drip irrigation can also

be as low-tech as a porous clay vessel sunk into the soil and occasionally filled from a hose or

bucket.

Student’s Manual For Level One and Two in Agriculture 41

Irrigation Requirements

Due to the soil conditions in the Maldives where the soil cannot hold a lot of water, farmers

generally water the plants each day unless it rains. Generally irrigation is done at around 9.00 a.m.

However, in very hot and dry periods sometimes irrigation has to be done even twice a day, and is

normally done before Asru prayers in the afternoon.

For an area about 400 sq. metros about 1000 liters of water per day is required. Young plants use

less water.

The amount of water taken by the plants depends on:

(a) The rate of transpiration.

(b) The amount of water present in the soil.

(c) The stage of growth of plant.

Actively growing plants in full sun lose surprisingly large amounts of water from their leaves.

Irrigation is determined by the following factors:

(a) The amount of rainfall

(b) The rate of transpiration and evaporation

(c) The type of soil

(d) The crop grown

(e) Cost of irrigation

(f) The water table or the water available in the ground

When irrigating one must apply water rationally. Water should not be wasted, as it is a scarce

resource. As a rule of thumb, water until a soil depth of 10 – 20 cm inches is thoroughly wet. Water

the soil around the plant, not just the plant.

If irrigation is not properly applied it can have adverse outcomes such as:

(a) Leaching, which is the loss of nutrients to lower layers, and thus become unavailable to the plant

(b) Destruction of soil structure

(c) Erosion of top soil

A simple irrigation system

The beginning of an irrigation system is the water source. This is usually the well. A pump is also needed. Apart from that the

pipes to carry the water, and joints etc. are also needed. An irrigation system

Student’s Manual For Level One and Two in Agriculture 42

The well

Due to the relatively high water table very often only a shallow well is dug. Some being extremely

shallow If the soil has a hardpan close to the surface, and the walls of the well are hard a

supporting wall may not be needed. However, if the soil is loose, and especially if the well will be

used for more than one season, a structure is important to prevent the soil falling in to the well. A

number of different ways are used to provide this support to the wall of the well. It may be a iron

barrel or a cement structure.

Well through hard pan Iron barrel as well

Cement block well Cement block well

Student’s Manual For Level One and Two in Agriculture 43

Covered well The engine of the pump could be either a petrol

Petrol pump Electric pump

An irrigation system also requires pipes and

components such as T joints, elbows, reducing sockets,

ball valves, flexible hose etc.

Student’s Manual For Level One and Two in Agriculture 44

Components of the pipes

Given below is an example of an irrigation system for a 30 m x 30 m (100‘ x 100‘) plot of a

plant such as cucumber. It should be noted that the specific design could differ according to the

plant type, depth of well, distance of carrying water, pressure needed etc.

A layout for an efficient irrigation system is given in the picture It indicates the spatial arrangement

as well as the distance between the different components of the system. Details of the pipe fittings,

and how they are joined is seen in the picture.

Layout of simple irrigation system

Student’s Manual For Level One and Two in Agriculture 45

Details of components of irrigation system

In general, the well should be around 1.5 m (5‘) deep, and have a diameter of 1.8 m (6‘). However,

due to the nature of the soil, the recharge rate of water to the wells is high, and hence in many

farms, the size of the well is smaller. This is specially the case if the plot size is not too big.

One pump is generally sufficient to meet the requirements of 5 fields of the size 30 m x 30 m (100‘ x

100‘).

It is preferable to bury the main 2‖ pipe. This reduces the effect of UV light on the pipe and thus

increases its life, as UV light has a damaging effect on plastics. It will also help in not increasing the

temperature of the water supplied to the plant. If it is not buried, the pipe could get heated in the

hot sun, especially if it is black, and thus the water supplied through it to the plant could get heated.

The material needed for the above system is given below in table.

# Item Qty

1 Pump-2” Petrol 1

2 2”PVC Pipes 8

3 2”Faucet Socket 2

4 2”Foot Valve 1

5 PVC Glue 1

6 2” Elbow 3

7 2” Joint 4

8 2” to 1/2” Reducing T 4

9 ½” Elbow 4

10 ¾” Reel soft pipe 2

11 ½” PVC Pipe 1

12 2” Cap 1

13 ½” Ball 4

Student’s Manual For Level One and Two in Agriculture 46

Module 5

Land Utilization

Land Uses

Different land uses and the degree of intensity of various land uses lead to a tension in

Landscape development, especially when requirements of nature protection and economic Interests

are contradictory. This paper provides spatial analysis and solution of different

Interventions, that means mental attitudes and resistances as well as real ones. Land use

Intensity of agricultural areas is roughly estimated by the land use categorization of the

Land Cover programme.

These two land use aspects are compared to a scientifically deduced environmental

indicator, called “need of protection of the landscape for maintenance of biodiversity”. The

main driving forces and their influences can be identified by looking at the different criteria

leading to the environmental indicator value. Changes of land use intensity including nature

protection obligations will lead to changes of the “need of protection of the landscape”

Whereby different ways of development – nearby all combinations of aspects - could be the

case. Following spatial aspects are discussed

level of need of protection of landscape for maintenance of biodiversity, Agricultural activity, Existing nature protection requirements and “Hot spots” of growth of Building Area.

Classification of land uses:

1. Forests

2. Area not available for cultivation

3. Other uncultivated land

4. Fallow land

5. Net area sown

Different types of Lands Depending upon the purpose or necessity, different types of tillage are carried out. They are

deep ploughing, sub soiling and year-round tillage.

Deep ploughing turns out large sized clods, which are baked by the hot sun when it is done in

summer. These clods crumble due to alternate heating and cooling and due to occasional summer

showers. This process of gradual disintegration of clods improves soil structure. The rhizomes and

tubers of perennial weeds die due to exposure to hot sun. Summer deep ploughing kills pests due to

exposure of pupae to hot sun.

Student’s Manual For Level One and Two in Agriculture 47

Deep tillage also improves soil moisture content. However the advantage of deep tillage in dry

farming condition depends on rainfall pattern and crop.

It is advisable to go for deep ploughing only for long

duration, deep rooted crops. Depth of ploughing should

be related to the amount of rainfall that it can wet.

Tillage operations carried out throughout the year are known as year-round tillage. In dry farming

regions, field preparation is initiated with the help of summer showers. Repeated tillage operations

are carried out until sowing of the crop. Even after harvest of the crop, the field is repeatedly

ploughed or harrowed to avoid weed growth in the off season

Lighter or finer operations performed on the soil after primary tillage are known as secondary tillage.

After ploughing, the fields are left with large clods with some weeds and stubbles partially uprooted.

Harrowing is done to a shallow depth to crush the clods and to uproot the remaining weeds and

stubbles. Disc harrows, cultivators, blade harrows etc., are used for this purpose.

After the seed bed preparation, the field is laid out properly for irrigation and sowing or planting

seedlings. These operations are crop specific. For most of the crops like wheat, soybean, pearl millet,

groundnut, castor etc., fIat leveled seedbed is prepared. After the secondary tillage, these crops are

sown without any land treatments. However, growing crops during rainy season in deep black soils

is a problem due to ill-drained conditions and as tillage is not possible during the rainy season.

For some crops like maize, vegetables etc., the field has to be laid out into ridges and furrows.

Sugarcane is planted in the furrows or trenches. Crops like tobacco, tomato, chillies are planted with

equal inter and intra-row spacing so as to facilitate two-way intercultivation. After field preparation,

a marker is run in both the directions. The seedlings are transplanted at the intercepts.

After the seedbed preparation, the field is laid out properly for irrigation and sowing or planting

seedlings. These operations are crop specific. For most of the crops like wheat, soybean, pearl millet,

groundnut, castor etc., fIat leveled seedbed is prepared. After the secondary tillage, these crops are

sown without any land treatments. However, growing crops during rainy season in deep black soils

Student’s Manual For Level One and Two in Agriculture 48

is a problem due to ill-drained conditions and as tillage is not possible during the rainy season. Broad

bed and furrows (BBF) are, therefore, formed before the onset of monsoon and dry sowing is

resorted to.

Forest

Forests provide multipurpose benefits such as timber, fodder, fuel and minor forest

produces. They also help in conserving soil and water, offering food and shelter for wild life, adding

to the aesthetic value and recreational needs of man. Forestry has the prime objective of developing

and protecting forests for their maximum productivity

Forests can be found in all regions capable of sustaining tree growth, at altitudes up to the tree line

except where natural fire frequency or other disturbance is too high, or where the environment has

been altered by human activity. Forest can be divided in to different types, they are

Boreal forest occupy the subarctic zone and are generally evergreen and coniferous.

Temperate zones support both broadleaf deciduous forests (e.g., temperate deciduous forest)

and evergreen coniferous forests (e.g., Temperate coniferous forests and Temperate

rainforests). Warm temperate zones support broadleaf evergreen forests, including laurel

forest

Tropical and Subtropical forests include Tropical and subtropical moist forest, Tropical and

sub tropical dry forest and Tropical and sub tropical coniferous forests.

Physiognomy classifies forests based on their overall physical structure or developmental

stage (e.g. old growth vs. second growth).

Forests can also be classified more specifically based on the climate and the dominant tree

species present, resulting in numerous different Forest types(e.g., ponderosa pine/Douglas-

fir forest).

Student’s Manual For Level One and Two in Agriculture 49

Irrigated area

Water is an important determinant factor of production of crops in agriculture sector.

Intensive and extensive cultivation of land depend mainly on the availability of water. Medium and

minor irrigation schemes are implemented in the state for augmenting the irrigation for agriculture.

Drip irrigation refers to application of water in small quantity as drops to the zone of the plants

through a network of plastic pipes fitted with emitters. Drip irrigation in its present form has

become compatible with plastics that are durable and easily moulded into a variety and complexity

of shapes required for pipe and emitters.

MERITS

1. Increased water use efficiency

2. Better crop yield

3. Uniform and better quality of the produce

4. Efficient and economic use or fertilizer through fertigation

5. Less weed growth

6. Minimum damage to the soil structure

7. Avoidance of leaf burn due to saline soil

8. Usage in undulating areas and slow permeable soil

9. Low energy requirement (i.e.) labour saving

Soil Organisms

Microorganisms are tiny units of life that are too small to be seen with the naked eye and

they exist everywhere in nature. Microorganisms are crucial for maintaining the ecological balance.

They carry out chemical processes that make it possible for all other organisms including humans to

live. There are friendly guys of the microbial worlds known as beneficial microorganisms and a not

so friendly group called pathogens that are harmful and capable of producing disease, decay and

pollution.

Student’s Manual For Level One and Two in Agriculture 50

Soil is the natural habitat for many organisms. Large organisms, such as earthworms, which

can be seen by the naked eye, and also very tiny micro-organisms that can be viewed only with a

microscope. . Earthworms living in the soil are known to be the most beneficial to the soils. The

tunnels made by the movements of the earthworm allow circulation of air and water, thus making

them more fertile. The excreta of the worms add organic matter to the soil, which contains many

nutrients for the plants. Together with the microscopic organisms they help turn the decaying plant

and animal matter into a dark material called humus‘, which is very rich in plant nutrients. They then

help to mix the humus with the upper layers of the top soil, so that it becomes more easily available

to the plants. Micro-organisms such as protozoa, saprophytic fungi and beneficial bacteria are

numerous in the soil and also help soil enrichment.

Student’s Manual For Level One and Two in Agriculture 51

Module 6

Soil and Water conservation

Types of Soil

Soil is the thin layer on the surface of the Earth on which the living beings of the earth survive since it is the

layer of materials in which plants have their roots. Soil is made up of many things like weathered rock

particles and decayed plant and animal matter. It takes a long time for soil formation and more than thousand

years for the formation of a thin layer of soil. Since soil is made up of such diverse materials like broken

down rock particles and organic material, it can be classified into various types, though based on the size of

the particles itcontains.

Soil Types

Therefore depending on the size of the particles in the soil, it can be classified into these following types:

Sandy soil

Silty soil

Clay soil

Loamy Soil

Peaty Soil

Chalky Soil Sandy soil

This type has the biggest particles and the size of the particles does determine the

degree of aeration and drainage that the soil allows. It is granular and consists of

rock and mineral particles that are very small. Therefore the texture is gritty and

sandy soil is formed by the disintegration and weathering of rocks such as limestone,

granite, quartz and shale. Sandy soil is easier to cultivate if it is rich in organic material but then it allows

drainage more than is needed, thus resulting in over-drainage and dehydration of the plants in summer. It

warms very fast in the spring season. So if you want to grow your plant in sandy soil it is imperative that you

water it regularly in the summers and give a break in the winters and rainy season, sandy soil retains moisture

and nutrients. In a way sandy soil is good for plants since it lets the water go off so that it does not remain

near the roots and lead them to decay.

Silty soil

It is considered to be one of the most fertile of soils. It can occur in nature as soil

or as suspended sediment in water column of a water body on the surface of the

earth. It is composed of minerals like Quartz and fine organic particles. It is

granular like sandy soil but it has more nutrients than sandy soil and it also offers

better drainage. In case silty soil is dry it has a smoother texture and looks like

dark sand. This type of soil can hold more moisture and at times becomes compact. It offers better drainage

and is much easier to work with when it has moisture.

Student’s Manual For Level One and Two in Agriculture 52

Clay soil

Clay is a kind of material that occurs naturally and consists of very fine grained

material with very less air spaces, that is the reason it is difficult to work with

since the drainage in this soil is low, most of the time there is a chance of water

logging and harm to the roots of the plant. Clay soil becomes very heavy when

wet and if cultivation has to be done, organic fertilizers have to be added. Clay soil is formed after years of

rock disintegration and weathering. It is also formed as sedimentary deposits after the rock is weathered,

eroded and transported.

Loamy Soil

This soil consists of sand, silt and clay to some extent. It is considered to be the

perfect soil. The texture is gritty and retains water very easily, yet the drainage is well.

There are various kinds of loamy soil ranging from fertile to very muddy and thick

sod. Yet out of all the different kinds of soil loamy soil is the ideal for cultivation.

Peaty Soil

This kind of soil is basically formed by the accumulation of dead and decayed

organic matter; it naturally contains much more organic matter than most of the

soils. It is generally found in marshy areas. Now the decomposition of the organic

matter in Peaty soil is blocked by the acidity of the soil. This kind of soil is formed

in wet climate. Though the soil is rich in organic matter, nutrients present are fewer

in this soil type than any other type. Peaty soil is prone to water logging but if the soil is fertilized well and the

drainage of the soil is looked after, it can be the ideal for growing plants.

Chalky soil Unlike Peaty soil, Chalky soil is very alkaline in nature and consists of a large number

of stones. The fertility of this kind of soil depends on the depth of the soil that is on

the bed of chalk. This kind of soil is prone to dryness and in summers it is a poor

choice for plantation, as the plants would need much more watering and fertilizing

than on any other type of soil. Chalky Soil, apart from being dry also blocks the

nutritional elements for the plants like Iron and Magnesium.

Besides this kind of classification soil can also be classified as Acidic and Alkaline soil depending on the

amount of humus, organic matter and the underlying bedrock. Every soil has its own advantages and

disadvantages and there are various plants that have different requirements. All plants do not need the same

kind of soil.

Erosion

Soil erosion losses are caused by wind, water, and movement in response to gravity. Erosion is a natural

process, but in many places it is increased by human land use. Poor land use practices include deforestation,

Student’s Manual For Level One and Two in Agriculture 53

overgrazing, and improper construction activity. Although overgrazing may not be a problem at present, if

animal husbandry such as goat production is to be introduced, this potential problem should be borne in

mind. Improved management can limit erosion using techniques like limiting disturbance during construction,

avoiding construction during erosion prone periods, intercepting runoff, terrace-building, use of erosion

suppressing cover materials, and planting tress or other soil binding plants. One of the main causes of soil

erosion is slash and burn treatment of forested areas. When the total ground surface is laid bare of vegetation,

the upper soils are vulnerable to both wind and water erosion.

Water Erosion

Soil erosion caused by water can be distinguished in three forms,

! Sheet erosion Is the detachment of soil particles by raindrop impact and their removal down slope by water flowing

overland as a sheet instead of in definite channels or rills. The impact of the raindrop breaks apart the soil

aggregate. Particles of clay, silt and sand fill the soil pores and reduce infiltration. After the surface pores are

filled with sand, silt or clay, overland surface flow of water begins due to the lowering of infiltration rates.

Once the rate of falling rain is faster than infiltration, runoff takes place. There are two stages of sheet

erosion. The first is rain splash, in which soil particles are knocked into the air by raindrop impact. In the

second stage, the loose particles are moved down slope by broad sheets of rapidly flowing water filled with

sediment known as sheet floods. This stage of sheet erosion is generally produced by cloudbursts, sheet

floods commonly travel short distances and last only for a short time.

!Rill Erosion

When Sheet erosion is allowed to continue unchecked, the silt laden run-off forms a well defined, but minute

finger shaped grooves over the entire field. Such thin channeling is known as rill erosion

!Gully erosion

It is also called ephemeral gully erosion, occurs when water flows in narrow channels during or immediately after

heavy rains or melting snow. This is particularly noticeable in the formation of hollow ways, where, prior to

being tarmacked, an old rural road has over many years become significantly lower than the surrounding

fields.

Wind erosion

Our natural environment comprises a number of elements that are affected in

quantum by the presence of external forces like wind, water and ice. Soil, rock

and sediments from river beds and mountainous terrain are displaced by these

forces regularly, by the minute. While the force of gravity is the major influencing

factor, burrowing animals and chemical or physical weathering are also responsible for erosion. Erosion

occurs concurrently, with the slightest shift in velocity or movement of the force responsible. Wind erosion is

Student’s Manual For Level One and Two in Agriculture 54

a natural process, but can also be induced or magnified via indiscriminate land use, deforestation

unmonitored construction, overgrazing and urbanization

Factors influencing Erosion and its control measures

1. Artificial Wind Barrier

Artificial Wind Barrier means a physical barrier to the wind. Artificial wind barriers disrupt the erosive flow of

wind over unprotected areas thus helping to reduce crop damage.

Suggestions for Implementation

Continuous board fences, burlap fences, crate walls, bales of hay and similar material can be used to

control air currents and blowing soil.

Barriers should be aligned across the prevailing wind direction. While 90 degrees or perpendicular is

preferred, benefits can still be realized when barriers are aligned as close to perpendicular as possible.

The distance of 10 times the barrier height is considered the protected area downwind of the barrier.

2. Cover Crop

Cover Crop means plants or a green manure crop grown for seasonal soil protection or soil improvement.

Cover crops help control soil movement and protect the soil surface between crops. Cover crop reduces wind

erosion by shielding the soil with vegetation and anchoring the soil with roots.

Suggestions for Implementation

Cover crops consist of any vegetative cover that maintains more than 60 percent ground cover.

Short-term cover is grown between major crops. Plants are then tilled into the soil prior to or during major

crop planting. Longer-term cover may be maintained by periodic mowing to maintain at least 60 percent

cover.

3. Cross-Wind Ridges

Cross-Wind Ridges means soil ridges formed by a tillage operation. Ridges formed by tillage operations create

protective windbreaks that disrupt the erosive forces of high winds.

Suggestions for Implementation

Ridges formed by tillage or planting should be aligned across the prevailing wind direction.

While 90 degrees or perpendicular is preferred, benefits can still be realized with ridges as close to

perpendicular as possible. If ridges deteriorate and become ineffective due to weathering or erosion, they

should be reestablished, unless doing so would damage a growing crop. This practice is Good adapted on

soils, which are stable enough to sustain effective ridges, such as clayey, silty and sandy loam soils. It is not

well adapted on unstable soils, such as sands, loamy sands and certain organic soils.

Student’s Manual For Level One and Two in Agriculture 55

4. Cross-Wind Strip-Cropping

Cross-Wind Strip-Cropping means planting strips of alternating crops within the same field.

Growing crops or managing residue as a protective cover in strips across the prevailing wind direction can

break the effects of high wind events.

Suggestions for Implementation

Cross-wind strip-cropping system consists of at least two crop or residue cover alternating strips.

Strip widths should be at least 25 feet but no more than 330 feet. Strips should be aligned across the

prevailing wind direction. While 90 degrees or perpendicular is preferred, benefits can still be realized when

the strips are oriented as close to perpendicular as possible. Protective cover includes, but is not limited to a

growing crop, grasses, legumes, grass-legume mixtures, standing stubble or tilled residue with enough surface

cover to provide protection.

5. Cross -Wind Vegetative Strips

Cross-Wind Vegetative Strips means herbaceous cover established in 1 or more strips within the same field.

Herbaceous cover creates a protective windbreak that disrupts the erosive forces of high winds, especially

during critical wind erosion periods.

Suggestions for Implementation

Herbaceous cover should be composed of perennial or annual vegetation, growing or dead.

Strips consist of at least one row of plants, providing the porosity can be achieved with a single row that

contains no gaps. When two or more rows are required to achieve the required porosity and to avoid gaps,

the rows should be spaced no more than 36 inches apart. Annual vegetation strips be composed of more than

one row. Strips designed for this purpose have a minimum expected height of two feet. Strips designed for

this purpose achieve a minimum porosity of 40 to 50 percent. Spacing between strips (not within row) not

exceeds 12 times the expected height of the herbaceous cover. Spacing between strips is adjusted to

accommodate widths of farm equipment to minimize partial or incomplete passes.

6. Manure Application

Manure Application means applying animal waste or bio-solids to a soil surface. Applying manure to maintain

or improve chemical and biological condition of the soil can help reduce wind erosion.

Student’s Manual For Level One and Two in Agriculture 56

Suggestions for Implementation

• If the application or storage of manure is near a water source, precautions should be taken to prevent accidental leakage, spillage or runoff that will result in undesirable effects on soil, water and plants.

• Caution should be used when applying manure to ensure that state and local regulations are not violated.

• Caution should be used when certain manures are applied as they can volatilize and contribute to odor and

ammonia emissions.

• Manures should be incorporated as quickly as possible to reduce odor and ammonia emissions, and to

preserve nutrient value if the area is to be cropped in the future.

7. Mulching

Mulching means applying plant residue or other material that is not produced on site to a soil surface Adding

a protective layer to the soil surface reduces soil movement in high wind events.This practice also conserves

soil moisture, which can reduce surface movement of soil.

Suggestions for Implementation

• This practice can be used after low residue producing crops, like cotton, are harvested.

• Materials for mulching are acquired as waste products from other enterprises.

• These include, but are not limited to, wood bark, chips, shavings, and saw dust; food processing wastes; and

small grain straw/chaff.

• Mulches are applied by blowers, hydro applicators, disk type straw punchers and spreaders.

• When small grain straw is used, spread at least 4,000 pounds straw per acre, distribute evenly and partially

incorporate into the soil.

• When wood fibers are used, spread at least 2,000 pounds per acre or achieve 80 percent cover.

8. Permanent Cover

Permanent Cover means a perennial vegetative cover on cropland. Maintaining a long-term (perennial)

vegetative cover on cropland that is temporarily not producing a major crop protects the soil surface from

erosive winds.

Student’s Manual For Level One and Two in Agriculture 57

Suggestions for Implementation

Perennial species of grasses and/or legumes be used to establish at least 60 percent cover.

When perennial species are used, maintenance by periodic mowing or swathing/baling is encouraged.

9. Residue Management

Residue Management means managing the amount and distribution of crop and other plant residues on a soil

surface. Leaving crop and other plant residues on the soil surface can protect the soil between the time of

harvest of one crop and emergence of a new crop, thus helping reduce wind erosion.

Suggestions for Implementation Many different residue management systems have been developed. Some examples include:

Reduced tillage systems, such as mulch-till, which partially incorporate surface residues and involve

no plowing.

No-till, this involves planting directly into the soil without any alteration to the seedbed. One

example is planting a new crop directly into the grain stubble.

Soil protection by crop residues can be increased by leaving residues on the soil surface as long as

possible (e.g. by delaying tillage operations until just before planting).

It is recommended that:

Stubble should be left standing at six inches or more.

Tillage must be limited during this period to undercutting tools, such as blades, sweeps or deep tillage

implements, such as a ripper or subsoiler.

Loose residue must be uniformly distributed on the soil surface.

Residues from previous crops must be left to maintain 60 percent ground cover.

10. Sequential Cropping

Sequential Cropping means growing crops in a sequence that minimizes the amount of time bare soil is

exposed on a field. By reducing the amount of time bare soil is exposed; sequential cropping helps reduce the

window of time that the cropland is susceptible to erosion. Planting a winter grain crop between final

harvests of a cotton crop and planting of the next cotton crop. Close rotations of vegetable crops.

Student’s Manual For Level One and Two in Agriculture 58

Suggestions for Implementation The amount of time bare soil is exposed be limited to 30 days or less. Rotations may be provided for

acceptable substitute crops in case of crop failure or shift in planting intentions for weather related or

economic reasons.

11. Surface Roughening

Surface Roughening means manipulating a soil surface to produce or maintain clods.The formation of clods

helps disrupt the erosive force of the wind over an unprotected soil surface. Soil clods can be formed by

tillage implements under appropriate soil moisture conditions.

Suggestions for Implementation

Not all soils are able to form clods. Review the local soil survey or contact the Soil testing office to

help determine a specific field’s soil type.

Caution should be used to determine the most opportune time to roughen the soil surface while

considering the tillage needed prior to planting, crop to be grown and irrigation water management

needs (surface roughening can dry the upper soil profile more rapidly than not disturbing the soil).

12. Transgenic Crops

Transgenic Crops means the use of plants that are genetically modified. Transgenic crops reduce the need for tillage or cultivation operations, as well as reduces soil disturbance.

13. Tree, Shrub, or Windbreak Planting

Tree, Shrub, or Windbreak planting means providing a woody vegetative barrier to the wind. Barriers placed

perpendicular to the wind direction can reduce wind speeds by changing the pattern of airflow over the land

surface, which helps to reduce wind erosion.

Suggestions for Implementation

The distance of 10 times the barrier height is considered the protected area downwind of the barrier.

Single row plantings are most popular in field windbreaks because they use less water and occupy the

least amount of land area for the amount of protection derived.

Recommended species for planting can be obtained at all NRCD offices.

Student’s Manual For Level One and Two in Agriculture 59

The planting should be done at a time and manner to insure survival and growth of selected species.

Moisture conservation or supplemental watering should be provided for plant establishment and

growth, as well as the use of drought tolerant species.

Windbreaks should be aligned across the prevailing wind direction. While 90 degrees or

perpendicular is preferred, benefits can still be realized when windbreaks are aligned as close to

perpendicular as possible.

The interval between windbreaks should be determined using current approved wind erosion

technology.

Contour farming

It helps to control run off velocity. The embankment may be closed or open, surplus arrangements are

provided wherever necessary.

COST

Approximate cost of laying contour bund is Rs.1400 / ha.

i. It can be adopted on all soils

ii. It can be laid up to 6% slopes.

iii. It helps to retain moisture in the field

Student’s Manual For Level One and Two in Agriculture 60

Mulching

A mulch is a protective cover placed over the soil, primarily to modify the effects of the micro

climate which is the climate around the plant. A wide variety of natural and synthetic materials are

used. A mulch is used for various purposes as given below:

To control weeds by blocking the sunlight necessary for germination.

To retain water by slowing evaporation.

To add organic matter and nutrients to the soil through the gradual breakdown of the mulch

material.

For erosion control - protects soil from rain and preserves moisture.

For sediment control - slows runoff velocity.

To adjust soil temperature. By keeping soil cool and evening out temperature swings during hot and

variable conditions.

A variety of materials can be used as mulch:

Organic residues – Weeded plants, coconut husks, leaves , coconut leaves in front, other leaves

behind, bag with leaves), newspaper, cardboard , grass clippings (in resorts), sawdust, etc.

Compost - This relies on fully composted material, where potential weed seed has been eliminated,

or else the mulch could actually produce weed cover.

Polythene mulch - Polythene can be placed between rows. Crops are also grown through slits or

holes in thin plastic sheeting. This method is used in large-scale vegetable growing. However,

disposal of plastic mulch is a potential environmental problem.

Organic sheet mulch - Various products developed as a biodegradable alternative to plastic mulch.

Rock and gravel can also be used a mulch, especially in resorts.

Leaf mulch Cardboard mulch

A living mulch may also be considered a type of mulch, or as a mulch-like cover crop. This technique involves under sowing a main crop with a fast-growing cover crop that will provide weed suppression and other benefits associated with mulch. This is more relevant to permanent crops such as coconut

Student’s Manual For Level One and Two in Agriculture 61

Polythene mulch

Strip cropping

Growing crops in a systematic arrangement of strips across a field. Types of strip cropping include contour,

field or buffer.

Purpose • Reduce soil erosion from water

• Reduce the transport of sediment and other waterborne contaminants

• Reduce soil erosion from wind

• Protect growing crops from damage by windborne soil particles

• Improve water quality

Strip cropping is effective due to the precise arrangement of the alternating strips in the field. The crops are

arranged so that a strip of grass or close-grow-ing crop is alternated with a clean-tilled strip or a strip

with less protective cover. Generally, the strip widths are equal across the field. Where sheet and rill erosion is

a concern on sloping land, the strips are laid out on the contour or across the general slope. Where wind

erosion is a concern, the strips are laid out as closely perpendicular to the prevailing erosive wind direction as

possible. Strip cropping is a multipurpose practice that has one or more of the following effects:

• Reduced sheet and rill erosion

• Reduced wind erosion

• Increased infiltration and available soil moisture

• Reduced dust emissions into the air

• Improved water quality

• Improved visual quality of the landscape

• Improved wildlife habitat

• Improved crop growth

• Improved soil quality

This practice is used on

Limitation

Cropland and certain recreation and wildlife lands where field crops erosion from water or wind is a resource

concern. It is most effective when grasses and legumes can be rotated with crops requiring more intensive

cultivation. Strip cropping will not be effective when land slopes are longer than the critical slope length,

unless supported by other practices that reduce slope length below critical.

Student’s Manual For Level One and Two in Agriculture 62

Module 7

Soil fertility and plant nutrients

Photosynthesis

Photosynthesis is a fundamental biochemical

process in which higher plants, algae, and some

bacteria, convert the energy of sunlight into

chemical energy. The chemical energy is then used

to fix carbon into simple sugars that are converted

to glucose, the major food molecule of the cell.

Photosynthesis is the most important biochemical

pathway on earth. Photosynthetic organisms form

the bottom of the food chain. Energy sources such

as coal, oil and natural gas ultimately derive their

energy from photosynthesis. Photosynthesis is also

responsible for producing the oxygen that makes up

a large portion of the earth's air (atmosphere).

Plant Nutrition

Plant nutrition is the study of the chemical elements

that are necessary for plant growth. There are

several principles that apply to plant nutrition.

Some elements are essential, meaning that the

absence of a given mineral element will cause the

plant to fail to complete its life cycle; that the element cannot be replaced by the presence of another

element; and that the element is directly involved in plant metabolism. However, this principle does not

leave any room for the so-called beneficial elements, whose presence, while not required, has clear

positive effects on plant growth. Elements Needed

Plants require specific elements for growth and, in some cases, for reproduction as given in the list below.

Major chemical elements needed by plants are;

C = Carbon (C), Hydrogen (H), Oxygen (O), Phosphorus (P), Potassium (K), Nitrogen (N), Sulphur (S),

Calcium (C), Magnesium (Mg).

The minor chemical elements needed are;

Iron (Fe), Molybdenum (Mo), Boron (B), Copper (Cu), Manganese (Mn), Zinc (Zn), Chlorine (Cl)

These nutrients are further divided into the mobile and immobile nutrients. A plant will always supply

more nutrients to its younger leaves than its older ones, so when nutrients are mobile, the lack of nutrients

is first visible on older leaves. When a nutrient is less mobile, the younger leaves suffer because the

nutrient does not move up to them but stays lower in the older leaves. Nitrogen, phosphorus, and

potassium are mobile nutrients, while the others have varying degrees of mobility.

Each of the following nutrients is used in a different place for a different essential function.

Carbon

Student’s Manual For Level One and Two in Agriculture 63

Carbon is what most of the plant is made of. It forms the backbone of many plant molecules,

including starches and cellulose. Carbon is fixed through photosynthesis from the carbon dioxide

in the air and is a part of the carbohydrates that store energy in the plant.

Hydrogen

Hydrogen also is necessary for building sugars and building the plant. It is obtained from air and

liquid water.

Oxygen

Oxygen is necessary for cellular respiration. Cellular respiration is the process of generating

energy-rich adenosine triphosphate (ATP) via the consumption of sugars made in photosynthesis.

It is obtained from the air.

Phosphorus

Phosphorus is important in plant energy. As a component of ATP, phosphorus is needed for the

conversion of light energy to chemical energy (ATP) during photosynthesis. Phosphorus can also

be used to modify the activity of various enzymes. Phosphorus is important for plant growth and

flower and seed formation.

Potassium

Potassium regulates the opening and closing of the stoma. Since stomata are important in water

regulation, potassium reduces water loss from the leaves and increases drought tolerance.

Potassium deficiency may cause necrosis or interveinal chlorosis.

Nitrogen

Nitrogen is an essential component of all proteins, and as a part of DNA, it is essential for growth

and reproduction as well. Nitrogen deficiency most often results in stunting.

Sulphur

Sulphur is another important component of amino acids and proteins, and is therefore important

in plant growth.

Calcium

Calcium is a part of cell walls. It also regulates transport of other nutrients into the plant. Calcium

deficiency results in stunting.

Magnesium

Magnesium is an important part of chlorophyll, a critical plant pigment important in

photosynthesis. It is important in the production of ATP through its role as an enzyme cofactor.

Magnesium deficiency can result in interveinal chlorosis.

Iron

Iron is necessary for photosynthesis and is present as an enzyme cofactor in plants. Iron

deficiency can result in interveinal chlorosis and death of plant tissue.

Molybdenum

Molybdenum is a cofactor to enzymes important in building amino acids.

Student’s Manual For Level One and Two in Agriculture 64

Boron

Boron is important in sugar transport, cell division, and synthesizing certain enzymes. Boron

deficiency causes necrosis in young leaves and stunting.

Copper

Copper is important for photosynthesis. Symptoms for copper deficiency include chlorosis.

Manganese

Manganese is necessary for building the chloroplasts. Manganese deficiency may result in

coloration abnormalities, such as discolored spots on the foliage.

Zinc

Zinc is required in a large number of enzymes and plays an essential role in DNA transcription. A typical

symptom of zinc deficiency is the stunted growth of leaves, commonly known as "little leaf" and is

caused by the oxidative degradation of the growth hormone auxin. Additional elements include nickel and

silicon, whose requirements are vague for all but a very few select plants. Cobalt has proven to be

beneficial to at least some plants, but is essential in others, such as legumes where it is required for

nitrogen fixation. Vanadium may be required by some plants, but at very low concentrations. It may also

be substituting for molybdenum. Selenium and sodium may also be beneficial. Sodium can replace

potassium's regulation of stomatal opening and closing. Plant nutrition is a difficult subject to understand

completely, partially because of the variation between different plants and even between different species

or individuals of a given clone. Elements present at low levels may demonstrate deficiency, and toxicity is

possible at levels that are too high. Further, deficiency of one element may present as symptoms of

toxicity from another element, and vice-versa. Carbon and oxygen are absorbed from the air, while other

nutrients are absorbed from the soil. Green plants obtain their carbohydrate supply from the carbon

dioxide in the air by the process of photosynthesis. Of the above C, and O are not supplied to the plant as they are obtained from the environment. C from the carbon dioxide in the air (CO2), and O from oxygen (O2) in the air. Of the nutrients supplied N, P, and K are considered as the major nutrients, and the others as micro nutrients.

Under Maldivian conditions, Iron, Magnesium, Zinc, Copper, and Boron are also important and thus

supplied routinely. These are referred to as the secondary nutrients. The major functions of the macro and

secondary nutrients supplied to a plant are summarized below in Table

Major functions of macro and secondary nutrients

Student’s Manual For Level One and Two in Agriculture 65

Compost

Compost is the decomposed remnants of organic materials (those with plant and animal origins). Compost

is used in home gardening and agriculture as a soil amendment, and also in landscaping and in nurseries.

Composting is a means by which organic matter is recycled in its environment.

Composting is the common name for the decomposition of organic matter under aerobic conditions

(which means in the presence of Oxygen). The decomposition is performed primarily by microbes,

although larger creatures such as ants, nematodes, and worms also contribute. This decomposition occurs

naturally in all but the most hostile environments. Composting is the controlled decomposition of organic

matter. Rather than allowing nature to take its slow course, a composter provides an optimal environment

in which decomposers can thrive. To encourage the most active microbes, a compost pile needs the

correct mix of the following ingredients:

Carbon

Nitrogen

Oxygen (from the air)

Water

Decomposition happens even in the absence of some of these ingredients, but not as quickly or as

pleasantly. (For example, vegetables in a plastic bag will decompose, but the absence of air encourages

the growth of anaerobic microbes that produce disagreeable odors, degradation under anaerobic

conditions is called anaerobic digestion.)

There are a variety of methods of composting. In the home-garden this is often done in a composting bin

or a simple compost heap at a side of the garden. Although not directly relevant to farmers, there are also

industrial methods of composting such as In-vessel composting, Tunnel composting, and Windrow

composting which are used for large scale composting such as that used for the composting of urban

waste.

Compost ingredients Given enough time, all biodegradable material will compost. However, not all

compost base material are appropriate for home-garden composting. Most home-garden systems will not

reach high enough temperatures to kill pathogens.

Student’s Manual For Level One and Two in Agriculture 66

The goal in a compost pile is to provide a healthy environment and nutrition for the rapid decomposers,

the bacteria. The most rapid composting occurs with the ideal carbon to nitrogen ratio of between 25 and

30 to 1 by dry chemical weight. In other words, the ingredients placed in the pile should contain 25 to 30

times as much carbon as nitrogen. For example fresh leaves, average about 19 to 1 and dry leaves average

about 55 to 1. Mixing equal parts by volume approximates the ideal range.

High-carbon sources provide the cellulose needed by the composting bacteria for conversion to sugars

and heat, while high-nitrogen sources provide the most concentrated protein, which allow the compost

bacteria to thrive. Some ingredients with higher carbon content:

Dry leaves

Sawdust and wood chips

Some paper and cardboard (such as corrugated cardboard or newsprint with soy-based inks)

Some ingredients with higher nitrogen content:

Green plant material (fresh or wilted) such as crop residues, weeds , grass clippings

Fish waste

Animal manures (poultry manure)

Seaweeds

Fruit and vegetable trimmings

Compost can be produced at the farm level by mixing a variety of farm and household organic materials

such as dry/rotten leaves, weeds, seaweeds, coconut husks, green leaves, kitchen waste, banana stem and

fish waste.

Mixing the materials as they are added increases the rate of decomposition, but it can be easier to place

the materials in alternating layers, approximately 15 cm (6 in) thick, to help estimate the quantities.

Keeping carbon and nitrogen sources separated in the pile can slow down the process, but decomposition

will occur in any event.

Composting techniques There are two primary methods of aerobic composting:

Active (or hot) composting, which allows the most effective decomposing bacteria to thrive, kills

most pathogens and seeds, and rapidly produces usable compost

Passive (or cold) composting, which lets nature take its course in a more leisurely manner and

leaves many pathogens and seeds dormant in the pile

Home composters use a range of techniques varying from extremely passive composting (throw

everything in a pile in a corner and leave it alone for a year or two) to extremely active (monitoring the

temperature, turning the pile regularly, and adjusting the ingredients over time) and combinations of both.

An effective compost pile should be kept moist. This provides the moisture that all life needs to survive.

Bacteria and other microorganisms fall into a variety of groups in terms of what their ideal temperature is

and how much heat they generate as they do their work. Mesophilic bacteria enjoy midrange

temperatures, from about 20 to 40 °C (70 to 110 °F). As they decompose the organic matter, they generate

heat, and the inner part of a compost pile heats up the most.

The heap should be about 1 m (3 ft) wide, 1 m (3 ft) tall, and as long as is practicable. This provides a

suitable insulating mass to allow a good heat build-up as the material decays. The ideal temperature is

around 60 °C (140 °F), which kills most pathogens and weed seeds and while providing a suitable

environment for thermophilic (heat-loving) bacteria, which are the fastest acting decomposers. The centre

of the heap can get too warm, possibly hot enough to burn a bare hand. If this fails to happen, common

reasons include the following:

The heap is too wet, thus excluding the oxygen required by the compost bacteria

The heap is too dry, so that the bacteria do not have the moisture needed to survive and reproduce

There is insufficient protein (nitrogen-rich material)

Student’s Manual For Level One and Two in Agriculture 67

The solution is to add material, if necessary, and/or to turn the pile to aerate it. Depending on how quickly

the compost is required, the heap can be turned one or more times to bring the outer layers to the inside of

the heap and vice versa, as well as to aerate the mixture. Adding water at this time helps keep the pile

damp. One guideline is to turn the pile when the high temperature has begun to drop, indicating that the

food source for the fastest-acting bacteria (in the center of the pile) has been largely consumed. When the

temperature stops rising after the pile has been turned, there is no further advantage in turning the pile.

When all the material has turned into dark brown or nearly black crumbly matter, it is ready to use.

Some users like to put special materials and activators into their compost. Adding commercially available

Effective Microorganisms helps to keep the balance between "good" and "bad" bacteria. A light dusting

of agricultural lime (not on the animal manure layers) can curb excessive acidity that can slow down the

fermentation. Seaweed meal can provide a ready source of trace elements.

Two methods of preparing compost are given below;

Compost can be made in a heap on top of the soil, but this dries out too quickly. That is not good for the

organisms that make the humus. That is why it is better to make compost in a pit. To make a good

compost heap these are the things that should be done:

1. First dig a pit of 1.5m long and 1m wide. The pit should be about 50-60 cm deep. A farmer may need

to make 2 or more pits if he or she has a large vegetable garden.

2. Then make two heaps near the pit:

(a) One heap must be some good black soil that is collected from under trees.

If this cannot be obtained, use some very fine soil.

(b) The second heap must be some animal manure. Chicken manure is the best. If that is not

possible;

a. use cow dung or cow manure, or some goat manure.

b. use some fish scraps.

c. use some urea or ammonium sulphate fertilizer.

These heaps must be covered with coconut leaves to keep the sun and rain off them.

3. Gather a lot of dead leaves. Soft leaves are the best. Collect this into a big heap near the pit.

4. Also gather and add to the heap some leaves that contain a lot of nitrogen such as:

d. green leaves

e. leaves of leguminous plants

5. When all materials have been gathered, then fill the compost pit this way:

a. Put in a layer of plant material about 15cm deep at the bottom of the pit.

b. Over this sprinkle a thin layer of dark soil.

c. Then put a thin layer of animal manure. If there is no animal manure, sprinkle some urea or

ammonium sulphate lightly over the soil. Do not use much of this fertilizer; one match box full is enough.

d. If available, put a thin layer of compost on top of this. This compost could be obtained from an old

compost pit. The compost already contains many micro-organisms that will help speed up the composting

process.

e. Then put another layer of plant material.

f. On top of this put some more black soil.

g. Then sprinkle some more fertilizer or put a thin layer of manure.

h. Keep doing this until the pit is full and the heap is about 30-50 cm above the ground. (The heap

will soon start to sink down as the plant materials rots down).

i. Apply water over the heap until all the plant material will be wet right down to the bottom.

Student’s Manual For Level One and Two in Agriculture 68

j. Then cover the whole pit with dead coconut leaves to keep it moist and to keep the sun off it.

6. After 5-6 weeks, take the cover off the pit and dig all the compost out, mix it all up, and then put it

back again. It would be best if it is put back in another pit that has been dug nearby, so you can use the

old pit again for making new compost. This mixing helps to make the plant material rot down quicker and

lets air get into it too.

7. Then water it again and cover it again with coconut leaves.

8. Repeat this process again after another 5-6 weeks.

9. If fish waste is used, or some urea sprinkled on the heap, the compost will be ready in about 3 – 4

months. If only plant materials have been used with little or no urea or fish waste it can take up to 6

months before the compost is ready for use. If the weather has been quite dry it may even take a little

longer to be ready.

10. Once the compost is ready, it can be mixed with some soil (half of each) and used to make a garden

bed.

Another good way of making compost in smaller amounts is by using a 200 litre drum. This is especially

convenient around the house. Food scraps and other organic domestic waste could be used. It is also very

hygienic.

Take a clean drum, and cut open the top. This must be made into a lid that will fit into the drum and rest

on top of the compost.

Make three holes of about 1 cm diameter in the upper 1/3 part of the drum, and three holes in the lower

1/3 part of the drum. Space the holes evenly around the drum, at about 50 cm spacing.

Make another hole of 1 cm in the base of the drum. This will allow any liquids to seep from the drum.

Make an opening about 20 cm above the base of the drum. The opening should be about 65 cm high and

about 20 cm wide. This opening will allow to check the composting process. This opening should be kept

closed.

Place the drum on a stand or bricks of about 25 cm high. A tray or bucket could be placed underneath the

opening in the bottom of the drum to collect any liquid that seeps out from it. This liquid could be used as

a liquid fertilizer. Pour it around the plants. It can also be poured back into the drum.

It is best to work with two or three drums. The first one can be used for the initial compost, which is

sieved and put into the second drum for further composting. The third drum is used to store compost that

is ready for use.

It is best to cut the organic matter into small pieces before it is put into the first drum. If there is enough

material the drum can be filled at once. Otherwise the drum can be filled slowly.

If the drum is filled at once, it could be transferred to the second drum after about 4 to 5 days. It could be

left there for another 8 to 10 days. Then it is ready for use. If not needed for use at that time put it in the

third drum for storage.

If the drum is filled slowly, the farmer should wait for 4 to 5 days after it has been filled to the top. Then

the material could be taken out and sieved. The fine material can be transferred to the second drum. The

larger pieces and any not yet decomposed materials are put back in the first drum, and the process of

filling continued. When it is full, wait 4-5 days and repeat the process.

Student’s Manual For Level One and Two in Agriculture 69

Methods of Application Organic fertilizers can be used in the preparation of seed beds, in pockets or holes, and in furrows. During

land preparation it can be incorporated into the soil to increase its organic matter content. In seed bed

preparation a thin layer of well decomposed manure or compost can be evenly spread on the surface and

mixed into the soil with a hoe. In pockets or holes, when seedlings are transplanted manure or compost

could be mixed along with synthetic fertilizer in the soil of the hole

Crop rotation 11.2 Crop Rotation

The continuous raising of a particular crop on the same plot lowers the fertility and productivity. This

happens because:

(a) The same type of nutrient is continuously removed from the soil

(b) Certain pests and diseases of this crop increases rapidly

Crop rotation is a sequence in which different types of crops are grown in succession in the same plot of

land. The sequence is generally repeated over a period of time in a definite order. It helps to avoid the

buildup of pathogens and pests that often occurs when one species is continuously cropped. Crop rotation

also seeks to balance the fertility demands of various crops to avoid excessive depletion of soil nutrients.

A traditional component of crop rotation is the replenishment of nitrogen through the use of legumes in

sequence with other crops. Crop rotation can also improve soil structure and fertility by alternating deep-

rooted and shallow-rooted plants. Thus, crop rotation is done to:

(a) Maintain the fertility of the soil

(b) Increase crop yield

(c) Check the spread of diseases

(d) Reduce the pest population

(e) Add organic matter to the soil

(f) Make full use of the land

(g) Keep the land always under plant cover and thus prevent soil erosion

(h) Make available a wide variety of crops throughout the year

Legumes, plants of the family to which long beans belong, for instance, have nodules on their roots which

contain nitrogen-fixing bacteria. It therefore makes good sense agriculturally to alternate them with other

plants that require nitrates.

Crop rotation is also used to control pests and diseases that can become established in the soil over time.

Plants within the same family tend to have similar pests and pathogens. By regularly changing the

planting location, the pest cycles can be broken or limited. For example, root-knot nematode seen in the

figure is a serious problem for some plants in warm climates and sandy soils, where it slowly builds up to

high levels in the soil, and can severely damage plant productivity by cutting off circulation from the

plant roots. Growing a crop that is not a host for root-knot nematode for one season greatly reduces the

level of the nematode in the soil, thus making it possible to grow a susceptible crop the following season

without needing soil treatment.

This principle is of particular use in organic farming, where pest control must be achieved without

synthetic pesticides.

A general effect of crop rotation is that there is a geographic mixing of crops where a plot of land is

divided into four, and different crops are grown in the different sub-plots. The different crops can also

reduce the effects of adverse weather for the individual farmer and, by requiring planting and harvest at

different times, allow more land to be farmed with the same amount of equipment and labour.

Student’s Manual For Level One and Two in Agriculture 70

The choice and sequence of rotation crops depends on the nature of the soil, the climate, and rainfall

which together determine the type of plants that may be cultivated. Other important

aspects of farming such as crop marketing and economic factors must also be considered when choosing a

crop rotation. Due to the above it could be stated that crop rotation is successful if the following

principles are observed;

(a) Crops of the same family should not follow each other in the rotation

(b) Crops with shallow root systems should be followed by deep root crops

(c) A leguminous plant should always be included in the rotation

The figure below provides a suggested rotation that can be adopted in the Maldives. Additional vegetables

such as watermelon, pumpkin etc can be added to the cycle.

Once a crop from a certain group in the figure above has been grown, any crop from that same group

should not be grown on the same piece of land for some time.

Student’s Manual For Level One and Two in Agriculture 71

Module 8

Management of soil fertility

Use of legume plants

Legume plants are notable for their ability to fix atmospheric nitrogen thanks to a symbiotic

relationship with bacteria found in root nodules of these plants. The ability to form this

symbiosis reduces fertilizer costs for farmers and gardeners who grow legumes, and allows

legumes to be used in a crop rotation to replenish soil that has been depleted of nitrogen The

nitrogen fixation ability of legumes is enhanced by the availability of calcium in the soil and

reduced by the presence of ample nitrogen.

Legume seed and foliage have comparatively higher protein content than non-legume material,

probably due to the additional nitrogen that legumes receive through nitrogen-fixation symbiosis.

The high protein content makes them desirable crops in agriculture

Nutritional fact

Legumes contain relatively low quantities of the essential amino acid methionine To

compensate, some vegetarian cultures serve legumes along with grains, which are low in the

essential amino acid lysine which legumes contain. Thus a combination of legumes with grains

forms a well balanced diet for vegetarians. Common examples of such combinations are dal

with rice by Indians, and beans with corn tortillas with rice and peanut butter with wheat bread

(as sandwiches) in several other cultures, including Americans.

What is organic farming?

Organic farming is a system, which avoids or largely excludes the use of synthetic inputs (such as

fertilizers, pesticides, hormones, feed additives etc) and to the maximum extent feasible relies upon crop

rotations, crop residues, animal manures, off-farm organic waste, mineral grade rock additives and

biological system of nutrient mobilization and plant protection.

Is there a need to practice the organic farming?

With the increase in population our compulsion would be not only to stabilize agricultural production but

also to increase it further in sustainable manner. Excessive use over years of agro-chemicals like

pesticides and fertilizers may affect the soil health and lead to declining of crop yields and quality of

products. Hence, a natural balance needs to be maintained at all cost for existence of life and property.

The obvious choice would be judicious use of agro-chemicals and more and more use of naturally

occurring material in farming systems.

What are the benefits of organic farming?

1. It helps in maintaining environment health by reducing the level of pollution

2. It reduces human and animal health hazards by reducing the level of residues in the product.

3. It helps in keeping agricultural production at a higher level and makes it sustainable.

4. It reduces the cost of agricultural production and also improves the soil health

Student’s Manual For Level One and Two in Agriculture 72

5. It ensures optimum utilization of natural resources for short-term benefit and helps in conserving

them for future generation.

6. It not only saves energy for both animal and machine, but also reduces risk of crop failure.

7. It improves the soil physical properties such as granulation, and good tilth, good aeration, easy root

penetration and improves water-holding capacity.

8. It improves the soil’s chemical properties such as supply and retention of soil nutrients, and promotes

favorable chemical reactions.

Green manure and compost

What is green manuring?

Green manuring is the practice of growing a short duration, succulent and leafy legume crop and

ploughing the plants in the same field before they form seeds.

Green leaf manuring refers to adding the loppings from legume plants or trees to a field and then

incorporating them into the soil by ploughing

Sesbania, Crotalaria, ‘Pillipesara’, Cowpea etc are good for green manuring.

Glyricidia, Pongamia, Leucina are common green leaf manuring plants.

Compost is a rich source of organic matter. Soil organic matter plays an important role in sustaining soil

fertility, and hence in sustainable agricultural production. In addition to being a source of plant nutrient, it

improves the physico-chemical and biological properties of the soil. As a result of these improvements,

the soil:

(i) becomes more resistant to stresses such as drought, diseases and toxicity;

(ii) helps the crop in improved uptake of plant nutrients; and

(iii) possesses an active nutrient cycling capacity because of vigorous microbial activity.

These advantages manifest themselves in reduced cropping risks, higher yields and lower outlays on

inorganic fertilizers for farmers.

Why composting is necessary?

The rejected biological materials contain complex chemical compounds such as lignin, cellulose,

hemicellulose, polysaccharides, proteins, lipids etc.

These complex materials cannot be used as such as resource materials.

The complex materials should be converted into simple inorganic element as available nutrient.

The material put into soil without conversion will undergo conversion inside the soil.

This conversion process take away all energy and available nutrients from the soil affecting the

crop.

Hence conversion period is mandatory.

Advantages of Composting

Volume reduction of waste.

Final weight of compost is very less.

Student’s Manual For Level One and Two in Agriculture 73

Composting temperature kill pathogen, weed seeds and seeds.

Matured compost comes into equilibrium with the soil.

During composting number of wastes from several sources are blended together.

Excellent soil conditioner

Saleable product

Improves manure handling

Redues the risk of pollution

Pathogen reduction

Additional revenue.

Suppress plant diseases and pests.

Reduce or eliminate the need for chemical fertilizers.

Promote higher yields of agricultural crops.

Facilitate reforestation, wetlands restoration, and habitat revitalization efforts by amending

contaminated, compacted, and marginal soils.

Cost-effectively remediate soils contaminated by hazardous waste.

Remove solids, oil, grease, and heavy metals from stormwater runoff.

Capture and destroy 99.6 percent of industrial volatile organic chemicals (VOCs) in contaminated

air.

Provide cost savings of at least 50 percent over conventional soil, water, and air pollution

remediation technologies, where applicable.

The Benefits of Using Composts to Agriculture

Compost has been considered as a valuable soil amendment for centuries. Most people are aware

that using composts is an effective way to increase healthy plant production, help save money,

reduce the use of chemical fertilizers, and conserve natural resources. Compost provides a stable

organic matter that improves the physical, chemical, and biological properties of soils, thereby

enhancing soil quality and crop production. When correctly applied, compost has the following

beneficial effects on soil properties, thus creating suitable conditions for root development and

consequently promoting higher yield and higher quality of crops

Student’s Manual For Level One and Two in Agriculture 74

Module 9.1

Fertilizers Plant nutrition and soil plant system

Soil fertility is the capacity of the soil to supply the nutrients to the plants. If these nutrients are available

in the soil it enables the plants to grow vigorously and resist pest and diseases. A fertile soil therefore is

able to produce and sustain high crop yields. Poor unfertile soil on the other hand cannot provide adequate

amounts of nutrients to a plant. Hence, they are not very productive.

Fertilizers

Fertilizers are compounds given to plants with the intention of promoting growth; they are usually applied

either through the soil, for uptake by plant roots, or by foliar feeding, for uptake through leaves.

Fertilizers can be organic (composed of organic matter, i.e. carbon based), or inorganic (containing

simple, inorganic chemicals). They can be naturally-occurring compounds such as mineral deposits, or

manufactured through natural processes (such as composting) or chemical processes (such as the

production of urea). They are normally in the form of granules, pellets or crystals used in crop production.

However, liquid forms are also available, especially for foliar applications.

Fertilizers typically provide, in varying proportions, the three major plant nutrients, which are called the

macro nutrients, the secondary plant nutrients, and micronutrients ( or trace elements.)

Inorganic fertilizers

Inorganic fertilizers are also called mineral fertilizers.

Examples of naturally-occurring inorganic fertilizers include Chilean sodium nitrate, mined "rock

phosphate" as in Sri Lanka, and limestone (a calcium source, but mostly used to reduce soil

acidity).

Examples of manufactured or chemically-synthesized inorganic fertilizers include urea,

ammonium sulphate, potassium sulfate, and superphosphate, or triple superphosphate.

Categories of Inorganic Fertilizers

Inorganic fertilizer could be categorized as;

(a) Simple or straight fertilizers

(b) Compound fertilizers

(c) Complex fertilizers

Simple or Straight Fertilizers

This group of fertilizers contains one essential nutrient, e.g. nitrogen only

Compound Fertilizers

This group contains two or more essential nutrients in certain proportion e.g. phosphorus and potassium

Student’s Manual For Level One and Two in Agriculture 75

Complex Fertilizers

Contains the three major nutrients required by the plants in certain proportions. E.g. NPK 17:8:25,

contains 17 parts of nitrogen, 8 parts of phosphorous and 25 parts of potassium.

Agricultural versus Horticultural Fertilizers

In general, agricultural fertilizers contain only one or two macronutrients. Agricultural fertilizers are

intended to be applied infrequently and normally prior to seeding or concurrently with it. Examples of

agricultural fertilizers are granular triple superphosphate, potassium chloride, urea, and anhydrous

ammonia.

Horticultural or specialty fertilizers, on the other hand, are formulated from many of the same

compounds and some others to produce well-balanced fertilizers that also contain micronutrients. Some

materials, such as ammonium nitrate, are used minimally in large scale production farming. The 18-51-20

example above is a horticultural fertilizer formulated with high phosphorus to promote bloom

development in ornamental flowers, and may be appropriate for a resort, but not for normal crop

production. . Horticultural fertilizers may be water-soluble (instant release) or relatively insoluble

(controlled release). Controlled release fertilizers are also referred to as sustained release or timed release.

Many controlled release fertilizers are intended to be applied approximately every 3-6 months, depending

on watering, growth rates, and other conditions, whereas water-soluble fertilizers must be applied at least

every 1-2 weeks and can be applied as often as every watering if sufficiently dilute.

Inorganic fertilizers do not replace trace mineral elements in the soil which become gradually depleted by

crops grown there.

In some countries there is the public perception that inorganic fertilizers "poison the soil" and result in

"low quality" produce. However, there is very little (if any) scientific evidence to support these views.

When used appropriately, inorganic fertilizers enhance plant growth, the accumulation of organic matter

and the biological activity of the soil, while reducing the risk of water run-off, and soil erosion. The

nutritional value of plants for human consumption is typically improved when inorganic fertilizers are

used appropriately

Methods of Application

Incorporation into the soil: The fertilizers are spread on the soil and mixed by means of a hoe or any other

implement.

Broadcasting: The fertilizers are tossed all over the soil uniformly manually. One must be careful that the

fertilizer does not come in direct contact with the plants as fertilizers can burn them.

Band placement: The fertilizers are place on the soil around the plants or along the rows of crop.

Side dressing: The fertilizers are placed in small heaps at the side of the plants. These are then covered

with a thin layer of soil.

In irrigation water (fertigation): The fertilizers are dissolved in irrigation water and used in the field when

irrigating.

Foliar sprays: Soluble fertilizers are sprayed on the leaves of plants. It is common practice when using

micro nutrients on plants.

Time and Quantity of Application

Different crops need fertilizers at different period of growth according to their requirements. Fertilizers

are usually applied:

Student’s Manual For Level One and Two in Agriculture 76

(a) At planting time or before sowing of seeds

(b) During the early stages of life

(c) During the flushing, flowering and fruiting period

(d) When nutrient deficiency symptoms are observed regular fertilizer applications may have to be

increased.

Normally in the Maldivian soils this is very common. In such circumstances application of fertilizer

weekly or twice a week will be sufficient.

In general fertilizer is applied to the plants according to the following schedule

Guideline for fertilizing egg plants

Student’s Manual For Level One and Two in Agriculture 77

Guideline for fertilizing watermelon

Environmental Effects

Over-application of chemical fertilizers, or application of chemical fertilizers at a time when the ground is

waterlogged or the crop is not able to use the chemicals, can lead to surface runoff (particularly

phosphorus) or leaching into groundwater (particularly nitrates).

Storage and application of some fertilizers in some weather or soil conditions can cause emissions of the

greenhouse gas nitrous oxide (N2O). Ammonia gas (NH3) may be emitted following application of

inorganic fertilizers. Besides supplying nitrogen, ammonia can also increase soil acidity (lower pH).

For these reasons, it is recommended that knowledge of the nutrient content of the soil and nutrient

requirements of the crop are carefully balanced with application of nutrients in inorganic fertilizer

especially. This process is called nutrient budgeting. By careful monitoring of soil conditions, farmers can

avoid wasting expensive fertilizers.

In practice a combination of using both artificial and organic fertilizers is common. Normally this is

achieved by using inorganic fertilizers supplemented with the application of organics that are readily

available such as the return of crop residues.

Mixed fertilizers: are physical mixtures of straight fertilizers. They contain two or three primary plant

nutrients. Mixed fertilizers are made by thoroughly mixing the ingredients either mechanically or

manually.

According to the nutrients constitution, they are grouped as

1. Nitrogenous fertilizers

2. Phosphatic fertilizers

3. Potassic fertilizers

4. Complex or mixed fertilizers

5. Micronutrients

Student’s Manual For Level One and Two in Agriculture 78

Fertilizers can also be classified based on physical form as

1. Solid fertilizers

2. Liquid fertilizers

Solid fertilizers are in several forms viz.

1. Powder (single superphosphate),

2. Crystals (ammonium sulphate),

3. Prills (urea, diammonium phosphate, superphosphate),

4. Granules (Holland granules),

5. Supergranules (urea supergranules) and

6. Briquettes (urea briquettes)

Liquid fertilizers 1. Liquid form fertilizers are applied with irrigation water or for direct application.

2. Ease of handling, less labour requirement and possibility of mixing with herbicides has made the liquid

fertilizers more acceptable to farmers.

Nutrient supply is one of the most important factors influencing growth and productivity of the

horticultural crops. Adequate supply of plant nutrients is important to ensure efficient crop production.

Adding animal and vegetable manure to the soil to restore fertility is the practice from time immemorial.

As the use of the chemical fertilizers increased due to their large availability and easy-to-adopt technique,

organic manure application slowly declined. Since the nutrient turn-over in soil plant system is

considerably high under intensive farming, neither the chemical fertilizers nor the organic or biological

sources alone can achieve a sustainable production. Choice of manures and fertilizers and their

application at right quantity and time are important to get higher production

Complete fertilizer

Complete fertilizers are so called because they contain nitrogen, phosphorus and potassium, the Big 3 in

fertilizer ingredients. A fertilizer listed as "10-10-10," for instance, would be a complete fertilizer. But a

fertilizer listed as "10-0-10" would not be a complete fertilizer, the middle zero indicating the absence of

phosphorus in the fertilizer.

Student’s Manual For Level One and Two in Agriculture 79

Module 9.2

Deficiency symptoms of Macro and Micro nutrients

Nutrient deficiency

Soil fertility is the capacity of the soil to supply the nutrients to the plants. If these nutrients are available

in the soil it enables the plants to grow vigorously and resist pest and diseases. A fertile soil therefore is

able to produce and sustain high crop yields. Poor unfertile soil on the other hand cannot provide adequate

amounts of nutrients to a plant. Hence, they are not very productive.

A nutrient deficiency occurs when the nutrient is not in sufficient quantity to meet the needs of the

growing plant. This could be a common problem in the Maldives due to the poor condition of soil which

lacks adequate amounts of the macro, secondary and micro nutrients needed, or lacks the capacity to hold

these for a considerable period once applied to the soil.

Nutrient toxicity occur when a plant nutrient is in excess and decreases plant growth or quality. This

condition is generally not seen in the Maldives. However, it should be borne in mind that the excessive

use of fertilizer could be detrimental to the plant.

One way to understand the differences in nutrient deficiency symptoms of the plants is to know the

function and the relative mobility of the nutrient within the plant.

As indicated previously some nutrients, such as nitrogen, phosphorus, potassium, magnesium, chlorine

and zinc, can be easily transported within the plant from old plant parts to actively growing plant parts

such as young leaves. Other nutrients, such as sulfur, iron, copper, manganese, boron and calcium, are not

easily remobilized within the plant. Therefore, the deficiency of the mobile elements usually initially

occurs with older leaves while that of the immobile nutrients occurs with the young leaves or stem tips.

Five main types of deficiency or toxicity symptoms are observed

1 Chlorosis - yellowing of plant tissue due to limitations on chlorophyll synthesis.

This yellowing can be generalized over the entire plant, localized over entire leaves

or isolated between some leaf veins

(ie is inter-veinal chlorosis).

2. Necrosis - death of plant tissue sometimes in spots.

3. Accumulation of anthocynanin (plant pigment purplish in colour) resulting in a purple

or reddish color.

4. Lack of new growth.

5. Stunting or reduced growth. New growth continues but it is stunted or reduced compared

to normal plants

Student’s Manual For Level One and Two in Agriculture 80

Nutrient deficiency symptoms

Plant nutrient Type Visual symptoms

Nitrogen(N)

Deficiency

Light green to yellow appearance of leaves, especially older leaves; stunted growth; poor fruit development.

Excess

Dark green foliage which may be susceptible to lodging, drought, disease and insect invasion. Fruit and seed crops may fail to yield

Phosphorus(P)

Deficiency

Leaves may develop purple coloration. stunted plant growth and delay in plant development.

Excess

Excess phosphorus may cause micronutrient deficiencies, especially iron or zinc.

Potassium(K)

Deficiency

Older leaves turn yellow initially around margins and die irregular fruit development.

Excess

Excess potassium may cause deficiencies in magnesium and possibly calcium.

Magnesium (Mg)

Deficiency

Initial yellowing of older leaves between leaf veins spreading to younger leaves; poor fruit development and production.

Excess

High concentration tolerated in plant; however, imbalance with calcium and potassium may reduce growth.

Iron (Fe)

Deficiency

Initial distinct yellow (Fig. 8.2) or white areas between veins of young leaves leading to spots of dead leaf tissue.

Excess

Possible bronzing of leaves with tiny brown spots.

Zinc (Zn)

Deficiency

Inter-veinal yellowing on young leaves; reduced leaf size.

Excess

Excess zinc may cause iron deficiency in some plants.

Boron (B)

Deficiency

Death of growing points and deformation of leaves with areas of discoloration.

Excess

Leaf tips become yellow followed by necrosis. Leaves get a scorched appearance and later fall off.

Sulphur (S)

Deficiency

Initial yellowing of young leaves spreading to whole plant; similar symptoms to nitrogen deficiency but occurs on new growth.

Excess

Excess of sulphur may cause premature dropping of leaves.

Student’s Manual For Level One and Two in Agriculture 81

Manganese (Mn)

Deficiency

Inter-veinal yellowing or mottling of young leaves.

Excess

Older leaves have brown spots surrounded by a chlorotic circle or zone.

Chlorine (Cl)

Deficiency

Leaves are small and yellowish with spotty necrosis The chlorosis occurs on smooth flat depressions in between leaf blade and in more advanced cases bronzing on the upper side of the mature leaves.

Excess

Burning and dying of leaf and in severe conditions the death of the whole plant.

Calcium (Ca)

Deficiency

Reduced growth or death of growing tips; blossom-end rot of tomato; poor fruit development and appearance.

Excess

Excess calcium may cause deficiency in either magnesium or potassium

Nutrient Toxicity symptoms

Nutrient deficiency symptoms may be classified as follows:

1. Complete crop failure at the seedling stage.

2. Severe stunting of plants.

3. Specific leaf symptoms appearing at varying times during the season.

4. Internal abnormalities such as clogged conductive tissues.

5. Delayed or abnormal maturity.

6. Obvious yield differences, with or without leaf symptoms.

7. Poor quality of crops, including differences in protein, oil, or starch content, and storage quality.

8. Yield differences detected only by careful experimental work.

9. Chlorosis - yellowing of plant tissue due to limitations on chlorophyll synthesis. This yellowing

can be generalized over the entire plant, localized over entire leaves or isolated between some leaf

veins (i.e. interveinal chlorosis).

10. Necrosis - death of plant tissue sometimes in spots.

11. Accumulation of anthocynanin resulting in a purple or reddish color.

12. Lack of new growth.

13. Stunting or reduced growth - new growth continues but it is stunted or reduced compared to

normal plants.

Student’s Manual For Level One and Two in Agriculture 82

Module 9.3

Nitrogen Role of nitrogen in plants

Plants are surrounded by the nitrogen (N) in our atmosphere. Every acre of the earth’s

surface is covered by thousands of pounds of this essential nutrient, but because

atmospheric gaseous nitrogen is present as almost inert nitrogen (N2) molecules, this

nitrogen is not directly available to the plants that need it to grow, develop and reproduce. Despite

nitrogen being one of the most abundant elements on earth,nitrogen deficiency is probably the most

common nutritional problem affecting plants worldwide. Healthy plants often contain 3-4% nitrogen in their aboveground tissues. These are much higher

concentrations than those of any other nutrient except carbon, hydrogen and oxygen,

nutrients not of soil fertility management concern in most situations. Nitrogen is an

important component of many important structural, genetic and metabolic compounds in

plant cells. It is a major component of chlorophyll, the compound by which plants use

sunlight energy to produce sugars from water and carbon dioxide (i.e. photosynthesis).

It is also a major component of amino acids, the building blocks of proteins. Some

proteins act as structural units in plant cells while others act as enzymes, making

possible many of the biochemical reactions on which life is based. Nitrogen is a

component of energy-transfer compounds, such as ATP (adenosine triphosphate) which

allow cells to conserve and use the energy released in metabolism. Finally, nitrogen is a

significant component of nucleic acids such as DNA, the genetic material that allows

cells (and eventually whole plants) to grow and reproduce. Nitrogen plays the same

roles (with the exception of photosynthesis) in animals, too. Without nitrogen, there

would be no life as we know it.

Plants absorb nitrogen from the soil as both NH4+ and NO3- ions, but because

nitrification is so pervasive in agricultural soils, most of the nitrogen is taken up as

nitrate. Nitrate moves freely toward plant roots as they absorb water. Once inside the

plant NO3- is reduced to an NH2 form and is assimilated to produce more complex

compounds. Because plants require very large quantities of nitrogen, an extensive root

system is essential to allowing unrestricted uptake. Plants with roots restricted by

compaction may show signs of nitrogen deficiency even when adequate nitrogen is

present in the soil.

Methods of nitrogen fixation

Nitrogen fixation generally refers to the natural process, either biological or abiotic, by which nitrogen

(N2) in the atmosphere is converted into ammonia This process is essential for life because fixed nitrogen

is required to biosynthesize the basic building blocks of life, e.g. nucleotides for DNA and amino acid for

proteins Formally, nitrogen fixation also refers to other abiological conversions of nitrogen, such as its

conversion to nitrogen dioxide

Nitrogen fixation is utilized by numerous prokaryotes including bacteria, actinobacteria and certain types

of anaerobic bacteria. Microorganisms that fix nitrogen are called diazotrophs. Some higher plants, and

some animals have formed associations (symbiosis) with diazotrophs. Nitrogen fixation also occurs as a

result of non-biological processes. These include lightning and combustion Biological nitrogen fixation

was discovered by the Dutch microbiologist Martinus Beijerinck

Student’s Manual For Level One and Two in Agriculture 83

Biological nitrogen fixation

Biological nitrogen fixation (BNF) occurs when atmospheric nitrogen is converted to ammonia by an

enzyme called nitrogenase The formula for BNF is:

N2 + 6 H+ + 6 e− → 2 NH3

Plants that contribute to nitrogen fixation include the legume family – Fabaceae – with taxa such as

clover, soybeans etc They contain symbiotic bacteria called Rhizobia within nodules in their root

system producing nitrogen compounds that help the plant to grow and compete with other plants. When the plant dies, the fixed nitrogen is released, making it available to other plants and this helps to

fertilize the soil The great majority of legumes have this association, but a few genera do not. In many

traditional and organic farming practices, fields are rotated through various types of crops, which usually

includes one consisting mainly or entirely of clover or buckwheat which were often referred to as "green

manure

Non-leguminous nitrogen-fixing plants

Although by far the majority of nitrogen-fixing plants are in the legume family Fabaceae there are a few

non-leguminous plants that can also fix nitrogen. These plants, referred to as "actinorhizal plants ",

consist of 22 genera of woody shrubs or trees scattered in 8 plant families. The ability to fix nitrogen is

not universally present in these families. For instance, of 122 genera in the Rosaceae, only 4 genera are

capable of fixing nitrogen.

Nitrogen fixation by cyanobacteria

Cyanobacteria inhabit nearly all illuminated environments on Earth and play key roles in the carbon and

nitrogen cycle of the biosphere. Generally, cyanobacteria are able to utilize a variety of inorganic and

organic sources of combined nitrogen, like nitrate,nitrite,ammonium,urea or some amino acid Several

cyanobacterial strains are also capable of diazotrophic growth.

Chemical nitrogen fixation

Nitrogen can also be artificially fixed for use in fertilizers, explosives, or in other products. The most

common method is the Haber process .Artificial fertilizer production is now the largest source of human-

produced fixed nitrogen in the earth ecosystem

The Haber process requires high pressures (around 200 atm) and high temperatures (at least 400 °C),

routine conditions for industrial catalysis. This highly efficient process uses natural gas as a hydrogen

source and air as a nitrogen source.

Nitrogen cycle

Nitrogen Fixation The chemical nature of nitrogen gas (with triple bonds), makes it unusable in its elemental form. Thus,

atmospheric nitrogen is fixed as ammonium by means of lightening (natural fixation), microbes

(biological fixation) and industrial fixation (under high pressure and temperature). Nitrogen is also

converted into nitrogen oxides (NOx) by burning fossil fuels.

Student’s Manual For Level One and Two in Agriculture 84

Nitrogen Assimilation Soil nitrogen is contributed by application of plant manures and fertilizers. Nitrogen from the soil

reservoir is absorbed by some species of plants in the chemical form of ammonium ions or nitrate ions.

Animals, on the other hand, derived their nitrogen requirements by consumption of plants and other

organic matter.

Nitrogen Mineralization Also known a ammonification, organic form of nitrogen from the animal wastes, death and decayed living

organisms is converted into inorganic form. Over here, decomposers (bacteria and fungi) act on the

decayed organic matter containing nitrogen and convert it into ammonium (NH4+).

Nitrification

By the process of nitrification, the ammonium NH4+ is converted into nitrates NO3

- that are assimilated by

plants. First, ammonium is oxidized into nitrites (NO2-), which are further oxidized to form nitrates (NO3

-

). In this nitrogen cycle step, oxygen is essential for conversion of the nitrates by nitrifying bacteria

(mostly soil bacteria).

Denitrification

Denitrification is the process, wherein nitrates are converted to the molecular nitrogen form (N2) in an

anaerobic condition by the process of reduction. Heterotrophic bacteria and autotrophic denitrifiers are

responsible for carrying out this nitrogen cycle step. This is the end of nitrogen cycle, in which the

molecular nitrogen is returned back to the atmosphere and soil.

Carbon dioxide Cycle

Student’s Manual For Level One and Two in Agriculture 85

Organic chemicals are made from carbon more than any other atom, so the Carbon Cycle is a very

important one. Carbon between the biological to the physical environment as it moves through the carbon

cycle.

Earth's atmosphere contains 0.035% carbon dioxide, CO2, and the biological environment depends upon

plants to pull carbon into sugars, proteins, and fats.

Using photosynthesis, plants use sunlight to bind carbon to glucose, releasing oxygen (O2)in the process.

Through other metabolic processes, plants may convert glucose to other sugars, proteins, or fats. Animals

obtain their carbon by eating and digesting plants, so carbon moves through the biotic environment

through the trophic system. Herbivore eats plants, but are themselves eaten by carnivores

Carbon returns to the physical environment in a number of ways. Both plants and animals respire, so they

release CO2 during respiration. Luckily for animals, plants just happen to consume more CO2 through

photosynthesis than they can produce another route of CO2 back to the physical environment occurs

through the death of plants and animals. When organisms die, decomposers consume their bodies. In the

process, some of the carbon returns to the physical environment by way of fossilization. Some of it

remains in the biological environment as other organisms eat the decomposers. But by far, most of the

carbon returns to the physical environment through the respiration of CO2.

Student’s Manual For Level One and Two in Agriculture 86

Module 10.1

Method of cultivation Mixed farming

Mixed farming is the combining of two independent agricultural enterprises on the same farm. A typical

case of mixed farming is the combination of crop enterprise with dairy farming or in more general terms,

crop cultivation with livestock farming. Mixed farming may be treated as a special case of diversified

farming. This particular combination of enterprises, support each other and add to the farmer’s

profitability.

One of the real advantages of mixed farming is in environmental sustainability.

Mixed farming is probably the most benign agricultural production system from an environmental

perspective because it is, at least partially, a closed system. The waste products of one enterprise (crop

residues), which would otherwise be loaded on to the natural resource base, are used by the other

enterprise, which returns its own waste products (manure) back to the first enterprise. Because it provides

many opportunities for recycling and organic farming and for a varied, more attractive landscape, mixed

farming is the favorites system of many agriculturalists and environmentalists.

In many situations crop and livestock production is largely in balance with nature. There are important

exceptions, such as some mixed farming systems of the tropical highlands of Asia and Central Africa

which, partly because of overgrazing, are amongst the most eroded and degraded systems of the world.

On the other end of the development spectrum, heavy use of feed and fertilizer in the industrial world and

in some of the fast growing economies of East Asia, has led to nutrient loading, habitat destruction and

water pollution. In this context, it has to be remembered that integrating crops and livestock neither

generates new nutrients (with the exception of nitrogen fixation by leguminous plants) nor reduces

nutrient surpluses.

Environmentally, mixed farming systems:

• maintain soil fertility by recycling soil nutrients and allowing the introduction and use of rotations

between various crops and forage legumes and trees, or for land to remain fallow and grasses and shrubs

to become reestablished;

• maintain soil biodiversity, minimize soil erosion, help to conserve water and provide suitable habitats

for birds;

• make the best use of crop residues. When they are not used as feed, stalks may be incorporated directly

into the soil, where, for some time, they act as a nitrogen trap, exacerbating deficiencies. In the tropical

semi-arid areas, termite action results in loss of nutrients before the next cropping season. Burning, the

other alternative, increases carbon dioxide emissions; and

• allow intensified farming, with less dependence on natural resources and preserving more biodiversity

than would be the case if food demands were to be met by crop and livestock activities undertaken in

isolation.

Student’s Manual For Level One and Two in Agriculture 87

Inter cropping

Intercropping is the practice of growing two or more crops in close proximity. The most common goal

of intercropping is to produce a greater yield on a given piece of land by making use of resources that

would otherwise not be utilized by a single crop. Careful planning is required, taking into account the soil,

climate crops, and varieties it is particularly important not to have crops competing with each other for

physical space,nutrients,water or sunlight Examples of intercropping strategies are planting a deep-rooted

crop with a shallow-rooted crop, or planting a tall crop with a shorter crop that requires partial shade.

When crops are carefully selected, other agronomic benefits are also achieved. Lodging-prone plants,

those that are prone to tip over in wind or heavy rain, may be given structural support by their companion

crop. Delicate or light sensitive plants may be given shade or protection, or otherwise wasted space can be

utilized. An example is the tropical multi-tier system where coconut occupies the upper tier, banana the

middle tier, and pineapple, ginger or leguminous fodder, medicinal or aromatic plants occupy the lowest

tier.

Intercropping of compatible plants also encourages biodiversity by providing a habitat for a variety of

insects and soil organisms that would not be present in a single crop environment. This biodiversity can in

turn help to limit outbreaks of crop pests by increasing the diversity or abundance of natural enemies,

such as spiders or parasitic wasps increasing the complexity of the crop environment through

intercropping also limits the places where pests can find optimal foraging or reproductive conditions.

The degree of spatial and temporal overlap in the two crops can vary somewhat, but both requirements

must be met for a cropping system to be an intercrop. Numerous types of intercropping, all of which vary

the temporal and spatial mixture to some degree, have been identified These are some of the more

significant types:

Mixed intercropping, as the name implies, is the most basic form in which the component crops

are totally mixed in the available space.

Row cropping involves the component crops arranged in alternate rows. This may also be called

alley cropping. A variation of row cropping is strip cropping, where multiple rows, or a strip, of

one crop are alternated with multiple rows of another crop.

Intercropping also uses the practice of sowing a fast growing crop with a slow growing crop, so

that the fast growing crop is harvested before the slow growing crop starts to mature. This

obviously involves some temporal separation of the two crops.

Further temporal separation is found in relay cropping, where the second crop is sown during the

growth, often near the onset of reproductive development or fruiting of the first crop, so that the

first crop is harvested to make room for the full development of the second.

When two or more crops are growing together, each must have adequate space to maximize

cooperation and minimize competition between them. To accomplish this, four things need to be

considered: 1) spatial arrangement, 2) plant density, 3) maturity dates of the crops being grown,

and 4) plant architecture.

Spatial arrangement

There are at least four basic spatial arrangements used in intercropping. Most practical systems

are variations of these.

Student’s Manual For Level One and Two in Agriculture 88

Row intercropping—growing two or more crops at the same time with at least one crop planted in

rows

Strip intercropping—growing two or more crops together in strips wide enough to permit

separate crop production using machines but close enough for the crops to interact.

Mixed intercropping—growing two or more crops together in no distinct row arrangement

Relay intercropping—planting a second crop into a standing crop at a time when the standing

crop is at its reproductive stage but before harvesting.

Plant Density

To optimize plant density, the seeding rate of each crop in the mixture is adjusted below its full

rate. If full rates of each crop were planted, neither would yield well because of intense

overcrowding. By reducing the seeding rates of each, the crops have a chance to yield well within

the mixture. The challenge comes in knowing how much to reduce the seeding rates. For

example, if you are planning to grow corn and cowpeas, and you want mostly peas and only a

little corn, it would be easy to achieve this.

The corn-seeding rate would be drastically cut (by 80% or more), and the pea rate would be near

normal. The field should produce near top yields of peas even from the lower planting rate and

offer the advantage of corn plants for the pea vines to run on. If you wanted equal yields from

both peas and corn, then the seeding rates would be adjusted to produce those equal yields

Maturity dates

Planting intercrops that feature staggered maturity dates or development periods takes advantage

of variations in peak resource demands for nutrients, water, and sunlight. Having one crop mature

before its companion crop lessens the competition between the two crops. An aggressive climbing

bean may pull down corn or sorghum growing with it and lower the grain yield. Timing the

planting of the aggressive bean may fix the problem if the corn can be harvested before the bean

begins to climb. A common practice in the old southern U.S. cotton culture was to plant velvet

beans or cowpeas into standing corn at last corn cultivation. The corn was planted on wide 40-

inch rows at a low plant population, allowing enough sunlight to reach the peas or beans. The

corn was close enough to maturity that the young legumes did not compete When the corn was

mature, the beans or peas had corn stalks to climb on. The end result was corn and beans that

would be hand harvested together in the fall. Following corn and pea harvest, cattle and hogs

would be turned into the field to consume the crop fodder.

Selecting crops or varieties with different maturity dates can also assist staggered harvesting and

separation of grain commodities. In the traditional sorghum/pigeonpea intercrop, common in

India, the sorghum dominates the early stages of growth and matures in about four months.

Following harvest of the sorghum, the pigeon pea flowers and ripens. The slow-growing

pigeonpea has virtually no effect on the sorghum yield.

Student’s Manual For Level One and Two in Agriculture 89

Plant Architecture

Plant architecture is a commonly used strategy to allow one member of the mix to capture

sunlight that would not otherwise be available to the others widely spaced corn plants growing

above an understory of beans and pumpkins is a classic example

Types of intercropping practices

Mixed or multiple cropping is the cultivation of two or more crops simultaneously on the same

field without a row arrangement

Relay cropping is the growing of two or more crops on the same field with the planting of the

second crop after the first one

Row intercropping is the cultivation of two or more crops simultaneously on the same field with a

row arrangement Strip cropping is the cultivation of different crops in alternate strips of uniform width and on the

same field. It has two types; contour strip cropping and field strip cropping. Contour strip cropping

follows a layout of a definite rotational sequence and the tillage is held closely to the exact contour

of the field. Field strip cropping has strips with uniform width that follows across the general slope

of the land

Advantages

Reduces the insect/mite pest populations because of the diversity of the crops

grown. When other crops are present in the field, the insect/mite pests are

confused and they need more time to look for their favorite pants

Reduces the plant diseases. The distance between plants of the same species is

increased because other crops (belonging to a different family group) are planted

in between

Reduces hillside erosion and protects topsoil, especially the contour strip

cropping

Attracts more beneficial insects, especially when flowering crops are included

the cropping system

Minimizes labor cost on the control of weeds. A mixture of various crops gives

often a better coverage of the soil leaving less space for the development of

weeds

Utilizes the farm area more efficiently

Results in potential increase for total production and farm profitability than when

the same crops are grown separately

Provides 2 or more different food crops for the farm family in one cropping

season

Mixed Cropping

Mixed cropping is growing of two or more crops simultaneously on the same piece of land. It is also

known as multiple cropping. This type of cropping leads to an improvement in the fertility of the soil and

hence, increase in crop yield because when the two crops are properly chosen the products and refuse

from one crop plant help in the growth of the other crop plant and vice-versa. Mixed cropping is an

insurance against crop failure due to abnormal weather conditions.

Student’s Manual For Level One and Two in Agriculture 90

By planting one line of one crop, then a line of another crop, both crops can get better. In one line a

leguminous crop and in another line the crop which is to be planted. So, if one crop takes the nitrogen

from the soil, the another leguminous crop fixes the crop. The nitrogen is fixed in the root nodules of the

leguminous plants in the form of nitrates (soluble form of nitrogen) . Hence, the fertility of the soil gets

maintained. This helps the farmers to produce more and more crops without the nitrogen being depleted

from the soil.

Mixed cropping is not the same as crop rotation in crop rotation you plant different crops in the same field

in different years. Some plants add nitrogen to the soil some take it out. If you would plant the same crop

year after year, you wear out your soil.

Multiple-cropping patterns are described by the number of crops per year and the intensity of crop

overlap. Double cropping or triple cropping signifies systems with two or three crops planted sequentially

with no overlap in growth cycle. Intercropping indicates that two or more crops are planted at the same

time, or at least planted so that significant parts of their growth cycles overlap. Relay cropping describes

the planting of a second crop after the first crop has flowered; in this system there still may be some

competition for water or nutrients. When a crop is harvested and allowed to regrow from the crowns or

root systems, the term ratoon cropping is used. Sugarcane, alfalfa, and sudangrass are commonly

produced in this way, while the potential exists for such tropical cereals as sorghum and rice. Mixed

cropping, strip cropping, associated cropping, and alternative cropping represent variations of these

systems. See also Agriculture; Agronomy.

Row inter cropping

Wide-row intercropping is practiced principally for the production of tree products (e.g., poles, timber,

fruits). Wide spacings between rows (e.g., 10-20 meters) are used to avoid negative impact on the

associated crops because the trees are grown to large sizes. Planting trees in wide rows divides the farm

into a series of narrow fields with trees bordering each field. It is recommended that the trees be planted

on contours. Trees can initially be planted fairly close within the rows (e.g., 1-2 meters), and later thinned

as the trees reach usable sizes (ex., small poles)

A typical indigenous practice is to allow some trees which have come up naturally to grow in a scattered

arrangement in the field. This is basically the same as wide-row intercropping. However, uniform spacing

and contour planting ensures uniform treatment (microclimatic), ease in mechanized operations, and

enables conversion to alternate crops without necessitating removal of the trees

In wide-row intercropping, tree canopies can be managed through periodic pollarding, or other forms of

canopy management, to reduce shade competition. This should coincide with the cropping season to

reduce shade.

Important genera for wide-row intercropping are generally similar to those recommended for windbreaks.

Again, final species choice should be largely determined by what tree product the individual farmer wants

Student’s Manual For Level One and Two in Agriculture 91

Module 10.2

Present Cropping Patterns and uses

Classification of Herbicides

An herbicide, commonly known as a weed killer, is a type of pesticide used to kill unwanted

plants Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some

of these act by interfering with the growth of the weed and are often synthetic "imitations" of

plant hormones . Herbicides used to clear waste ground, industrial sites, railways and railway

embankments are non-selective and kill all plant material with which they come into contact. Smaller

quantities are used in forestry, pasture systems, and management of areas set aside as wildlife habitat

Some plants produce natural herbicides, such as the genus walnut the study of such natural herbicides,

and other related chemical interactions, is called allelopathy.

Herbicides are widely used in agriculture and in landscape turf management. In the U.S., they account for

about 70% of all agricultural pesticide use.

A herbicide is any chemical that kills the plants or inhibits their growth. Selective herbicides remove

certain weeds from certain crops. The electivity is not absolute, but is governed by the amount of the

chemical applied, the way it is applied, the degree of wetting of the foliage, the of rainfall following the

application, the tolerance of different plants to s specific chemical and the differences in the growth habits

of the crops and the weeds. Non-selective herbicides remove a wide range of vegetation, although plants

differ in their susceptibility to any particular chemical. These two major groups of herbicides are further

classified as given below,

Selective herbicides

Selective herbicides have been used extensively since the introduction of 2,4-D in the late '40s. They have

Been one of the miracles of modem agriculture, releasing thousands of people from the drudgery of hand

Weeding. A selective herbicide is one that kills or retards the growth of an unwanted plant or "weed"

while Causing little or no injury to desirable species. 2,4-D used in turf will kill many of the broadleaf

weeds that Infest turf while not significantly injuring the turf grass. But selectivity is a fickle, dynamic

process. Excessive Rates of 2,4-D applied to stressed turf grass may injure the turf. Selectivity has always

depended on proper herbicide application. Normally herbicides work selectively within a given rate of

application. Too little herbicide and no weed control, too much and crop injury may Occur. But

selectivity is more complex than this. It is a dynamic process that involves the interaction of the plant, the

herbicide, and the environment.

There are several basic types of herbicides, each targeting certain plant pests (weeds, grasses.) Pre-

emergent herbicides are used to stop the germination of plant seeds. Post emergent herbicides can be

selective or non-selective. Products such as Roundup can be considered total vegetation, non selective

and post emergent.

Student’s Manual For Level One and Two in Agriculture 92

A non-selective herbicide tries to kill most plants while a selective herbicide is designed to kill specific

types of plants, usually grasses or broad leaf weeds. Total vegetation products (listed on this page) are

considered soil sterilizers, killing all plant nutrients in the soil and preventing any vegetation from

surviving. When spraying herbicides on plants, a surfactant can be used to increase the efficiency of

herbicides.

Some of the most common herbicides in this category are ones that kill broad-leafed plants while leaving

grass species unharmed. These kinds of selective herbicides are extremely important in crop cultivation,

and are also used to maintain lawns and turf. A widely used example of this type of herbicide is 2,4-

dichlorophenoxyacetic acid (2,4-D). It has been in common use since the 1940s, and is still important in

agriculture today. While 2,4-D has good selectivity, crop plants can still be damaged by it if too much of

the chemical is applied.

Grass selective herbicides are a type of selective herbicide that kills grasses, but allows the continued

growth of broad-leafed plants. Fluazifop is one example. These types of herbicides are important for the

cultivation of broad-leafed crops such as peas and soya beans, and for controlling grass growth in

orchards and vineyards.

Herbicides are quite specific in their structures as to whether or not herbicidal activity is possible. Slight

Changes in conformation or structure will alter herbicidal activity. Trifluralin and benefin differ in only a

Methyl group moved from one side of the molecule to the other, yet trifluralin is about twice as active as

Benefin. Esters of peony (MCPP etc.) acids are usually much more active than are amines. The manner of

Formulation of an herbicide can affect its selectivity. The most extreme case of this might be granular

Formulations which bounce off desirable plants to reach the soil where they then limit germinating weeds.

Other substances known as adjuvants or surfactants are often added to improve the application properties

of a liquid formulation and increase activity. The manner in which an herbicide is applied can affect its

selectivity. When a broad-spectrum post emergence herbicide like glyphosate is applied as a shielded,

directed, or wicked application within a

Susceptible crop, susceptible foliage is avoided and selectivity is achieved with this normally non

selective herbicide.

Herbicides can be grouped into families based on the type of action that they have within affected plants

(Their mode of action). Herbicides which affect similar sites or processes within affected plants produce

Similar injury symptoms. The herbicide families listed below are grouped on the basis of how they affect

Plants:

1. The Growth Regulator Herbicides (2,4-D, MCPP, dicamba, and triclopyr). These are mostly foliar

applied herbicides which are systemic and translocate in both the xylem and phloem of the plant. They

mimic natural plant auxins, causing abnormal growth and disruption of the conductive tissues of the plant.

Injury from this family of herbicides consists of twisted, malformed leaves and stems.

2. The inhibitors of amino acid synthesis (glyph sate, halosulfuron, imazethapyr, and sulfometuron). Both

Foliar and soil applied herbicides are in this family. Glyph sate translocates in the phloem with

Photosynthetic produced in the leaves. Others in this family move readily after root or foliar absorption.

These herbicides inhibit certain enzymes critical to the production of amino acids. Amino acids are the

Building blocks of proteins. Once protein production stops, growth stops. Symptoms are stunting and

Symptoms associated with lack of critical proteins.

3. Cell membrane disrupters - with soil activity (oxyfluorfen, lacto fen, and acifluorfen). Soil and foliar

Applied with limited movement in soil. These herbicides enter the plant through leaves, stems, and roots,

But are limited in their movement once they enter the plant. Membrane damage is due to lipid

Student’s Manual For Level One and Two in Agriculture 93

Per oxidation. Symptoms are necrosis of leaves and stem.

4. Lipid biosynthesis inhibitors (diclofop, fluazifop, sethoxydim, and clethodim). Foliar applied Diclofop

has both soil and foliar activity. Herbicides in this family move in both the xylem and phloem of the plant

and inhibit enzymes critical in the production of lipids. Lipids are necessary to form plant membranes

which are essential to growth and metabolic processes. Symptoms include stunting and death of tissue

within the growing points of plants.

5. Pigment inhibitors (norflurazon, fluridone, and amitrol). Soil applied and moves in the xylem except

amitrol, which moves in both phloem and xylem. These herbicides inhibit carotinoid biosynthesis, leaving

Chlorophyll unprotected from photo oxidation. This results in foliage which lacks color. Symptoms

Include albino or bleached appearance of foliage.

6. Growth inhibitors of shoots (thiocarbamate herbicides including: EPTC, cycloate, pebulate, and

Molinate). Soil applied and somewhat volatile, requiring incorporation. Enter the plant through the roots

and translocated through the xylem with the transpiration stream to the growing points in the shoot. Mode

of action is unclear, but affects developing leaves in growing points of susceptible plants. Symptoms

include stunting and distortion of seedling leaves.

7. Herbicides which disrupt cell division (trifluralin, DCPA, dithiopyr, oryzalin, pronamide,

pendimethalin, and napropamide). All are soil applied, with limited movement in the soil. Absorbed

through roots or emerging shoot tips. Once absorption takes place, movement is limited (site of action is

near the site of absorption). These herbicides inhibit cell division or mitosis, except pronamide and

napropamide which stop cell division before mitosis. Symptoms include stunting and swollen root tips.

8. Cell membrane disrupters - no soil activity (parquet, diquat, glufosinate, acids, oils, soaps). These

herbicides are foliar applied with no soil activity. They enter the plant through the leaves and stems and

do not move significantly within the plant once absorbed. These herbicides either act directly on cell

membranes (acids, soaps. oils) or react with a plant process to form destructive compounds which result

in membrane damage. Symptoms include rapid necrosis of the leaves and stem.

9. Inhibitors of photosynthesis (atrazine, simazine, metribuzin, cyanazine, prometryn, diuron, linuron,

tebuthiuron, and bromacil). These are soil applied herbicides; however, all except simazine also have

foliar activity. They move readily in the plant in the xylem with the transpiration stream where they

concentrate in the leaves at the site of photosynthesis. Once there they block the electron transport system

of photosynthesis, causing a build up of destructive high energy products which destroy chlorophyll and

ultimately the leaf tissues. Symptoms include chlorotic (yellowed) leaves which become necrotic.

A. FOLIAGE APPLICATIONS. These applications are made to the leaves of growing

plants, usually as sprays, but in a few cases as dust applications.

(i) Contact herbicides. Contact herbicides kill only the plant or the portions of the plant that

actually come into contact with the chemical. The herbicide to be effective must cover the

foliage. Selectivity is dependent upon the differential wetting, differences in forms of the

plants, and also upon the placement of the spray. Some examples are dicryl, potassium

cyanate, selective weed-oil (carrot-oil), sodium arsenate, Solan, Propanil and sulphuric acid.

(ii) Translocated herbicides. Translocated herbicides move within the plant, a properly that

makes them effective in destroying the roots of perennial weeds. A low-volume application

is possible in their case. The physiological differences among plants determine the

selectivity. Systemic herbicide is also a term used to name a herbicide which is translocated.

Student’s Manual For Level One and Two in Agriculture 94

B. SOIL APPLICATIONS. Soil fumigants and soil sterilants fall into this group. They are

used where it is desired to remove all plant growth or to keep areas free from plant

growth.

(i)Soil fumigants. These materials are employed for killing all plant growth before

sowing more desirable species. They function as a vapour or as a gas that diffuses

through the soil and have a relatively short life in the soil ;as a result of which re-planting

in the treated area is possible within four weeks or less. Carbon disulphide, chloropicrin,

Vapam, Mehtylbromide and cyanamide are some soil fumigants in use.

(ii)Soil sterilants.These chemicals make the soil sterile for varying length of time

depending on the chemical used, the amount applied, rainfall,soil type ,organic matter

etc.The inorganic chemicals, borates and chlorates and the organic compounds.

C) AQUATIC APPLICATIONS. A number of chemicals is used for controlling

some submerged aquatic weeds by dissolving or emulsifying them in water in canals, ditches,

ponds and lakes. Some chemicals in use are aqualin, aromatic solvents, chlorinated benzenes,

copper sulphate, Endothal, Fenac and Sodium arsenite.

Formulation of herbicides.

Formulation refers to the way in which the basic weed killing chemicals are prepared for

practical use. Herbicides are formulated to be applied as solutions in water or oil, emulsions,

wettable powders, granules and dusts.

Solution of water or oils

The salt of most herbicides are soluble in water. They are dissolved in convenient amounts of

water and then sprayed.

The parent acid formulations of some of these are soluble in oil. They are often used to crease

the toxicity of soil sprays or to fortify the oil.

Emulsions.

An emulsion is one liquid dispersed in another liquid, each maintaining its original identity. The

two liquids are prevented from reacting with each other by the addition of an emulsifying agent.

Ester formulations of 2, 4-D are oil-like and form emulsions. Emulsions are milky.

Wettable powder

It is a type of formulation in which a herbicide is absorbed generally on an inert carrier, together

with an added surface acting agent, and finally ground so that it will form a suspension when

agitated with water.Simazine, Atrazine, Monuron, Diuron and Neburon are wettable powders.

Student’s Manual For Level One and Two in Agriculture 95

Granular herbicides

In these formulations the herbicides is adsorbed on, mixed with, or impregnated into, a generally

inert carrier in such a way that the final product consists of granular particles.

Many carriers are used, e.g. clay, sand vermiculate and finely ground plant parts. Granular

materials can be spread by hand or with mechanical spreaders. These materials have advantages

over sprays, because water is not needed for application, costlier spraying equipment is

dispensed with, and the granules fall off the leaves of valuable plants without causing injury.

Another advantage is that as the active weed-killing principle in these formulations is gradually

released, they suppress the growth of weeds for long.

Dusts.

Insecticides and fungicides are very often made in the form of dusts. However, only a few

herbicides are applied as dusts because of the drift hazard.

Student’s Manual For Level One and Two in Agriculture 96

Module 11

Weed Control

Weeds are wild plants that have deleterious effects on cultivated land and in gardens

Natural powers of Weed,

The ability of producing seeds abundantly

The ability to establish and spread themselves rapidly

The ability of the seeds to remain dormant for a long time

The ability of buried seeds to survive for a long time

The ability to adapt to various conditions in order to spread wider

Weeds have various negative effects. Mainly, by competing for space, nutrients in the soil, light, and

water, they impact crop yields negatively. Some of the other negative effects on agriculture are:

Insects use them as shelter for overwintering

They harbor crop diseases

They interfere with the harvest

They contaminate the produce, thus reducing their quality

They produce chemicals that are poisonous to humans, animals, and crop plants

Types of Weeds,

Various Types of Weeds

There are about 250,000 plant species around the world, and about 8000 species, or 3 percent, of them are

considered to be weeds. Here are some of the types of weeds that are commonly found in our gardens and

fields:

Ground Thistle (Cirsium acaulon): These grow hidden in grass and can remain undetected until they

Student’s Manual For Level One and Two in Agriculture 97

begin flowering. This is a perennial, with their spiny leaves forming a flat bed. The flowers are deep pink

in color and grow in the center of the cluster of leaves growing in a circular pattern.

Giant Foxtail (Setaria Faberi): This is a type of grass that grows erect. Its hairy ligule and the dense

hairs that grow on the surface of the upper leaves are what differentiates it from other grasses. It usually is

found amongst cultivated crops. It has an annual lifecycle.

Field Bindweed (Convolvulus arvensis): This weed has stems that are thin and wiry that twine around

anything close by. The flower is shaped like a trumpet and can be white or a light pink in color. Its

rootstock is woody, and it is very hard to get rid off. It has a perennial lifecycle.

Student’s Manual For Level One and Two in Agriculture 98

Stinging Nettle (Urtica dioica): This is of course quite a familiar weed, and gardening enthusiasts are

well aware how difficult it is to get rid of it. That is because it spreads via seed, roots, as well as stolons.

Its stem is woody and resists normal strimming. Its leaves are crinkled and deep green in color, with

strings of tiny flowers that are green in color. And of course it has nettles that sting, although it is

supposed to have herbal uses.

Ivy (Hedera helix): This is one of the most common creeper weeds that grows on walls as well as trees.

When it grows in the tree canopy, it often covers the branches, gradually killing the trees. When it grows

on the ground it displaces native plant species the leaves are usually heart-shaped and have 3-5 lobes. The

flowers are clustered and greenish-yellow in color. The young plants propagate rapidly, forming roots as

they grow, and are harder to remove once they get established.

Student’s Manual For Level One and Two in Agriculture 99

Dandelion (Taraxacum officinale): This weed is a problem in tilled fields, alfalfa fields, and in pastures.

Once the seedlings and plants get established they can interfere with the establishment of cultivated

species like legumes. The dandelion reproduces via seeds, and is a perennial plant. It is practically

stemless and the leves grow in a rosette, which are lobed and long, and have variable shapes. The flower

is bright yellow in color, which grow on a long stem, about 11-18 inches high. The seeds are attached to a

hairy parachute, which are carried by the wind.

Barnyard Grass (Echinochloa crus-galli): This is a type of annual grass that has flat, long leaves that

are usually purplish color at the base. While generally they grow upright, however some of them can be

spread out on the ground. The base of the stem is flattened. The seed heads are one of the distinctive

Student’s Manual For Level One and Two in Agriculture 100

features, usually purplish, with large sized seeds that look like millets which grow concentrated on

spikelets. These are regarded as one of the worst weeds, which cause crop yield reduction and the failure

of forage crops due to removing about 80 percent of the nitrogen in the soil. It also accumulates high

amounts of nitrates which can poison farm animals. It also harnors a number of viral diseases, and

mechanical harvesting can be hampered when they grow heavily.

Crop Weed Competition.

Reduction in crop yields due to weeds result from their multifarious ways of interfering with crop growth

and crop culture. Weeds compete with crops for one or more plant growth factors such as mineral

nutrients, water, solar energy and space and they hinder crop cultivation operations.

1. Competition for mineral nutrients: Being hardy and vigorous in growth habit; they soon outgrow

the crops and consume large amount of water and nutrients. Thus causing heavy losses in yields.

For e.g. Mani, found that on an average weeds growing in crop field during the kharif season

removed 46.6 kg/ha N, 12.1 kg/ha P and 73.3 kg/ha K.

In general, weeds removed N and K from soil in much greater quantity than P.

2. Competion for water: For producing equal amount of dry matter, the weeds, in general transpire

more water than most crop plants. It is reported that wild mustard transpires about four times

more water than a crop of oat.

Student’s Manual For Level One and Two in Agriculture 101

3. Competition for Solar Energy: About 99% of dry matter in plants is made up of organic matter

that is dependent on solar energy. When plants are mutually shaded, their production potential is

greatly reduced even though water and other nutrients are available to them in abundance.

4. Competition for space: Weeds compete for space both in the rhizosphere and atmosphere. In the

presence of weeds, crop plants also have limited space to develop their shoots, which amounts to

reduced photosynthesis in them.

5. Weeds reduce the crop quality: Weeds may reduce the quality of the crop produce in many ways.

Weed seed like wild mustard, sweet clover, a Mexican poppy and bullets of wild garlic and wild

onion when threshed and ground with winter grains can results in serious consequences besides

imparting objectionable odour to the flour. Khanna observed that striga (striga Spp.) reduced the

quality of sugarcane juice by 3.9 to 8.9 percent.

6. Weeds impair the quality of the animal produce: Many weeds in pastures and forage crops impart

undesirable flavours to milk and meat of animals. For e.g. Pivali tilwan (Cleome viscosa) imparts

undesirable flavour to milk. Gokharu or Landaga (Xanthium strumarium) get attached to the body

of sheep and seriously impair the quality of wool.

7. Weeds harm animal health: Several weeds of grasslands and forage crops contain high alkaloids,

tannis, oxalates, gulcosides, and other substances that prove poisonous to animals when ingested.

For e.g. Silky lupine ( Lupinus sericeus) is responsible for crooked calf disease.

8. Weeds harbour insect pests or diseases; Weeds either give shelter to various insect pests and

diseases or serve as alternate host. For e.g. Weed around paddy bunds harbour the gallfly.

9. Weeds damage human health: Health, comfort and work efficiency of man are also affected by

weeds directly or indirectly. For e.g. people in U.P. are plagued year after year with hay fever and

asthma aggravated by pollens of ragweed’s bursage. Tsetse fly which cause African sleeping

sickness.

10. Weeds contaminate water bodies: Aquatic weeds change the flavour appearance and taste of

drinking water. Aquatic weeds are a menace to fisheries too. Aquatic weeds on decomposition

gives offensive odours and pollute atmosphere.

11. Weeds cause quicker wear and tear to farm implements: Being hardy and deep-rooted, the tillage

implements get worn early.

12. Weeds reduce the value of the land: Agricultural lands heavily infested with perennial weeds like

Kans (Saccharum spontaneum) always fetch less price.

13. Less efficient use of land : In case of perennial weeds, the carrying capacity of the grazing lands

is reduced and cause depreciation of land value.

Student’s Manual For Level One and Two in Agriculture 102

14. Increase in cost of cultivation: In fields of crops infested with weeds, the tillage operations

require high cost.

15. Disturbance in Public places: it is desirable that public places be kept clean of weeds. Presence of

weeds around our living and working places makes the surroundings dull.

Plant Quarantine

Plant quarantine is vital to prevent the introduction of non-indigenous, potentially damaging pests and

diseases of plants into a country or to eradicate them before they can become widespread and well

established. Less-developed countries and other countries in transition are especially vulnerable to the

damaging effects of exotic pest introductions because of often inadequate infrastructure and the fragility

of their economies. The well-meaning importation of germplasm for agricultural development projects

creates a further risk of introducing such quarantine pests. Without stronger phytosanitary services nations

will be unable to participate in the liberalization of world markets. Our work involves natural and social

scientists from NRI and lawyers from the University's Law School

Pest risk analysis including monitoring, forecasting and project planning to avoid quarantine

problems;

Legislative support for developing phytosanitary procedures;

Project planning for germplasm importation and development;

Advice and assistance in design of inspection and treatment facilities;

Participation in global initiatives to replace ozone-layer damaging methyl bromide as fumigant

Development of diagnostic methods for detection of pathogens appropriate for use under a wide

range of conditions;

Development of integrated diagnostic systems for a wide range of plant pathogens;

Research and advice on control of storage pests and related aspects of post-harvest handling for

export and marketing of produce;

Training, education and institutional strengthening and support, including Master's level course Plant

quarantine and sustainable resource management

Hydroponics

THE WORD HYDROPONICS COMES FROM

A COMBINATION OF 2 GREEK WORDS

“Hydro” water

“Ponos” work

Student’s Manual For Level One and Two in Agriculture 103

By definition: Hydroponics means “water working”

Practical use: Growing plants without the use of soil.

IN HYDROPONIC PRODUCTION:

Plants get the exact nutrients

Nutrients are fed thru the roots

LESS STRESS

OPTIMUM PLANT GROWTH

• VIRTUALLY ANY PLANT WILL GROW IN HYDROPONICS

• SOME WILL DO BETTER THAN OTHERS

• IDEAL CROPS : TOMATOES, CUCUMBERS, PEPPERS, LEAFY

CROPS, HERBS AND FLOWERING PLANTS

Essential requirements for plant growth:

Temperature, Humidity, Light, Water, Air, Minerals & Support

Soil Not required BUT it provides

SOIL IS SIMPLY A HOLDER OF THE NUTRIENTS, A PLACE WHERE THE PLANT ROOTS

TRADITIONALLY LIVE AND A BASE OF SUPPORT FOR THE PLANT STRUCTURE

HOW DO SOIL PROVIDE THE PLANT ITS FOOD

In soil, biological decomposition breaks down organic

Matter into the basic nutrient salts that plants feed on. Water which is around the soil dissolves these

salts and allows uptake by the roots.

For a plant to receive a well balanced diet, everything in the soil must be in perfect balance. Rarely, if

ever, can you find such ideal conditions in soil due to contamination and biological imbalances.

Student’s Manual For Level One and Two in Agriculture 104

HOW IS FOOD PROVIDED - IN HYDRPONICS

With hydroponics, water is enriched with the very same nutrient salts that are in the soil, creating a

hydroponic nutrient solution that is perfectly balanced. And the plants have access to food all times.

And since this hydroponic nutrient solution is contained, it does not harm our environment as doe’s

runoff from fertilized soil.

ADVANTAGES OF HYDROPONICS

LESS WORK

FEW PESTS AND DISEASES

LESS WATER, FERTILIZER,

CHEMICALS ETC. LOW COST

HIGH PRODUCTION

ENVIRONMENTALLY FRIENDLY

CAN BE USED IN MANY ENVIRONMENTS, ANY TIME

HIGH NUTRITIONAL VALUE

METHODS OF HYDROPONIC PRODUCTION

AEROPONICS

Student’s Manual For Level One and Two in Agriculture 105

Aeroponics is an application of hydroponics without a growing medium, although a small amount

may be used to germinate the seed or root a cutting. Plant roots are suspended mid-air inside a

chamber kept at a 100% humidity level and fed with a fine spray of nutrient solution

This mid-air feeding allows the roots to absorb much needed oxygen, thereby increasing metabolism

and rate of growth reportedly up to 10 times of that in soil. And there is nearly no water loss due to

evaporation

THINGS YOU NEED TO KNOW------ NUTRIENTS

Plants need 16 nutrients for optimal

MACRONUTRIENTS: Nitrogen, potassium, phosphorus, sulphur, calcium, and magnesium

DOMINANT FUNCTIONS:

Nitrogen -- promotes development of new leaves

Phosphorus -- aids in root growth and blooming

Potassium -- important for disease resistance and aids, growth in unfavorable temperatures

Sulfur -- contributes to healthy, dark green color in leaves

Calcium -- promotes new root and shoot growth

Mg -- chlorophyll, the pigment that gives plants their green color and absorbs sunlight to make

food.

PLANTS NEED 16 NUTRIENTS FOR OPTIMAL GROWTH

MICRONUTRIENTS: BORON, COPPER, COBALT, IRON, MANGANESE, MOLYBDENUM &

ZINC

FUNCTION: Constituents of Enzyme

- Nitrogen Fixation

- Respiration

- Carbohydrate Breakdown Etc.

Student’s Manual For Level One and Two in Agriculture 106

ALL NUTRIENTS PACKED: FERTIZER

Fertilizer Dissolved In Water

Nutrient solution

THINGS NEED TO KNOW------ pH

The pH of a nutrient solution is a measurement of its

Relative concentration of positive hydrogen ions

Plants feed by an exchange of ions. As ions are removed from the nutrient solution, pH rises.

The more ions that are taken up by the plants, the greater the growth.

When the pH is below 7.0, there are more hydrogen ions than hydroxyl ion. Such a solution

"acidic."

When the pH is above 7.0, there are fewer hydrogen ions than hydroxyl ions. This means that

the solution is “alkaline. “

pH REQUIREMENT DIFFERS FOR DIFFERENT PLANTS

Ranges from 5.5-6.5 for optimum growth

THINGS NEED TO KNOW------EC

Electrical Conductivity: Strength of Nutrient Solution

As salts are dissolved into the pure water, electricity begins to be conducted.

The more salts that are dissolved, the stronger the salt solution and, correspondingly, the more

electrical current that will flow.

Measure by a Meter Call EC meter

Different plants require different EC

Student’s Manual For Level One and Two in Agriculture 107

Module 12.1

Identification of Weeds

Common Name Scientific Name Weed Type Life Cycle

Bermudagrass

Cynodon dactylon Grass Summer perennial

Bittercress, Hairy

Cardamine hirsute Broadleaf Winter annual

Bluegrass, Annual

Poa annua Grass Winter annual

Buttercup, Small Floweed

Ranunculus Broadleaf Winter Annual

Carpetweed

Mollugo verticillata Broadleaf Summer annual

Student’s Manual For Level One and Two in Agriculture 108

Chamberbitter

Phyllanthus urinararia Broadleaf Summer Annual

Chickweed, Common

Stellaria media

Broadleaf

Winter annual

Clover, White

Trifolium repens Broadleaf Winter perennial

Crabgrass

Digitaria sp. Grass Summer annual

Cudweed, Purple

Gnaphalium purpureum Broadleaf Winter annual

Dandelion

Taraxacum

officinale Broadleaf Winter perennial

Student’s Manual For Level One and Two in Agriculture 109

Eclipta

Eclipta prostrata Broadleaf Summer annual

Field Madder

Sherardia arvensis Broadleaf Winter annual

Garlic, Wild

Allium vineale

Monocot

Winter perennial

Geranium, Carolina

Geranium carolinianum Broadleaf Winter annual

Goosegrass

Eleusine indica Grass

Summer annual

Henbit

Lamium amplexicaule Broadleaf Winter annual

Student’s Manual For Level One and Two in Agriculture 110

Marestail

Conyza canadensis Broadleaf Summer annual

Mulberry Weed

Fatoua villosa Broadleaf Summer annual

Nutsedge, Purple

Cyperus rotundus Monocot Summer perennial

Nutsedge, Yellow

Cyperus esculentus

Monocot Summer perennial

Pigweed, Smooth or

Common

Amaranthus hybridus Broadleaf Summer annual

Student’s Manual For Level One and Two in Agriculture 111

Primrose, Cutleaf Evening

Oenothera laciniata Broadleaf Winter annual

Sedges, Annual/Rice

Flatsedge

Cyperus sp. Monocot Summer annual

Shepherd's Purse

Capsella bursa-pastoris Broadleaf Winter annual

Sorrel, Red

Rumex acetosella Broadleaf Summer perennial

Sorrel, Wood

Oxalis europaea Broadleaf Summer perennial

Student’s Manual For Level One and Two in Agriculture 112

Speedwell, Corn

Veronica arvensis

Broadleaf

Winter annual

Spurge, Spotted

Chamaesyce maculata Broadleaf Summer annual

Spurge, Prostrate

Chamaesyce humistrata Broadleaf Summer annual

Virginia Pepperweed

Lepidium virginicum Broadleaf Summer annual

Preventive measures of weed growth

In order to reduce weed growth, many weed control strategies have been developed. The most basic is

tillage, which cuts the roots of annual weeds. Today, chemical weed killers known as herbicides are

widely used.

In small scale farming, methods of weed control include, mechanical control such as hand weeding and

weeding with a hoe mulching, and in other countries application of herbicides.

Weeds should be removed before they produce seeds, so that new weed plants will not emerge. If weeds

with ripe seeds are left on the land there will be more weed growth in the following season. On fallow

Student’s Manual For Level One and Two in Agriculture 113

fields, slash the weeds just before they set seeds. These slashed weeds provide excellent mulch and break

down to enrich the soil with organic matter. The slashed weeds could also be used for mulch elsewhere.

Use of Organic Pest Control

Avoiding chemical pesticides in your home lawn and garden is a great step to ensuring

the health and safety of your family, pets, neighborhood, and the earth!

Exposure to pesticides has been linked to a long list of diseases and health problems: Parkinson’s,

infertility, cancer, birth defects, encephalitis, and lymphoma, just to name a few.

Beauveria Bassiana

Another biological pesticide, Beauveria bassiana, is a fungus that infects aphids, caterpillars,

grasshoppers, ants and other insects and multiplies until it kills its host. The organic farming book,

"Resource Guide for Organic Insect and Disease Management," reports that this fungus occurs naturally

in some soils but is cultivated specifically as an organic pesticide.

Kaolin Clay

Kaolin clay is a type of clay that, according to the U.S.EPA, was approved as an organic pesticide in

1998. It is used on various types of produce to protect against mites, insects, fungi, and harmful bacteria.

It is sprayed on plants or trees in a powdered form to act as a physical barrier between pests and the

plants.

Neem Oil

Neem oil is brown oil with an unpleasant taste and smell that acts as a repellent for insects and is non-

toxic to humans and beneficial insects such as honey bees. The U.S. EPA reports that neem oil is pressed

from the seeds of the neem tree, which is native to India.

Pyrethrum

Although pyrethrum is a natural botanical pesticide that comes from dried flowers, not all forms of this

pesticide are approved for organic use because of the levels of toxicity it can contain, states the "Resource

Guide for Organic Insect and Disease Management." Mixtures of pyrethrum that have been approved for

use in organic farming will be labeled as such.

Plant Oils

There are several different types of plant oils that are used as organic pesticides. The U.S. EPA lists

orange oil, canola oil, mustard oil, castor oil and soybean oil among them. They are used to either kill or

Student’s Manual For Level One and Two in Agriculture 114

repel insects and are also used to repel larger pests, such as cats, dogs or deer. Of all the plant oils

approved for use as organic pesticides, only wintergreen oil is noted for having a toxic effect on humans

in high doses.

Inorganic pesticides like borates, silicates and sulfur, are minerals that are mined from the earth and

ground into a fine powder. Some work as poisons and some work by physically interfering with the pest.

Older "inorganics" included such highly toxic compounds as arsenic, copper, lead and tin salts. Current

inorganic pesticides are relatively low in toxicity and have low environmental impact. Borate insecticides,

for example Bora Care and Timbor, in particular, have many uses in structural pest management

Weed Prevention:

Use of Mulch

"Hot" Composting

Soil Solarization

Weed Control:

Hand Weeding

Use of Flame or Heat

Use of Biological Control Agents

Student’s Manual For Level One and Two in Agriculture 115

Module 12.2

Pest management

Fungi

Fungi are a diverse group of organisms with close ties to agriculture. Some fungi create devastating

diseases in crops, while others are crops themselves (mushrooms). Other fungi are used successfully to

protect crops from a variety of pests. Among the most prominent of these are the fungi that are used

against insects and other related pests.

Most fungi used for the control of insect pests belong to the group hyphomycetes. Some species have

been developed as commercial products because of their ability to be mass produced. Most fungi in this

group are usually found in the soil and can cause natural outbreaks on their own when environmental

conditions are favorable. They can infect a wide range of insect hosts. Specific fungal strains in

commercial products target thrips, whiteflies, aphids, caterpillars, weevils, grasshoppers, ants, Colorado

potato beetle, and mealybugs. Currently (2008) allowable products containing the hyphomycete

fungus, Beauveria bassiana that are commercially available include Mycotrol O (Emerald

BioAgriculture), Naturalis Home and Garden (H&G) and Naturalis L (Troy BioSciences, Inc.). Before

applying any pest control product, make sure to include what you might want to use and how you intend

to use it in your organic system plan and get your certifier's approval)

There is another commonly encountered group of fungi called the entomophthorales. Fungi in this group

can cause natural outbreaks in the populations of their insect hosts, but they are difficult to mass produce

and as yet are not in commercial production. They tend to be much more host specific; one well known

species only infects aphids. Despite the difficulties in producing them commercially, they can still have a

large impact on the pest populations they infect. There are currently no commercially-based products

available for organic vegetable production.

Life cycle of fungi infecting insects

Fungi that infect insects are found in the environment as spores. Insects can become infected when they

come into contact with spores on the surface of plants, in the soil, in the air as windborne particles, or on

the bodies of already dead insects (Figure 1). Spores attach to the surface of the insect and infect by

penetrating through the insect cuticle, often at joints or creases where the insect’s protective covering is

thinner. Once inside, the fungus grows throughout the body of the insect. Many fungi also produce toxins

in the host that increase the speed of kill or prevent competition from other microbes.

Student’s Manual For Level One and Two in Agriculture 116

Figure 1. Generalized life cycle of fungi infecting insects (spores not to scale). Figure credit: Jim McNeil,

Department of Entomology, Penn State University.

Usually after the insect has died, the fungus grows out through the outer covering (exoskeleton) of the

insect, usually at thinner areas like joints or creases, and begins to produce spores. The spores of

commercially developed fungi in the group hyphomycetes are spread passively by the action of the wind,

rain, or contact with other hosts or animals in the environment. The spores of fungi that create natural

outbreaks, in the group entomophthorales, are often actively ejected from the dead insect. Since many

species in this group of fungi infect insects which cluster together, like aphids, this tactic can drastically

increase the spread of the infection. Insects killed by fungi often have a “fuzzy” appearance, caused by

the growth of the fungus out of the exoskeleton to produce spores. Most commercial strains of fungi

produce spores that are either white or green in color, although the color of the fungi can change over

time as the fungus grows and ages.

Spores that do not encounter a host either die or persist in sheltered areas of crop plants or in the soil.

Although some species of fungi can produce spores which can persist for years in the soil, most spores are

only viable for a growing season or a year at most.

Advantages and disadvantages of fungi for controlling insect pests

Advantages

Fungi make good biological control agents for a variety of reasons. They generally do not affect people or

other mammals, making them extremely safe to use. It is relatively easy to mass produce spores of insect-

parasitic fungi in the hyphomycete group, so they are comparably priced with other biological control

agents, such as bacteria. Most commercial fungal products are formulated as spores, which are easily

Student’s Manual For Level One and Two in Agriculture 117

adapted to existing application technology, such as spray rigs. The relatively broad host range of many

fungi means one can often achieve control of multiple pests with the same product. Finally, successful

infections can spread to other hosts and lead to high rates of persistence within a growing season, even if

between season persistence tends to be low for most types of fungi.

Disadvantages

High concentrations of spores are often needed to get adequate control of pests in a crop, which can cut

down on the cost effectiveness of fungal products. The kill time is relatively long (~1 week for most

fungi), although strains used for commercial products are chosen to kill as fast as possible. Their broad

host range can sometimes be a problem, especially if beneficial insects (i.e. predators, parasitoids, and

pollinators) are present in a crop; non-target mortality in these populations of beneficial insects can

negatively impact the success of the overall biological control program. Environmental factors can also

play an important role in the success of fungi. Moist conditions or high relative humidity in the canopy of

the crop are often necessary for control to be effective. Prolonged exposure to sunlight can also inactivate

spores, reducing persistence in the crop. Owing to these environmental limitations, natural outbreaks of

fungi tend to be sporadic and very patchy in the environment, which can limit their effectiveness in

controlling pests.

Virus

As more greenhouse crops are produced by vegetative cuttings, greenhouse growers are more concerned

about the potential of viruses to infect their crops. Some of the viruses that may infect greenhouse crops

include (but are not limited to): calibrachoa mottle virus, cucumber mosaic virus, tobacco mosaic virus,

tobacco ring spot virus, tomato ringspot viruses and tospoviruses including impatiens necrotic spot virus

and tomato spotted wilt virus.

There is no control for plants infected with a virus. It is important to have the virus disease accurately

identified. Serological techniques such as ELISA (enzyme-linked immunosorbent assay) are now

available to accurately identify a wide range of viruses. On-site grower kits using this same technology

are also available to test for viruses such as calibrachoa mottle virus, cucumber mosaic virus, impatiens

necrotic spot virus and tobacco mosaic virus as well as others.

Symptoms

Virus symptoms can be easily confused with nutritional disorders, chemical spray injury, fungal or

bacterial pathogens or injury from fumes from a faulty furnace.

Symptoms can also vary depending with the type of virus, the host plant, how long the host plant has been

infected, the strain of the virus, and the environmental conditions. Symptom expression can be

temperature sensitive – some viruses are expressed at high temperatures whereas others are expressed at

lower temperatures. Viral symptoms can also be masked when the plants are growing vigorously.

Sometimes, symptoms may only be apparent when multiple infections are present or when plants become

stressed. So, don't rely on visual diagnosis to determine whether or what type of virus is present. You may

not become aware of a problem until it is widespread. Routine testing of plants showing symptoms and

those not showing symptoms is needed, especially before taking cuttings.

Student’s Manual For Level One and Two in Agriculture 118

Viruses rarely kill their hosts but they alter the host plants appearance. Some virus-infected plants are

propagated because of their attractive appearance! As an example, the variegated foliage in flowering

maple is due to the abutilon mosaic virus.

Mosaic (a variable pattern of chlorotic and healthy tissue on the same leaf), distortion of leaves or

flowers, yellow or chlorotic streaking, yellow veins, ring spots, dead brown areas (necrosis), and unusual

line patterns may be symptoms of viral infections. Stunting is common. Infected plants may also show

only mild symptoms or symptoms may be latent. For example, cultivated geraniums infected with

pelargonium flower break virus usually show no symptoms.

Causal Agents and Disease Development

Viruses are ultra-microscopic particles that infect living cells and alter their host's development. They

consist of nucleic acids surrounded by a protein coat. Viruses usually begin infection through a wound,

often from insect feeding. Once a plant is infected, the virus spreads systemically within the plant.

Plant viruses are often named on the basis of the symptoms they cause on the host first detected. For

example, a virus causing light and dark green areas (mosaic patterns) that was first seen on tobacco was

named tobacco mosaic virus.

Viruses can be transmitted by insects, primarily aphids; leafhoppers, and thrips sometimes, whiteflies can

transmit viruses. Mites, fungi and nematodes can occasionally transmit viruses. Viruses are often spread

by the propagation of infected plant parts (cuttings, bulbs, and sometimes seeds) and some can also be

spread by mechanical means including contact (rubbing, abrasion, or by handling).

Many different weeds can also become infected with viruses without showing symptoms. Weed control is

so critical because the weeds can be both reservoirs of a virus plus an alternative host of the insect vector.

Calibrachoa Mottle Virus (CbMV)

Calibrachoa Mottle Virus has been recently identified in calibrachoa. Infected plants may show streaking

in the flowers, interveinal chlorosis and mottling or blotching on the leaves. Some cultivars will not show

symptoms unless they are stressed. Calibrachoa mottle virus is transmitted mechanically in plant sap.

Currently, researchers are investigating if a vector plays a role in its spread.

Cucumber mosaic virus (CMV)

Cucumber mosaic virus has a wide host range of over 400 species of plants. CMV has been reported on

ajuga, aquilegia, campanula, delphinium, dahlia, lilium, petunia and phlox. Infected plants may show mild

mosaic patterns and mottling, flower color breaking, flecking, and fern leaf distortion.

CMV is primarily spread by aphids that can acquire the virus in as little as 5 to 10 seconds. Aphids then

move the virus from plant to plant for a few hours. CMV is also spread mechanically in the plant sap

when cuttings are taken from infected stock plants. CMV is also both seed and pollen transmitted in

petunia where symptoms develop in very young plants.

Rogue diseased plants. Control aphids. Eliminate weeds such as common pokeweed, chickweed, field

bindweed, yellow rocket, and bittersweet nightshade that may be reservoirs of CMV.

Student’s Manual For Level One and Two in Agriculture 119

Tobacco mosaic virus (TMV)

Tobacco mosaic virus has a wide host range but is especially a

concern on solanaceous crops. In recent years, TMV has been

reported on ajuga, calibrachoa, cyclamen, epimedium, gerbera,

helianthus, impatiens, lisianthus, lysimachia, New Guinea impatiens,

nicotiana, pepper, petunia, penstemon, tomato and torenia.

Symptoms include yellow mottling, upward leaf curling and overall

stunting. Some infected plants may not show any symptoms at all.

Different strains of TMV exist, too. A specific strain known as

odontoglossum ringspot virus (TMV-O) causes ringspots or line patterns on orchids.

TMV is not transmitted by insects! TMV is a very stable

virus that can be spread by contact. Workers can easily

spread this virus when they handle plants or when cutting

tools become contaminated. TMV can persist in dried

tobacco leaves, so tobacco products can also be a source of

TMV.

Discard infected plants including roots. Disinfect hands by

washing with milk, or tri-sodium phosphate and then thoroughly with soap and water. Smokers need to

wash their hands before entering the greenhouse so they do not infect plants. In greenhouses, hard

surfaces such asdoorknobs, or flats can become contaminated after handling virus-infected plants and

remain a source of infection. Thoroughly disinfect the growing area with a commercial disinfectant.

See references for more information. Control perennial weeds in the solanaceous family such as ground

cherry and horsenettle that could be reservoirs of TMV.

Tobacco ringspot virus (TRSV)

Tobacco ringspot virus has a narrow host range. It has been reported on begonia, geranium, impatiens,

iris, phlox, petunia, portulaca, and verbena. Ringspots are the primarily symptom. Tobacco ringspot virus

is spread mechanically, by nematodes (Xiphinema) and by seed in petunia. It is not spread by contact.

Tomato ringspot virus (ToRSV)

Tomato ringspot virus also has a narrow host range, and has been reported on begonia, chrysanthemum,

geranium, impatiens and orchids. Ringspots are the primary symptom. It can be transmitted mechanically,

by nematodes (Xiphinema), in the seed or pollen.

Tospoviruses

Tospoviruses including impatiens necrotic spot virus (INSV)

and tomato spotted wilt virus (TSWV) have a very wide host

range of over 600 hosts. It has been reported on begonia,

campanula, centranthus, cyclamen, garden impatiens, monarda,

New Guinea impatiens, pepper, phlox, primula, tomato and

many others. Infected plants may show stunting, necrotic and

chlorotic spotting, stem cankers, line patterns and ringspots.

Tospoviruses are spread by thrips. Thrips cannot transmit the

virus unless they acquire it as first instar larvae when they feed

Student’s Manual For Level One and Two in Agriculture 120

upon infected plants (including weeds). Winged adults are primarily responsible for viral spread.

Tospoviruses are also spread in the sap when cuttings are taken from infected plants.

Rogue infected plants. Use yellow or blue sticky cards to monitor for thrips and promptly begin a strict

thrips management program. When tospoviruses are present, the threshold level for thrips is zero.

Prevention The best way to control viruses are to keep them out of production areas. Prevention is the grower's first

line of defense against virus infection.

Purchase clean, virus-free seed, cuttings and stock plants from a reputable supplier. Virus-indexed plant

material may be available for certain crops. If unsure, isolate incoming plants in quarantine type area until

you have determined that they are virus-free.

Do not take cuttings from infected stock plants. Many viruses are spread mechanically in the sap that

contaminates worker's hands or cutting tools. To remove contamination of most viruses from tools, they

can be soaked in quaternary ammonium compounds or hydrogen dioxide. Soak the tools for at least one

minute. Propagators need to soak their cutting tools on a regular basis, after use on each stock plant or

defined area.

Control insect vectors. If designed and maintained properly,

the use of insect screening in propagation areas can help to

reduce insect pressure.

Keep growing areas weed-free. Weeds can be reservoirs

both of viruses and their insect vectors. Discard virus

infected plants.

Bacterial pests

Several bacterial pathogens that have been used as insecticides include (a) endospore forming Bacillus

and Clostridium species (b) non-endospore forming species of Pseudomonas, Enterobacter, Proteus,

Serratia, Xenorhabdus. Of the potential bacterial pesticides, Bacillus thuringiensis has been most

extensively studied.

Bacillus thuringiensis has been successfully tested against more than 140 insect species (Lepidoptera,

Hymenoptera, Diptera and Coleoptera). At present, there are 12 groups of B. thuringiensis. All strains

produce protein crystal inclusion bodies which act as endotoxin. They are toxic factors and are called

parasporal bodies.

These crystals dissolve under alkaline condition. They are not soluble in water under neutral or acidic

condition. The midgut contents of the caterpillar larvae (pests) are alkaline. On ingestion, the crystal

dissolves in the midgut fluid and gets digested particularly by the proteolytic enzyme present in the

midgut fluid. This digested protein crystal attacks the cementing substances which are present in the gut

wall, thus loosening the epithelial gut wall which helps continuous diffusion of liquid from the gut into

the blood making the blood of the insect highly alkaline and leading to gut paralysis. The parasporal

bodies are highly toxic for caterpillars with an LD50 value of < 0.9 mg/ g of larvae.

Student’s Manual For Level One and Two in Agriculture 121

The process of crystal synthesis and spore formation proceeds simultaneously. The toxin production by a

culture can be enhanced by controlling many factors Bacillus thuringiensis toxin genes have been

introduced via recombinant DNA technology into the genome of plants or plant associated

microorganisms.

Student’s Manual For Level One and Two in Agriculture 122

Module 12.3

Pesticides

A pesticide is a substance, mixture or organism made or used for destroying any pest.

As well as insects, a pesticide may be used for eliminating weeds or moulds, preserving woods and

regulating plant growth.

A pesticide is designed to destroy organisms that you don't, and avoid harming those that you do want. So

a weed killer will selectively kill unwanted plants whilst leaving the crop unharmed.

Risks of pesticides

When a pesticide comes into contact with a surface or an organism, that contact is called a pesticide

exposure. For humans, a pesticide exposure means getting pesticides in or on the body. The toxic effect of

a pesticide exposure depends on how much pesticide is involved and how long it remains there.

Types of Exposures

Pesticides contact your body in four main ways:

oral exposure (when you swallow a pesticide),

inhalation exposure (when you inhale a pesticide),

ocular exposure (when you get a pesticide in your eyes), or

dermal exposure (when you get a pesticide on your skin).

Avoiding Exposure

Avoiding and reducing exposures to pesticides will reduce the harmful effects from pesticides. You can

avoid exposures by wearing appropriate personal protective equipment, washing exposed areas often, and

keeping your personal protective equipment clean and in good operating condition.

Causes of Exposure

One of the best ways to avoid pesticide exposures is to avoid situations and practices where exposures

commonly occur.

Student’s Manual For Level One and Two in Agriculture 123

Oral exposures often are caused by:

not washing hands before eating, drinking, smoking, or chewing,

mistaking the pesticide for food or drink,

accidentally applying pesticides to food, or

splashing pesticide into the mouth through carelessness or accident.

Inhalation exposures often are caused by:

prolonged contact with pesticides in closed or poorly ventilated spaces,

breathing vapors from fumigants and other toxic pesticides,

breathing vapors, dust, or mist while handling pesticides without appropriate protective

equipment,

inhaling vapors present immediately after a pesticide is applied; for example, from drift or from

reentering the area too soon, and

using a respirator that fits poorly or using an old or inadequate filter, cartridge, or canister.

Dermal exposures often are caused by:

not washing hands after handling pesticides or their containers,

splashing or spraying pesticides on unprotected skin or eyes,

wearing pesticide-contaminated clothing (including boots and gloves),

applying pesticides in windy weather,

wearing inadequate personal protective equipment while handling pesticides, and

Touching pesticide-treated surfaces.

Eye exposures often are caused by:

splashing or spraying pesticides in eyes,

applying pesticides in windy weather without eye protection,

rubbing eyes or forehead with contaminated gloves or hands, and

Pouring dust, granule, or powder formulations without eye protection.

Harmful Effects

Pesticides can cause three types of harmful effects: acute effects, delayed effects, and allergic effects.

Student’s Manual For Level One and Two in Agriculture 124

Acute Effects

Acute effects are illnesses or injuries that may appear immediately after exposure to a pesticide (usually

within 24 hours). Acute effects usually are obvious and often are reversible if appropriate medical care is

given promptly.

Pesticides cause four types of acute effects:

acute oral effects,

acute inhalation effects,

acute dermal effects,

acute eye effects.

Acute oral effects -- Your mouth, throat, and stomach can be burned severely by some pesticides. Other

pesticides that you swallow will not burn your digestive system, but will be absorbed and carried in your

blood throughout your body and may cause you harm in various ways.

Acute inhalation effects -- Your entire respiratory system can be burned by some pesticides, making it

difficult to breathe. Other pesticides that you inhale may not harm your respiratory system, but are carried

quickly in your blood throughout your whole body where they can harm you in various ways.

Acute dermal effects -- Contact with some pesticides will harm your skin. These pesticides may cause

your skin to itch, blister, crack, or change color. Other pesticides can pass through your skin and eyes and

get into your body.

Acute eye effects -- Some pesticides that get into your eyes can cause temporary or permanent blindness

or severe irritation. Other pesticides may not irritate your eyes, but pass through your eyes and into your

body.

Delayed Effects

Delayed effects are illnesses or injuries that do not appear immediately (within 24 hours) after exposure to

a pesticide or combination of pesticides.

Allergic Effects

Allergic effects are harmful effects that some people develop in reaction to substances that do not cause

the same reaction in most other people.

Student’s Manual For Level One and Two in Agriculture 125

Types of allergic effects -- Some people are sensitized to certain pesticides. After being exposed once or a

few times without effect, they develop a severe allergy-like response upon later exposures.

These allergic effects include:

systemic effects, such as asthma or even life-threatening shock,

skin irritation, such as rash, blisters, or open sores, and

eye and nose irritation, such as itchy, watery eyes and sneezing.

Signs and Symptoms of Harmful Effects

Watch for two kinds of clues to pesticide-related illness or injury. Some clues are feelings that only the

person who has been poisoned can notice, such as nausea or headache. These are symptoms. Others

clues, like vomiting or fainting, can be noticed by someone else. These are signs.

Many of the signs and symptoms of pesticide poisoning are similar to signs and symptoms of other

illnesses you might experience, such as the flu or even a hangover. Examples of signs of pesticide-related

illness or injury include:

External irritants cause:

redness, blisters, rash, and/or burns on skin, and

swelling, a stinging sensation, and/or burns in eyes, nose, mouth, and throat.

Pesticide poisoning may cause:

excessive sweating, chills, and/or thirst,

chest pains,

difficult breathing,

cramps in your muscles or aches all over your body.

Spraying of pesticides

When applying pesticides, you are not generally exposed to the same high concentration of pesticide as

during the mixing and loading operation. However, the time-length of exposure is much longer, thus the

cumulative exposure may be equal to or greater than during the mixing-loading operation.

Student’s Manual For Level One and Two in Agriculture 126

Pesticide applications are made with everything from hand sprayers and dusters, to irrigation equipment

and aircraft. Whatever equipment is used, many of the safety precautions are the same. These include:

1. Read and follow the label. Applications made which vary from label requirements are a violation

of federal law.

2. Use the correct equipment, and make sure it is properly maintained and adjusted. Screens,

strainers and nozzles should be clean and functioning properly. Nozzles should be of the right

type and properly adjusted and all lines, valves, seals should be checked for leaks.

3. The application equipment should be accurately calibrated on a regular basis. Whenever you have

any suspicion that the equipment is applying an inaccurate amount, recalibrate it. Information on

calibration is provided within this guide.

4. Wear the proper protective clothing and equipment.

5. Check the weather forecast frequently to determine if conditions will be favorable for the

application and effectiveness of the pesticide. The National Weather Service provides a

continuously updated weather forecast.

6. Avoid spraying near sensitive areas where drift could damage neighboring crops or the

environment. When spraying must be done in these areas, attempt to spray when the air is still,

humidity is high and any potential drift will be away from sensitive areas.

7. Lower pressures, proper boom and nozzle adjustments, larger nozzle size and drift reducing

additives (if the label permits) will reduce drift.

8. Do not make field adjustments to the sprayer in a recently sprayed, still-wet area. Move to an

unsprayed area.

9. Never attempt to clean a nozzle, screen or hose by blowing or sucking on it with your mouth. Use

small soft-bristle brushes and/or an air pressure bulb for these purposes.

10. Always empty a tank by spraying the entire contents onto the vegetation or other area for which

it was intended. Never drain a spray tank onto the ground. Important: Never mix more than you

need!

Storage and Handling of pesticides

Follow all storage instructions on the pesticide label.

Store pesticides high enough so that they are out of reach of children and pets. If possible, keep

all pesticides in a locked cabinet in a well-ventilated utility area or garden shed.

Never store pesticides in cabinets with or near food, animal feed, or medical supplies.

Student’s Manual For Level One and Two in Agriculture 127

Store flammable liquids outside your living area and far away from an ignition source such as a

furnace, a car, an outdoor grill, or a power lawn power.

Always store pesticides in their original containers, which includes the label listing ingredients,

directions for use, and first aid steps in case of accidental poisoning.

Never transfer pesticides to soft drink bottles or other containers. Children or others may mistake

them for something to eat or drink.

Use child-resistant packaging correctly - close the container tightly after using the product. Child

resistant does not mean child proof, so you still must be extra careful to store properly - out of

children's reach - those products that are sold in child-resistant packaging.

Do not store pesticides in places where flooding is possible or in places where they might spill or

leak into wells, drains, ground water, or surface water.

Transporting Pesticides

Bag pesticides separate from groceries

crash together.

Secure containers upright to make sure containers cannot fall or be knocked over.

Transport in trunk of car, away from people and groceries.

Student’s Manual For Level One and Two in Agriculture 128

Module 12.4

USING METHODS OF PESTICIDES Choice of Pesticide and Application Methods

Pest Identification and Population

Identify the pest accurately then refer to product manuals, advisors, or literature to identify the product or

products that will do the job. When scouting pests, it is also important to accurately assess population

levels.

If pest populations are below economic threshold levels there may be no

reason to spray at all.

Identification and Population of Beneficial Organisms

It is also a good idea to assess the kinds of numbers of beneficial organisms in the field. If their numbers

are high they may be able to control the pest without spraying. Additionally, spraying may do more

damage to the beneficials resulting in a more serious pest problem than would have occurred without

spraying. If beneficials are present and spraying is indicated, you should choose a pesticide that has the

least

effect on beneficials.

Level of Infestation/Stage of Crop Development

Assess the number of pests or immature stages such as eggs, larvae and whether the observed level poses

an immediate threat. Government department (Ministry of Agriculture or Health) often set "thresholds"

above

which it is necessary to control pests. It is, however, important to relate the infestation to the stage of crop

development.

After establishing the nature and level of the infestation and having identified a range of products that will

bring it under control, it is necessary to select the most appropriate product. The following criteria should

be applied:

Student’s Manual For Level One and Two in Agriculture 129

Selectivity

High selectivity is not very common but if possible, choose the pesticide that will cause the least damage

to non-target species.

Mammalian Toxicity

Products that are of low toxicity to man and other mammals are preferable to those which pose significant

hazard.

Method of Application

Match the product to the available equipment for application. Certain formulations cannot be used with

knapsack or other hydraulic sprayers.

Persistence

Check the product label for information about the persistence or length of activity. In certain

circumstances, it is useful to have a product which will remain active for several days or even weeks. If

an infestation occurs shortly before harvest, choose a product that will not leave residues which may be

harmful to consumers. Check for the pre-harvest interval in the product labels.

Mode of Action

Bear in mind that products work in different ways. Knowledge of pests and how a certain product works

can help you maximise the effectiveness of the product.

Avoidance of Resistance

With chronic infestations, i.e. those which may continue throughout the season and which may need

several applications for even partial control, do not spray repeatedly with the same product or family of

products. For example, early in the season use a relatively selective product to minimize damage to

predators and other beneficial insects. Later in the season choose a broad spectrum if necessary.

Student’s Manual For Level One and Two in Agriculture 130

Application Method and Choice of Equipment

Insecticides and fungicides are usually applied as foliar sprays, and herbicides are mostly sprayed

either onto the foliage or the soil. Thus spraying of liquid and wettable powder formulations is the most

common method of application and consequently a wide variety of hand-operated and powerdriven

spray apparatus has been developed over the years. Other formulations such as granules, dusts and

fumigants require different equipment for their application or none at all. For example, granules can

either be applied by mechanical spreaders or broadcast by hand. In Asian countries, most pesticides are

applied with small, handoperated, hydraulic sprayers or hand-held spinning disc sprayers.

Depending on the type of agricultural practices and economic development of the area, mist-blowers and

power-operated hydraulic or rotary cage sprayers mounted on tractor or aircraft may also be used

extensively.

Hand-Operated Sprayers

There are various types of hand-operated sprayers, but they can be broadly categorised into two groups:

1. Sprayers with hydraulic nozzles designed with systems to generate pressure at the nozzle to achieve

correct atomisation. With lever-operated sprayers the main tank is not pressurised, but spray pressure is

generated in a pressure chamber by constant pumping. With compression sprayers, the whole

tank is pressurised prior to spraying.

LEVER-OPERATED KNAPSACK SPRAYERS

• DIAPHRAGM PUMP KNAPSACK SPRAYERS

A. UPSTROKE B. DOWNSTROKE

Student’s Manual For Level One and Two in Agriculture 131

A. Upstroke B.Downstroke

COMPRESSION SPRAYERS

Student’s Manual For Level One and Two in Agriculture 132

2. Rotary atomisers, which generate spray droplets from a spinning disc or cup. These types typically

apply low volumes of spray liquid per hectare. These low volumes mean that higher concentrations of

spray liquid are applied; this makes them unsuitable for some products. In particular they should never be

used for paraquat application as the concentrations are likely to exceed recommended dilution rates.

1. Sprayer with centrifugal-energy nozzles

2. Electrostatic spraying equipment

3. Rope-wick herbicide applicators

Nozzles

The nozzle is one of the most important parts of the sprayer, since it is doing the job of producing the

spray droplets. Adjustable nozzles are commonly supplied with knapsack sprayers but these should never

be used for pesticide application as they do not allow safe calibration. It is quite easy to change their rates

and patterns and spray operators tend to accidentally and randomly adjust them during spraying.

Calibrating Hand-Operated Knapsack Sprayer

Accurate calibration of the sprayer is an important part of every spraying operation to ensure that the

pesticide is applied at the rate specified on the product label. Failure to calibrate has 3 major

consequences:

Too much chemical is applied. This is wasteful and expensive and can lead to environmental

problems or crop residues being unacceptably high.

and perhaps may require re-treatment which is again costly and time-wasting. Under-dosing may

also lead to rapid development of pest resistance.

Considerable amounts of unused spray liquid left over after the spray operation. Disposal of left

over spray liquid is difficult and time consuming and poses risks to the person disposing, to other

humans and to the environment.

Calibration Procedure

The aim of calibration is to apply the correct amount of spray mix to a given area of crop or land - in

litres/hectare (l/ha) or litres/acre, gallons/acre etc.

This is dependent on the following variables:

Student’s Manual For Level One and Two in Agriculture 133

The concentration of product in the water in the tank or dilution rate (usually measured in

gram/litre g/l) or millilitres/litre (ml/m))

The nozzle output or flow rate measured in litres/minute (l/min).

The spray width in metres - which is itself dependent on two factors: the

nozzle spray angle; and the height of the nozzle above the target

The walking speed of the spray operator (in mph, km/h or m/sec)

The above factors should be considered when calibrating your sprayer.

There are various ways of using the measurements made of the variables listed above to achieve the

correct output per unit area. What the farmer or spray operator needs to know is: flow rate, swath width,

usual walking speed, how much of a particular product needs to be added to the tank to achieve the

correct dilution rate (in litre or ml per tankful) to give the correct product rate for the whole area needing

treatment.

• Study the Directions for Use section of the pesticide label to find out how much pesticide you should

apply. If the labeling lists a range of possible amounts, use the least amount that will achieve good

control.

Sometimes consultants, industry organizations, pest or pesticide specialists, Cooperative Extension

agents, university specialists, or pesticide dealers will recommend appropriate amounts.

Student’s Manual For Level One and Two in Agriculture 134

PESTICIDE RESISTANCE

Repeated use of the same class of pesticides to control a pest can cause undesirable changes in the gene

pool of a pest leading to another form of artificial selection, pesticide resistance. When a pesticide is first

used, a small proportion of the pest population may survive exposure to the material due to their distinct

genetic makeup. These individuals pass along the genes for resistance to the next generation. Subsequent

uses of the pesticide increase the proportion of less-susceptible individuals in the population. Through this

process of selection, the population gradually develops resistance to the pesticide. Worldwide, more than

500 species of insects, mites, and spiders have developed some level of pesticide resistance. The

twospotted spider mite is a pest of most fruit crops and is notorious for rapidly developing resistance to

miticides.

Some plant pathogens have also become resistant to pesticides. Among fruit producers in North America,

apple growers perhaps have faced the most significant problems with pesticide resistance. Examples

Student’s Manual For Level One and Two in Agriculture 135

include streptomycin resistance in the fire blight bacterium and benomyl resistance in the apple scab

pathogen. Although the precise genetic and ecological factors differ among pests that have become

resistant, in all cases resistance is driven by one process -- selection.

Insecticide resistance

Selection for resistance can occur if a small proportion of the insect population is able to survive

treatment with insecticide. These rare resistant individuals can reproduce and pass on their resistance to

the offspring. If an insecticide with the same mode of action is repeatedly used against this population, an

even greater proportion will survive. Ultimately, the once-effective product no longer controls the

resistant population.

Fungicide resistance

Single-step pesticide resistance arises suddenly in the field. A single gene or physiological function

changes so that an individual becomes highly resistant to the pesticide. With just one or two sprays of the

pesticide, the population shifts from mostly sensitive to mostly resistant individuals. This is the process

by which populations of streptomycin-resistant fire blight bacteria and benomyl-resistant apple scab

bacteria rapidly developed in commercial orchards.

Multi-step pesticide resistance arises slowly in the field over many years. Rather than having distinct

groups of sensitive and resistant individuals, the population consists of individuals with a range of

sensitivities to the pesticide. With each pesticide application, those individuals at the more resistant end of

the spectrum survive and reproduce. Over the years, the proportion of the population that can survive a

pesticide spray increases, until that pesticide eventually becomes ineffective. This process is underway in

apple orchards where the sterol inhibitor (SI) fungicides have been used extensively to control scab. The

shift toward resistance leads to a gradual erosion of control.

Resistance management

Growers can help delay the development of resistance by applying pesticides only when they are needed,

by rotating between different chemical classes, and by using rates of pesticides within the labeled range.

Integrating non-chemical approaches such as pheromone mating disruption and cultural controls can also

help delay resistance.

Student’s Manual For Level One and Two in Agriculture 136

First Aid for pesticide

The first and most important step in first aid happens before anyone is exposed to a pesticide. That is, you

must read and understand the pesticide label to know what the risks are and to be able to act

accordingly. Labels provide information on preventing accidents, and the labels provide necessary steps

to follow should there be an accident involving chemicals.

Remember, treatment for one type of pesticide poisoning may aggravate or increase the harmful effects of

a different chemical. The only way to know which treatments are helpful and which may be harmful is to

read the label before a problem occurs.

Symptoms of Pesticide Poisoning

Coma

Convulsions

Headache

Pinpoint pupils

Blurred vision

Excessive tearing

Dizziness

Salivation

Sweating

Tightness in chest

Rapid heartbeat

Elevated blood pressure

Rashes

Reddening of skin

Vomiting

Abdominal cramps

Diarrhea

Tremors

Muscle twitching

Muscle weakness

Blisters

Student’s Manual For Level One and Two in Agriculture 137

Swallowed Pesticide

Swallowing a pesticide is a serious situation. The decision you must make with this accident is whether or

not to induce vomiting. Again, read the label and get immediate medical attention.

To care for the victim:

If pesticide is still in the mouth, wash it out with plenty of water.

Quickly but accurately read the First Aid section of the label again to see if the swallowed

chemical should be diluted. When swallowed, some chemicals should be diluted with water or

milk. Other chemicals should never be diluted; again, the label provides the information.

Check to see if vomiting should be induced. If vomiting is to be induced, turn the victim so that

he/she is kneeling forward and does not choke. Ipecac syrup can be used to induce vomiting. If it

is not available, put your finger in the victim's mouth and touch the back of the victim's throat. Do

not use salt water to induce vomiting or attempt to give liquids.

Do not induce vomiting if the victim is unconscious, because the victim could choke.

First aid for some chemicals includes giving activated charcoal after vomiting. (Activated

charcoal adsorbs many poisons and is available without a prescription. It is a powder mixed with

water and given to the victim to drink.) Do not give activated charcoal and ipecac syrup at the

same time; the charcoal adsorbs the syrup, and any good effects are wasted.

Keep the victim calm and take him/her to the hospital. Also take the product label and any

Material Safety Data Sheets you have about the swallowed pesticide.

Inhaled Pesticide

An inhaled pesticide presents a different problem but is just as serious. Breathing a pesticide can hurry the

effects of poisoning--quick action is a must.

Get the victim to fresh air.

Calm the victim, and have him/her lie down.

An inhaled pesticide can cause convulsions, so protect the victim's head if convulsions occur.

Keep the victim's air passage clear. Tilt the head back to keep the passage open. Remove any

foreign object or matter from the victim's mouth.

If the victim stops breathing, begin artificial respiration and continue until he/she breathes again

or until you reach the hospital. (A Red Cross course is helpful in learning CPR.)

Student’s Manual For Level One and Two in Agriculture 138

External Skin Exposure

The hands and forearms account for 95 percent of all skin exposures. Usually these exposures are caused

by splashes or spills that occur while mixing the chemicals.

If a chemical gets on your skin:

Immediately remove all contaminated clothing;

Wash the exposed area with generous amounts of water and soap;

Use a brush and soap to remove residues from under your fingernails;

If your hair is contaminated, shampoo well;

Put on fresh, clean clothes;

See a physician.

Whenever the pesticide application is completed or interrupted for a time, follow these same steps

whether or not you were accidentally exposed. Follow the same steps before going home. Do not expose

your family to the pesticides you have used during the day. (A child's skin is more sensitive to chemicals

than is an adult's.)

Eyes

If you splash any chemical into your eyes, immediately wash out your eyes with plenty of cool, clean

water. Wash at least 15 minutes to help prevent eye damage. Some chemicals can permanently damage or

even blind you in less than 2 minutes. For just such emergencies, set up an eyewash station or keep an

eyewash bottle in your first aid kit. Do not wash out the eyes with any water containing drugs, because

this could aggravate the situation. Seek medical attention immediately.

At Hospital or Doctor's Office

Remember to take the pesticide label to the medical staff, because the label contains specific instructions

for doctors to use in treating poisoning emergencies. It can be difficult to run medical tests to determine in

a short time the type of chemical exposure the victim has experienced. These tests use valuable time that

could be used to treat the victim.

Student’s Manual For Level One and Two in Agriculture 139

Prevention

You need to have a well-stocked first aid kit to use in case of a pesticide poisoning or any other medical

emergency. Consult the following list to check your first aid kit or, if you are starting from scratch, to

make up an emergency first aid packet.

Eyewash bottle

Plenty of clean water

Syrup of ipecac

Activated charcoal powder

Soap

Disposable towels

Clean change of clothes

All pesticides have the potential to cause bodily harm, but used properly, they pose no special hazard.

Always read the label and follow all instructions when using any chemical.

Student’s Manual For Level One and Two in Agriculture 140

Module 13.1

Diseases of crops

A disease causes a disruption in the normal physiology, or functioning, of a plant, usually with a negative effect on

the growth and productivity. This is normally caused by a causal organism. Affects of insects and mites are not

considered as diseases. The prevention and diagnosis of diseases are important to minimize crop losses. The

fundamentals of plant diseases and their management are presented in this chapter. Topics include an introduction to

the types of pathogens and their effects, how diseases are caused, disease diagnosis and management, and the major

plant diseases in the Maldives, and control measures. Due to diseases there could be a partial, and in extreme cases

even total failure of the crop. It could also lead to a lower quality product which could have an impact on marketing,

especially if it is expected to market the produce to the resorts. Build up of disease organisms could also lead to the

inability of growing a particular crop, even though it may have a high demand. A high incidence of diseases

increases the cost of production due to the greater cost of control measures.

Nutritional Methods of Pathogens

Bacteria and fungi secrete enzymes and degrade material (enzymatic degradation), of the host externally as opposed

to internal digestion that takes place in animals. This process is called absorptive nutrition and it is degradation that

takes place outside the pathogen. Nematodes use enzymatic and bacterial-mediated degradation inside the pathogen

which is alimentary nutrition. Viruses do not have a nutrition phase.

Obligate and Non-Obligate Pathogens Obligate pathogens are those who can live only on a certain range of host plants. They cannot be actively alive on

other plants or on dead organic matter. Non-obligate pathogens can

survive on their dead host. They can also survive and grow on a number of other organic materials.

Disease management could differ in terms of whether the pathogen is obligate or non-obligate.

How Pathogens Cause Disease

Pathogens cause disease in a number of different ways. These are given below:

1. Enzymatic degradation Host tissue is broken down due to the enzymes that are secreted by the

pathogen. The destruction of different tissues in the plant leads to different diseases.

2. Toxins Toxins are harmful chemical that are produced by the pathogen. The toxins produced by a

pathogen will kill the plant tissue. Very often this could be done before enzymatic degradation. In many

cases much of the damage to a plant, especially with non-obligate pathogens, is caused by toxins.

3. Growth regulators Growth regulators are substances such as hormones which have an impact on the

growth of the plant. Pathogens produce growth regulators on their own, or they could also cause the host

plant to produce them. As a result of the production of growth regulators, translocation of nutrients to host

cells could take place. Translocation of nutrients is the movement of nutrients from one place in a plant to

another. Growth regulators could also cause the host cells to enlarge or divide in the areas close to the

pathogen. Due to the above, the availability the food to the pathogen is increased. This technique provides

additional food for the pathogen without killing the plant.

Student’s Manual For Level One and Two in Agriculture 141

Causal Organisms

Fungi A fungus is multi cellular and the cells have a nucleus. Their size is not limited. Fungi have

different structures such as spores. Similar to bacteria most fungi are also saprophytic. Plants affected by

fungi could show signs of rot, blight, leaf spots, and wilt. Similar to bacteria fungi are also very sensitive

to light and dry conditions. However, they can make very resistant structures in order to survive. Fungi

spread by wind, water, seed, and vectors. People also can spread these spores by carrying them on their

hands, shoes, tools or clothing. Examples of fungal diseases are anthracnose and powdery mildew.

Bacteria

Bacteria is single celled, and have no nucleus. Bacteria are so small that they can only be seen with a

microscope. Their reproduction is unlimited and thus they reproduce faster than fungi. Thus the spread of

bacterial diseases could be quicker than that of fungal diseases. However, they do not cause as many

serious problems as fungi. They show absorptive nutrition and are mostly saprophytic. Bacteria causes

blights (quick killing of plant tissue by toxins), rots (breakdown of plants with a ‗mushy‘appearance),

wilts (blocking of the systems transporting water), and galls (enlarging of plant parts due to growth

regulators).

Active bacteria are very sensitive to the environment and could be affected greatly by sunlight and drying.

In an inactive stage they survive harsh conditions. They can rest in the soil for a long time, and begin to

grow and multiply when the correct type of plant is grown again. Bacteria are spread by wind, water,

seeds and vectors. Vectors are normally insects which carry the pathogen from one source to another. An

example of a recent bacterial disease seen in Maldives is bacterial fruit blotch in water melon.

Viruses

Viruses are pieces of RNA or DNA. RNA and DNA are nucleic acids, which are all components of the

nucleus of a cell. Viruses are always parasites. The virus takes over the normal functions of a cell. It

upsets normal metabolism, which are the activities of a cell, and causes an additional increase or a

shortage of molecules needed to make new components, or parts, in cells. As a result abnormalities are

seen in the plant tissues. These could be seen as mosaics, yellows, distortion and death. Viruses spread by

seeds or vectors like aphids, mites and white flies. The control of vectors is very important in the control

of viral diseases. They can also spread with infected planting material. Hence, it is very important to use

virus free planting material. An example of a viral disease is the Cumber mosaic virus.

Student’s Manual For Level One and Two in Agriculture 142

Oomycetes

Oomycetes are similar to fungi in many ways. Oomycetes produce zoospores (mobile spores) and

oospores. Most live in water or soil. They prefer free water or a film of water in which they can swim.

Oomycetes are spread by wind, water, seeds, and vectors. Examples are downy mildew, and damping off

(Pythium), and Phytopthera root rots..

Nematodes

Nematodes are worms that are very minute and can only be seen under a microscope. Some of them have

only the head inside the plant (ecto-nematodes), and the others live totally inside the plant (endo-

nematodes). They could be in one place (sedentary) or may move (migratory). The plant‘s metabolism is

upset by the saliva of the nematode, leading to either to an excess or shortage of nutrients or hormones.

Symptoms could include tumours and the death of affected parts. Nematodes are seen mostly in sandy

soils and warmer conditions. They spread slowly. They are carried by water or humans. The root knot

nematode is an example of this kind of disease. Phytoplasmas

These are like bacteria without a cell wall. They are found only in the sap of plants. These are spread by

grafting or by insects.

Abiotic

Plants are also affected by the deficiency of the nutrients required by a plant. And sometimes these are

also called a disease and called a biotic diseases, which indicates that they area caused by non-biological

causes. However it is preferable to restrict the term ‗disease’ to the occurrences due to biological

organisms.

Disease Diagnosis

A doctor can treat a patient effectively only after he, or she, has diagnosed the disease. If the diagnosis is

not correct even the most expensive medicine will not cure the disease. Similarly in agriculture too, it is

important to correctly identify the disease so that the appropriate measures can be taken. The following

are measures that could be taken to help in the identification of diseases.

1. Pattern of disease in the whole field

The pattern of disease in the field could provide some guidance in identifying the disease. See whether

patterns could be identified. The patterns that may be seen could include plants affected in a circular

patch, plants affected down a row, or across a row. Such a pattern could indicate how the disease is

spreading. The border between the affected plants, and the healthy plants would be the area where most of

the current pathogen activity is. When looking for signs of current activity these areas should be observed.

Student’s Manual For Level One and Two in Agriculture 143

2. Symptoms and signs

A good way of trying to identify a disease is to look at symptoms and signs. These are two different

aspects. Symptoms are what could be observed as a response of the host due to the infection by a

pathogen. For example, the discoloration of a leaf could be a symptom. A sign is a visible structure of the

pathogen itself. A sign is more diagnostic in comparison to a symptom. All the different symptoms and

signs should be observed. Keep in mind the diseases that are locally common. These symptoms should be

compared to pictures. However, it should be noted that in some instances, more detailed laboratory tests

may be needed to correctly identify the disease. In such instances, in many countries, samples taken from

the field would be sent to the laboratory for identification of the disease.

10.6 Plant Diseases in the Maldives

It is estimated that there are approximately 45 plant diseases affecting crop, ornamental and forest plants

in the Maldives. The major fungal, bacterial, and viral diseases affecting crops in the Maldives are

Name of

symptoms

Disease

Anthracnose Have characteristics dark necrotic spot and lesions. The lesions are frequently

sunken. Fruits and leaves are commonly attacked.Colletotrichum sp. Is common

fungus that cause anthracnose in the Maldives

Blights Rapid and extensive death of certain areas of the plant. Leaf and fruit blights are

common in the Maldives

Black leg Blackening and rotting of the stem base

Damping off Disease of seedlings, seedlings collapse and die. Affect root tips and

roots.Pythium,Rhizoctonia and Phytopthora genera of fungi are responsible.

Rots Large necrosis of plant tissue, often affecting the complete organ. Can be due to

number of fungi

Powdery mildew Prominent white cottony growth on the upper side of the leaves

Downy mildew Black sporulation on the under side of the leaves

Sooty mould Blackish powdery growth all over the plant

Leaf/fruit spots Caused by a number of fungi. Brownish spots develop on leaves, stems and fruits

Student’s Manual For Level One and Two in Agriculture 144

Leaf blight Fruit rot

Downey mildew Sooty mould on Guava

Cercospora leaf spot-early stage Cercospora leaf spot- Later stage

Student’s Manual For Level One and Two in Agriculture 145

Fusarium wilt Rust

Two main bacterial diseases affecting crop plants in the Maldives

Name of disease Plant Attacked Symptoms

Citrus canker Bacteria Citrus Die back of plants

Bacterial soft Rot Watermelon Soft rot of fruits

Major viruses that affect crop plants in the Maldives

Type of virus Plant Attacked Symptoms

Banana Bunchy Top virus Banana Leaves of infected trees are short and

narrow with an upward curved margin

Leaf Curl virus transmitted by

thrips,mites and aphids

Chilly Curling of leaves, leaf development

suppressed. Bronze appearance on

leaves.

Cucumber Mosaic Virus

transmitted mostly by aphids

Cucumber, Pumpkin

and other cucurbits

Inter-veinal mosaic at leaf edges.

Plants stuned

Watermelon Mosaic Virus Watermelon Severe leaf distortion and mosaic

Student’s Manual For Level One and Two in Agriculture 146

Fungicide used

Disease Fungicide Dilution

Powdery mildew Sulphur

Blast, stem rot, powdery

mildew, anthracnose

Copper oxychloride

Cercospora,alternaria

rust,downey mildew

Propineb 10 gm

Blight, damping off Captan 12.5 gm

Cercospora,alternaria,rot,blight Mancozeb 10 gm

Bacterial Diseases

Antibiotics, though available in some countries for application to plants, are not recommended for use in

the Maldives. Thus, prevention of bacterial diseases, and destruction of affected plants, if so

recommended, is very important.

Viral Diseases

In general drugs are not available against viral infections in humans. Similarly in plants too no pesticides

are available for use once a viral infection has occurred. Hence, as in bacterial diseases, it is very

important that steps be taken to prevent the occurrence of viral diseases. Steps to be taken to prevent

diseases in general are applicable for the control of viral disease and are discussed in the following

section.

Ecological Disease Management

It is important that all three components of the disease triangle be fulfilled for a disease to occur. Thus it

is important to try and prevent the occurrence of disease, and not only try to only control it once it has

occurred. In general healthy plants are more resistant to disease, even as healthy people are more resistant

to infections. Plant susceptibility is also dependent on the level of stress of the plant. Farmers can

manipulate the disease triangle in order to minimize the incidence of disease. Minimizing the use of

pesticides by following the practices given below would also help to reduce problems that could arise by

large amounts of pesticide. These problems could be removal of natural enemies that were controlling

other pest problems, build up of resistance in pests, toxicity to plants, and also the high cost of pesticide

use.

1. Environment manipulations

The farmer has a certain amount of control over the crop environment. For example, plant spacing could

be increased to increase air circulation and falling of sunlight, thereby reducing humidity and hence plant

infection. The possible need for such measures will have to be balanced by the need for higher plant

populations for greater yields if appropriate. Hence the optimum conditions could very according to the

specific situation. Other examples of environmental manipulations include regulating the amount of

irrigation and drainage, and determining on which location the crop is grown (e.g. low water table or high

water table).

Student’s Manual For Level One and Two in Agriculture 147

2. Host manipulations

Depending on the circumstances steps should be taken to minimize the susceptibility of the host. Specific

practices that could be adopted to achieve this are as follows:

Use crops appropriate for that environment. For example, in the water logged areas do not grow

crops such as pumpkin. it can be seen that the water table is very high, and also that the crop has

been affected as seen by the plants right in front. Instead grow crops such as taro

Use resistant varieties. For example, the Red Lady variety of papaya is resistant to papaya

ring spot virus.

Use pathogen free planting material

From trusted sources

By seed / planting material treatment

Use crop rotation where plants from the same family are not grown in consecutive seasons on the

same plot of land. Thus after a chillie (Family: Solanaceae) crop, either chilly or some other crop

from the same family such as brinjal or tomato, should be not be grown on the same plot of land.

When the host is changed like this, the effect of the pathogens that have built up is reduced.

3. Pathogen manipulations

It is important to minimize levels of the pathogen. This is done by the following. Manually

removing the host tissue which harbours the pathogens, and destroying it appropriately like

burning. Use chemicals such as copper, sulphur, potassium bicarbonate fungicides or bio-

pesticides such as neem if recommended. Efforts are also being made to understand the role of

non-pathogenic microbes in the management of diseases.

4. Climate and weather patterns that encourage the rate of growth, development, and distribution

of certain plant pathogens

Generally plant pathogens grow well under conditions that are wet and warm, with free moisture

on plant surfaces. However, some pathogens, such as powdery mildew, are inhibited by rainfall

and overhead irrigation such as hose irrigation could be used to control such diseases. However,

others such as Anthracnose need rain to spread their spores. Some pathogens are spread by wind

(powdery and downy mildews), and some diseases need both wind and rain to spread.

Stress caused on the plant by unfavorable growing conditions will lead to greater susceptibility to

diseases.

In general it is important to match the crop‘s requirements to the agro-climatic environment to

minimize disease. In the Maldives this matching is more relevant at the micro-climate level.

Often in small scale production the micro-climate is changed to meet the requirements of the

crop. This is accomplished by the covering with cadjans, on both the sides and top, to reduce the

effect of wind and thereby humidity and evapo-transpiration as well as the level of sunlight.

Student’s Manual For Level One and Two in Agriculture 148

Module 13.2

Fungicides

A fungicide is a chemical pesticide compound that kills or inhibits the growth of fungi . In agriculture,

fungicide is used to control fungi that threaten to destroy or compromise crops. Gardeners use fungicide

as a household pesticide to protect plants from potential destruction. In medicine, fungicide is used to kill

fungal infections . The drugs used to kill these infections are referred to as antifungal drugs.

Fungicides have been used for more than 400 years from as simple as a brine solution, which was used for

cereal seed treatment, to the introduction of very complex organic chemical compounds in the earlier half

of the 20th century. There are different classes of fungicides that are classified according to their chemical

structure. One of them is copper-based fungicides or copper fungicides. It has been used to protect crops

after the ‘accidental’ discovery of the Bordeaux mixture by Pierre-Marie-Alexis Millardet in the late

1800s.

Disease control with the use of a copper based fungicide is done by disrupting the functions of the cellular

proteins of fungi and bacteria. This is because when cupric ions are released in the presence of moisture,

it destroys the secondary and tertiary structures (denaturation) of these proteins upon contact. Once these

proteins are denatured, its functions are lost.

Copper is an essential micro element needed by plants. It is an important component of proteins found in

some enzymes which are involved in regulating some biochemical reactions. Copper is also responsible

for chlorophyll formation and promotes seed production and formation. Excess concentration especially

on the roots can largely affect as growth and morphology.

In the Philippines, the common copper based fungicides are copper oxychloride, copper hydroxide and

cuprous oxide. Nordox 50 WP is the only copper fungicide in the market with cuprous oxide as its active

ingredient. It is a broad spectrum fungicide used not only to kill different fungi but bacteria as well. It also

breaks the resistance of these pathogens wherein it disrupts the disease build up in an area where there is a

history of infection. Nordox 50 WP is produced in Norway by NORDOX AS, the worldleading producer

of superior cuprous oxide for agrochemical use. It is super micronized with particles slightly larger than 1

micron that is why it is very effective in preventing and controlling the development of fungi.

Particle size and solubility with copper fungicides, the effectivity to control fungi and bacteria is not determined by the number of

applications per area or how many grams of active ingredient were applied, rather it depends on how long

it retains on the plant surface. The longer it is retained the more effective it is in controlling pathogens.

The particle size of Nordox 50 WP is only 1.2 microns while copper hydroxide and copper oxychloride is

1.8 and 2.5 microns, respectively. Given its fine particle size, it gives a more uniform dispersion when

mixed in water as compared to other fungicides. With even dispersion, the active ingredient is not settling

at the bottom of the sprayer giving a more uniform application from the very start of application up to the

last drop of the mixture. Since Nordox 50 WP is very fine, it has higher surface contact, so it can adhere

longer on the plant surface giving better protection. This is the other two copper fungicides which have

tendencies to settle and give an inconsistent mixture and can be easily removed by rain and wind when

applied on leaves. The other copper fungicides with larger particles are easily removed from the leaf

surface by rain or wind and then accumulate in the soil injuring the roots which adversely affects plant

growth.

Student’s Manual For Level One and Two in Agriculture 149

Another criterion to consider aside from the size of the particle is the solubility of the copper fungicides.

This is because solubility determines the release rate of cupric ions. The copper in Nordox 50WP are

more insoluble than the two copper fungicides. Being more insoluble, it provides a slower, controlled

release of cupric ions on the leaf surface providing the plant longer, more cost efficient protection

compared with other fungicides. If the copper source is very soluble, there is a tendency of releasing too

many cupric ions that can damage the leaf.

Economics Nordox 50WP is the cheapest copper fungicide in the market. It comes in a 1 kilogram box with a

suggested retail price of Php600.00 and a recommended rate of 2 grams per load. Each load would cost

about Php11.00 to Php17.00 depending on the rate. Although its price is almost the same as the other

fungicides, the cost per knapsack load is cheaper and you save about 9% as compared to copper

hydroxide and 118% as compared to copper oxychloride. These savings can be doubled or tripled

especially during rainy season because with other fungicides, there is a need for a sticker and

reapplication since these can be easily washed off by rain. Reapplication means added production costs.

With Nordox 50WP, once you have applied it, you are certain that it stays there to give your plant better

protection against diseases caused by fungi and bacteria.

Chemical based fungicides

Mancozeb It is a grayish-yellow powder with a musty odor usually insoluble in water as well as other organic

solvents. Mancozeb is a polymer of maneb combined with zinc, has low acute toxicity to mammals and is

not poisonous to plants.

Tricyclazole It is a systemic fungicide used for controlling blast disease of rice and preventing rice spike and leaf

paste. Tricyclazole is a new fungicide having high effect, low toxicity, low residue and is effective to

control rust, powdery mildew and anthracnose on beans.

Carbendazim It is a systemic benzimidazole fungicide that plays a very important role in plant disease control.

Carbendazim is used for controlling a wide range of pathogens and as a preservative in fruit industry,

textile, paper making, leather and paint industry.

Hexaconazole It is a systemic, broad-spectrum fungicide with protective and curative action. Hexaconazole is mainly

used on bananas, cucurbits, peppers and other crops.

Metalaxyl It is a systemic, benzenoid fungicide used in mixtures as a foliar spray for tropical and subtropical crops.

Metalaxyl is also used as a soil treatment for control of soil-borne pathogens and as a seed treatment to

control downy mildews.

Benomyl It is a systemic, benzimidazole fungicide that is selectively toxic to microorganisms and invertebrates,

particularly earthworms. Benomyl is used against a wide range of fungal diseases of field crops, fruits,

nuts, ornamentals, mushrooms, and turf.

Difenoconazole It is a broad-spectrum inhalation fungicide mainly used to protect and cure basidiomycetes and comycetes

Student’s Manual For Level One and Two in Agriculture 150

fungi in leaves or seeds of grape, peanut, potato, wheat and vegetables.

Propiconazole It is a systemic foliar fungicide with protective and curative action. Propiconazole is used as a biocide

against blue stain in wood preservatives and compounding with triazoles and pyrethroids in exterior

varnishes.

Kitazin Kitazin is a broad spectrum systemic fungicide belonging to the organophosphorus group for the control

of various diseases such as blast and sheath blight of rice, fruit rot of chilli, early blight of tomato and

potato, purple blotch of onion, anthracnose of grapes and pomegranate etc.

Tebuconazole It is a fungicide used for the control of smuts, bunt, seed rots and seedling blights on barley, oats and

wheat as a seed treatment. Also used for the control of fusarium head blight on wheat as a post-emergent

treatment.

Copper oxychloride It is a kind of fungicide which is effective and used for the control of fungus diseases of fruit trees, vines

and vegetables, also helps in preventing black spot on apples, pears, tomatoes and citrus fruits .

Copper hydroxide It is an excellent protective fungicide of blue color killing both fungi and bacteria. Copper hydroxide is

widely used and applied in the agriculture industry to prevent agricultural crops from contracting diseases

including copper deficiency.

Tridemorph It is a systemic fungicide used widely over numerous crops in many countries around the world.

Tridemorph is used to control the fungus Erysiphe graminis in cereals, Mycosphaerella species in

bananas, and Caticum solmonicolor in tea.

Propineb It is a basic foliar fungicide with protective action used on citrus fruit , berry fruit, rice ,tea and to control

downy mildew, black rots, red fire disease, and grey mould on vines; scab and brown rot on apples and

pears and leaf spot diseases on stone fruit.

Organic type of fungicides.

Safin We produce two varities of Safin, one is an organic derived from natural extracts of Allicin & Calotropin .

The other one is 6G Safin derived from 6%granules. Safin is toxic free and control wide range of fungi

and nematodes with a long standing period of action. For more information, click on the lonk below:

Sporrin There are two types of Sporrin manufactured by us , one is a natural organic derived from natural extracts

of triterpenes & alkaloids . The other one is Sporrin 6G derived from 6% granules. Sporrin is a potential

fungicide & bactericide used for controlling diseases like powdery mildew, downy mildew, rot,

anthracnose, wilt, leaf spot, cankers, early & late blight etc.

Student’s Manual For Level One and Two in Agriculture 151

Blastin

Two categories of Blastin are produced by us. One is a natural extract of monoterpene, G-terpinene &

Alkaloids and the other one is Blastin 6G derived from 6% granules

BioVitrioll

It is a fungicide which is based on Organic Copper.

Sulphur Fungicides

Sulphur undoubtedly the oldest of all pesticides. It may be mined or scrubbed from natural gas. It is a low

toxicity material, compatible with many other insecticides and fungicides and may be used in

combination with GREEN EARTH pyrethrins and/or rotenone products.

Garden Sulphur is available as a ready to use spray or a wettable powder. The particle size of the wettable

powder is also fine enough (325 mesh) for effective use as a ready to use dusting powder.

Sulphur is considered non-toxic to man, animals and bees. It may be used throughout the growing season

and up to one day before harvest on all crops except grapes grown for wine.

Sulphur is toxic to fungi such as powdery mildew, rusts, black spot, apple scab and stone fruit diseases.

An added benefit is its ability to control or prevent build up of mite population

MANCOZEB 75% W.P.

Brand Name :

Starmet 75% W.P.

Chemical Composition :

Mancozeb tech 88.23% w/w

Suspending agent (gum) 2.00% w/w

Dispersing agent (alkyl naptha sulphonate) 2.00% w/w

Surface active agent (sodium salt of alkyl aryl sulphonate) 2.00% w/w

China clay 5.77% w/w

Application : Crop: Paddy, Wheat, Potato, Cauliflower, Groundnut, Grapes, Chilies, Apples, Banana, Ginger, etc.

Use : It is used of control to brown and black rust, blight of wheat, leaf blight etc.

HEXACONAZOLE 5% EC

Brand Name :

Hexastar 5% EC

Chemical Composition :

Hexaconazol tech. (based on 92% purity) 5.5% w/w

Student’s Manual For Level One and Two in Agriculture 152

Emulsifiers

-Styrinated phenol ethylene oxide condensate 5.0% w/w

-Dodecyl benzene sulfonicacid calcium salt 5.0% w/w

Solvent (Aromex or xylene) 84.5% w/w

Use: It is used for control of scale, blast, sheath blight, tikka, leaf spot etc.

SULPHUR 80% WP

Brand Name:

Super star 80% WP

Chemical Composition:

Sulphur Technical (based on 99.5% w/w ) 80.4% w/w

Dispersing agent - an salt witting suspending agent 5.0% w/w

China clay 14.6% w/w

Total 100% w/w

Use: It is used for control of powdery mildew, tikka leaf spot etc.

SULPHUR 85% DP

Brand Name:

Super star 85% DP

Chemical Composition:

Sulphur Technical (based on 99.99% w/w ) 85.43% w/w

Soap stone powder 14.57% w/w

Total 100% w/w

Use: It is used for control of powdery mildew, tikka leaf spot etc.

Lime Sulphur Fungicide/Insecticide

Description: Concentrated lime sulphur solution for control of certain diseases, insects and mites on

pome fruit, stone fruit, citrus, grapes, roses, hedges and vegetables.

Sizes: 500ml, 1L, 5L, 20L, 200L.

Area Treated: Rates vary depending on crop and state registration. Citrus is 10L/100L. Pome fruit is

5L/100L.

Student’s Manual For Level One and Two in Agriculture 153

Diseases Controlled: White Louse Scale, Mouri mite, Bud mite, Erinose mite, Vine Bunch mite, San

Jose scale, Byrobia mite, Pear leaf blister mite, Frosted scale, Two spotted mite, Tomato mite, Powdery

Mildew, Rust, Brown Rot, Black Spot, Shot hole, leaf curl and Freckle.

Contains: Polysulphide Sulphur.

Where to use: In crops mentioned and at the registered rate.

When to use: Follow critical comments on the product label. Timing depends on the crop and the pest or

disease.

Use rate: Rates vary fro 1L/100L of water to 10L/ 100L.

Useful Tips:

Do not apply during growing period of apricots, raspberries, cucurbits, peaches or other sulphur sensitive

plants. Suitable to be included in a resistance strategy. Do not mix with water of pH below 4. Spread of

mites is checked by sulphur treatments used for powdery mildew. Use spray mixture on the same day as

mixed with water.

Main Usage Period: Mainly when the trees are dormant.

Antibiotics

Antibiotics are mainly used against bacterial plant pathogens. Some of the promising antibiotics are

streptomycin sulphate, streptocycline, terramycine, and agrimycin-100.

Plant uptake was evaluated in a greenhouse study involving three food crops: corn, lettuce, and potato.

Plants were grown on soil modified with liquid hog manure containing Sulfamethazine, a commonly used

veterinary antibiotic. This antibiotic was taken up by all three crops. Concentrations of antibiotics were

found in the plant leaves. Concentrations in plant tissue also increased as the amount of antibiotics present

in the manure increased. It also diffused into potato tubers, which suggests that root crops, such as

potatoes, carrots, and radishes, that directly come in contact with soil may be particularly vulnerable to

antibiotic contamination.

The ability of plants to absorb antibiotics raises the potential for contamination of human food supply can

render antibiotics ineffective.

A wide range of food crops and ornamental plants are susceptible to diseases caused by bacteria. Bacterial

diseases of plants are notoriously difficult to control and often result in sudden, devastating financial

losses to farmers. In the 1950s, soon after the introduction of antibiotics into the field of human medicine,

the potential for these "miracle drugs" to control plant diseases was recognized. Unfortunately, just as the

emergence of antibiotic resistance sullied the miracle in clinical settings, resistance has also limited the

value of antibiotics in crop protection.

In recent years, antibiotic use on plants, and in particular the potential impact of this practice on human

health, has been fiercely debated in several countries. This article will focus primarily on the situation in

the United States, where I have been best able to access antibiotic use data and research reports. The

objectives of this article are to

Student’s Manual For Level One and Two in Agriculture 154

i) present the practical and political aspects of antibiotic use on plants;

ii) present special aspects of plant use that may impact the development and persistence of antibiotic

resistance genes in agro ecosystems;

iii) challenge agencies that have traditionally been parochial in their funding to view antibiotic resistance

as a universal phenomenon in need of multidisciplinary research and education.

Practical and political aspects.

The diversity and quantity of antibiotics used for plant disease control is meager compared to medical and

veterinary uses. In the United States, streptomycin is registered for use on twelve fruit, vegetable, and

ornamental plant species; oxytetracycline is registered for use on four fruit crops Both antibiotics are

applied primarily for the control of bacterial diseases, although streptomycin is also used to a limited

extent to control diseases caused by water molds, and oxytetracyline has been used to control certain

diseases caused by phytoplasmas (mycoplasma-like organisms that infect plants).

Antibiotics are among the most expensive of pesticides used by fruit and vegetable growers, and their

biological efficacy is limited, many growers use weather-based disease prediction systems to ensure that

antibiotics are applied only when they are likely to be most effective. Growers can also limit antibiotic

use by planting disease resistant varieties and, in some cases, using biological control (applying

saprophytic bacteria that are antagonistic to pathogenic bacteria). Despite these efforts to reduce growers’

dependency on antibiotics, these chemicals remain an integral part of disease management, especially for

apple, pear, nectarine, and peach production.

Antibiotic use on crops and ornamental plants in the U.S. is regulated by the Environmental Protection

Agency. Product labels and supplemental literature clearly state what type of clothing, boots, gloves, and

respirators must be worn by mixers, applicators, and persons entering a treated area after antibiotics have

been applied. These documents are legally binding, and it is a violation of federal law to use an antibiotic

in a manner inconsistent with its labeling. In addition to federal laws, states have pesticide laws and help

enforce the federal mandates. Thus, although the application of antibiotics to plants is markedly different

from clinical use and may appear to occur under uncontrolled conditions (i.e., the open environment), it is

a highly regulated activity; farmers are bound by stringent measures to protect the health of workers and

the environment.

Given these seemingly rigid regulations, does antibiotic use on plants pose risks to human health? One

consumer advocacy group has argued that applying antibiotics to crops is an imprudent luxury that may

eventually lead to the demise of life-saving drugs Growers, however, defend their practice as being so

limited in scope as to be inconsequential to human and environmental health. Unfortunately, both sides

lack of sound, quantitative data to uphold their positions. For now, this leaves us with a contentious

debate based on circumstantial evidence and fueled by passion. On the one hand, fruit and vegetable

producers have sizable economic interests (including their very livelihoods) at stake when dealing with

bacterial diseases. The amount of antibiotics used in plant disease control is minuscule compared to total

use, and no apparent human health issues have arisen after four decades of use. On the other hand,

medical experts have witnessed the failure of one antibiotic after another in clinical settings which, at

least superficially, appear to be much more confined and strictly controlled than farm settings.

Student’s Manual For Level One and Two in Agriculture 155

Special aspects of antibiotic use on plants.

Although antibiotic use on plants is minor relative to total use, application of antibiotics in the

agroecosystem presents unique circumstances that could impact the build up and persistence of resistance

genes in the environment. The following scenarios are presented to provoke interest and possibly spark

research enterprises, not to condemn current agricultural practices or provide ammunition for those

seeking to ban the use of antibiotics for plant disease control.

First, antibiotics are applied over physically large expanses. In regions of dense apple, pear, nectarine, or

peach production, antibiotics are applied to hundreds of hectares of nearly contiguous orchards.

Moreover, the past decade has seen a dramatic increase in the planting of apple varieties and rootstocks

that are susceptible to the devastating bacterial disease, fire blight. This has created a situation analogous

to clinical settings where immune-compromised patients are housed in crowded conditions—settings

associated with the proliferation and spread of antibiotic-resistance genes.

Second, the purity of antibiotics used in crop protection is unknown. Reagent and veterinary grade

antibiotics have been found to contain antibiotic resistance genes from the producing Streptomyces spp.

Plant-grade antibiotics are unlikely to be purer than those used for treating animals and may themselves

be an origin of antibiotic-resistance genes in agroecosystems. The genes that were amplified from

antibiotics, otrA and aphE, are different from the resistance genes strA and strB that have been described

in plant-associated bacteria Thus, it may be that plant-grade antibiotics are a potential origin of resistance

genes in the environment but are not necessarily present and active in plant pathogenic bacteria.

Third, fertilizers and fungicides applied throughout the growing season are rich sources of divalent

cations. The concentration of Mn2+ or Ca2+ in these products is on the order of 10-50 mM, the

concentration used for chemical transformation of bacteria in the laboratory. Also, the commercial

formulation of oxytetracycline (Mycoshield) is a calcium complex. Although natural transformation has

been documented for only a few bacterial species, the concurrent application of antibiotics (with

resistance genes) and unnaturally high concentrations of divalent cations might promote chemical

transformation in planta. DNA is tightly bound by aminoglycoside antibiotics, such as streptomycin,

which could protect the DNA from nucleases and even enhance its uptake into bacterial cells .Once

introduced into the bacteria, the resistance genes would have to be integrated into the bacterial genome by

illegitimate recombination, an inefficient process. However, if bacteria acquired resistance genes, even at

very low frequencies, exposure to antibiotics would provide the selection pressure needed to convert the

initially rare strains into a predominant component of the population.

The challenge for granting agencies.

The evolution of antibiotic resistant bacteria is outpacing the discovery of new antibiotics. Fruit and

vegetable growers struggle to maintain the registration and efficacy of the only two antibiotics at their

disposal. This political battle comes on the heels of the Food Quality Protection Act of 1996, a pesticide

law that threatens the registration of several pesticides that fruit and vegetable growers depend on to stay

in business. Thus, the stakes are high for both human medicine and food production. Knowledge of the

origins and acquisition of antibiotic resistance genes in the environment is central to developing strategies

to retain the efficacy of antibiotics to control diseases of humans, animals, and plants. But how will this

knowledge develop? There is certainly no shortage of intellect or scientific expertise in the field of

antibiotic resistance. Rather, the gap appears to be in joining experts from different disciplines and then

persuading granting agencies that have traditionally funded either medical or agricultural research to

recognize antibiotic resistance for the global and multidisciplinary phenomenon it is.

Student’s Manual For Level One and Two in Agriculture 156

Antibiotic Formulation Trade name(s) Primary uses

Streptomycin 22.4% streptomycin

sulfate; equivalent to

17% streptomycin

Agri-mycin 17 Apple, pear,

ornamental plants,

tomato, pepper, potato

Oxytetracycline 31.5% oxytetracycline

calcium complex;

equivalent to 17%

oxytetracycline

Mycoshield;Agricultural

Terramycin

Peach and nectarine,

pear, apple