Problematic Soils and their Management (New) Credit Hours: …jnkvv.org/PDF/07042020182543Soil Health.pdf · 2020. 4. 7. · Problematic Soils and their Management (New) Credit Hours:

Problematic Soils and their Management (New)Credit Hours: 2(2+0) (Midterm 40 marks + Assignment 10 marks)

TheorySoil quality and health, Distribution of Waste land and problem soils in India. Theircategorization based on properties. Reclamation and management of Saline and sodic soils,Acid soils, Acid Sulphate soils, Eroded and Compacted soils, Flooded soils, Polluted soils.

Irrigation water – quality and standards, utilization of saline water in agriculture. Remote sensingand GIS in diagnosis and management of problem soils.Multipurpose tree species, bio remediation through MPTs of soils, land capability andclassification, land suitability classification. Problematic soils under different Agroeco systems.

Books: 1. Fundamental of Soil science ICAR Publication

2. D.K. Das Kalyani publications

3. Problematic Soils by P. R. Fleming, E. J. Murray, I. Jefferson, E. Faragher

Soil Quality ConceptsSoil quality is how well soil does what we want it to do. More specifically, soil quality is thecapacity of a specific kind of soil to function, within natural or managed ecosystem boundaries,to sustain plant and animal productivity, maintain or enhance water and air quality, and supporthuman health and habitation. Soil Organic Matter and Soil Biology play a major role in soilQuality.People have different ideas of what a quality soil is. For example:

For people active in production agriculture, it may mean highly productive land,sustaining or enhancing productivity, maximizing profits, or maintaining the soil resourcefor future generations.

For consumers, it may mean plentiful, healthful, and inexpensive food for present andfuture generations.

For naturalists, it may mean soil in harmony with the landscape and its surroundings. For the environmentalist, it may mean soil functioning at its potential in an ecosystem

with respect to maintenance or enhancement of biodiversity, water quality, nutrientcycling, and biomass production.

The Inherent and Dynamic Qualities of Soil

Soil has both inherent and dynamic qualities. Inherent soil quality is a soil’s natural ability tofunction. For example, sandy soil drains faster than clayey soil. Deep soil has more room forroots than soils with bedrock near the surface. These characteristics do not change easily.

Dynamic soil quality is how soil changes depending on how it is managed. Management choicesaffect the amount of soil organic matter, soil structure, soil depth, and water and nutrient holdingcapacity. One goal of soil quality research is to learn how to manage soil in a way that improvessoil function. Soils respond differently to management depending on the inherent properties ofthe soil and surrounding landscape.

Ecological definition of soil quality

“Defining and Assessing Soil Quality” (SSSA Special Pub. #35):- – The capacity of soil tofunction, within land use and ecosystem boundaries, to sustain biological (plant and animal)productivity, maintain (or enhance) environmental (water and air) quality, and promote plant,animal and human health”.

Soil Health

The soil health refers to self-regulation, stability, resilience, and lack of stress symptoms in a soilas an ecosystem. Soil health describes the biological integrity of the soil community-the balanceamong organisms within a soil and between soil organisms and their environment."

Soil Quality vs Soil Health • “The terms soil quality and soil health are often usedinterchangeably” (“Methods for Assessing Soil Quality),

but noted preferences:- – Producers prefer “soil health”, which portrays soil as a living,dynamic organism that functions holistically rather than an inanimate mixture of sand, silt andclay. • Characterized on the basis of descriptive and qualitative properties. – Soil scientists

prefer “soil quality”, which describes quantifiable physical, chemical and biologicalcharacteristics. • To scientists, soil “health” requires value judgements that cannot be

Soil Quality Indicators: Measures of Soil Functional State

Scientists use soil quality indicators to evaluate how well soil functions since soil function oftencannot be directly measured. Measuring soil quality is an exercise in identifying soil propertiesthat are responsive to management, affect or correlate with environmental outcomes, and arecapable of being precisely measured within certain technical and economic constraints. Soilquality indicators may be qualitative (e.g. drainage is fast) or quantitative (infiltration= 2.5 in/hr).

Ideal indicators should:

correlate well with ecosystem processes integrate soil physical, chemical, and biological properties & processes be accessible to many users be sensitive to management & climate be components of existing databases be interpretable

Difference in simplest form : Soil health is the status of soil , while soil quality is theservice , soil is providing towards the plant .

Table 3. Key soil indicators for soil quality assessment (after Arshad and Coen 1992, Doranand Parkin 1994,Gregorich et al. 1994, Larson and Pierce 1991, Carter et al. 1997, Karlen et al.1997, Martin et al. 1998)Selected indicator Rationale for selectionOrganic matter Defines soil fertility and soil structure, pesticide and waterretention, and use in process modelsTopsoil-depth Estimate rooting volume for crop production and erosionAggregation Soil structure, erosion resistance, crop emergence an earlyindicator of soil management effectTexture Retention and transport of water and chemicals, modeling useBulk density Plant root penetration, porosity, adjust analysis to volumetric basisInfiltration Runoff, leaching and erosion potentialpH Nutrient availability, pesticide absorption and mobility, process modelsEC Defines crop growth, soil structure, water infiltration; presently

lacking in most process modelsSuspected pollutants Plant quality, and human and animal healthSoil respiration Biological activity, process modeling; estimate of biomass activity,

early warning of management effect on organic matterForms of N Availability of crops, leaching potential, mineralization/ immobilization

rates, process modelingExtractable N, P and K Capacity to support plant growth, environmental quality indicator

Healthy Soil for Life

Soil health, also referred to as soil quality, is defined as the continued capacity of soil to functionas a vital living ecosystem that sustains plants, animals, and humans. This definition speaks tothe importance of managing soils so they are sustainable for future generations. To do this, weneed to remember that soil contains living organisms that when provided the basic necessitiesof life - food, shelter, and water - perform functions required to produce food and fiber.

The term soil health is used to describe the state of a soil in:

Sustaining plant and animal productivity and biodiversity (Soil biodiversity); Maintaining or enhance water and air quality; Supporting human health and habitation

Healthy soil gives us clean air and water, bountiful crops and forests, productive grazing lands,diverse wildlife, and beautiful landscapes. Soil does all this by performing five essentialfunctions:

Regulating water - Soil helps control where rain, snowmelt, and irrigation water goes.Water and dissolved solutes flow over the land or into and through the soil.

Sustaining plant and animal life - The diversity and productivity of living things dependson soil.

Filtering and buffering potential pollutants - The minerals and microbes in soil areresponsible for filtering, buffering, degrading, immobilizing, and detoxifying organic andinorganic materials, including industrial and municipal by-products and atmosphericdeposits.

Cycling nutrients - Carbon, nitrogen, phosphorus, and many other nutrients are stored,transformed, and cycled in the soil.

Physical stability and support - Soil structure provides a medium for plant roots. Soilsalso provide support for human structures and protection for archeological treasures.

Ecological functions of soil (FAO 1995) and their indicatorsEcological Functions of Soil Indicators of ProperFunctioningProduction function High levels of crop yields and incomesBiotic environmental function/living space function High levels of species richness andfunctional dominance of beneficial organisms – High levels of crop yields and

incomes and high quality food and habitationClimate-regulative function/storage function High levels of carbon stocks and slow

rates of greenhouse gas emissionsHydrologic function Adequate availability of water/reduced

risks floodsWaste and pollution control function High levels of crop yields and incomes

and high quality food and habitationArchive or heritage function Connective space function

Distribution of Waste land and problem soils in India.

WastelandWasteland Survey and Reclamation Committee, Ministry of food and Agriculture, govt, of India(1961) has defined wastelands as those lands which are either not available for cultivationor left out without being cultivated for some reason or other.Bhumla and Khare (1987) gives a working definition of wastelands. According to them“Those lands are wastelands (a) which are ecologicaly unstable, (b) whose top soilhas nearly been completely lost, and (c) which have developed toxicity inthe root zones or growth of most plants, both annual crops and trees”.Definition:Wastelands include degraded forests, overgrazed pastures, drought-struck pastures, erodedvalleys, hilly slopes, waterlogged marshy lands, barren land etc.As per this definition wastelands are classified into twocategories- culturable wastelands and unculturable wastelands.

1. The culturable category includes all possible wasteland areas which can bebrought under vegetation (though after adequate treatment).

2. On the other hand, unculturable wastelands are the lands which cannot bedeveloped for vegetative cover. In other words, land which is barren and cannotbe put to any productive use, such as agriculture, and forest cover is unculturablewasteland.

Six types of wastelands are found and these are described below:Gullied land/ravinous land

1. Gullied land- the gullies are the result of the localized surface runoff affecting the friableunconsolidated material resulting in the formation of perceptible channels resulting inundulating terrain having a maximum depth of 3m. They are the first stage of excessiveland dissection followed by their networking which leads to the develop ment of ravinousland. Ravinous land - this category of land contains system of gullies running more orless parallel lo each other in deep alluvium and entering a nearby river flowing muchlower than the surrounding table lands as are found along the courses of many rivers.

2. Undulating upland with or without scrubThis is the land of undulating nature prone to degradation. This may or may not havescrub cover. Such land occupies topographically high locations with 3° to 10° slope,often showing flat tops as in the case of standstones, laterite and basaltic plateau areaswith gentle tops and gentle to moderate slopes.

3. Surface waterlogged and marshy landThis is the land where water table is at /or near the surface and water stands for most ofthe year. Waterlogging occurs due to the rise of sub-soil water-table and this happensalmost all the over-irrigated areas. This problem is generally seen in the areas of canalirrigation where due to the seepage of water from canals, the sub-soil becomessaturated with water.Marsh is the land which permanently or periodically is inundated by water and ischaracterized by vegetation that includes grasses and reeds. Marshes are classified intosalt, brackish and fresh water categories depending on the salinity of water.

4. Shifting cultivation area Such land is the result of cyclic land use consisting of felling oftrees and burning of forest areas for growing crops. This results in extensive soil lossesleading to land degradation.

5. Degraded/under utilized notified forest land Lands as notified under the forest actand those lands with various types of forest cover in which denudation of vegetationcover is less than 20% of canopy cover, are classified as degraded land.

6. Degraded pastures/grazing land All those grazing lands in non-forest areas, whetheror not they are permanent pastures or meadows, which have become degraded due tolack of proper soil conservation and drainage measures fall under this category.

Wasteland status in India: Estimated Area under the wastelands provided by differentorganization

Source Area (m.ha.)Ministry of Agriculture and the JNU, Deptt. Of Geography (1986) 175National Land Use and Wasteland Development Council (First Meeting 1986) 123Society for Promotion of Wasteland Development (1982) 145Ministry of Rural Development & NRSA (2000) 64

State wise wastelands of India- NRSA (Information as on year 2003)State Wasteland (Area: In square km)Andhra Pradesh 45267.15Arunachal Pradesh 18175.95Assam 14034.08Bihar 5443.68Chhattisgarh 7584.15Goa 531.29Gujarat 20377.74Haryana 3266.45Himachal Pradesh 28336.80J & K 70201.99Jharkhand 11165.26Karnataka 13536.58Kerala 1788.80Madhya Pradesh 57134.03Maharashtra 49275.41Manipur 13174.74Meghalaya 3411.41Mizoram 4469.88Nagaland 3709.40Orissa 18952.74Punjab 1172.84Rajasthan 101453.86Sikkim 3808.21Tripura 1322.97Tamil Nadu 17303.29Uttarakhand 16097.46Uttar Pradesh 16984.16West Bengal 4397.56Union Territory 314.38Total 552692.26

Total geographical area of India: 3287263 sq. km

The main causes of formation of wastelands are:(a) Indiscriminate and over utilisation of forest produces

(b) Over-grazing

(c) Side effects of development projects

(d) Mis-use and unscientific land management.

Causes of Land DegradationCauses of Degradation Area (million hectares) Percentage of total areaWater erosion 107.12 61.7Wind erosion 17.79 10.24Ravines 3.97 2.28Salt-affected 7.61 4.38Waterlogging 8.52 4.90Mines & quarry wastes - -Degraded land due to shifting cultivation 4.91 2.82Degraded forest lands 19.49 11.22Special problems 2.73 1.57Coastal sandy areas 1.46 0.84TOTAL 173.64 100.0Source : Ministry of Agriculture, Government of India (1985)

A list of Pedotransfer Functions: Mathematical functions that relates soil characteristics andproperties with one another for evaluation of soil quality

1. CEC2. Phosphate sorption capacity3. Change in organic matter4. B.D.5. Water retention6. Porosity increases7. Hydraulic conductivity8. Soil Productivity

Extent and distribution of salt affected soils in India

Sr. No. State Saline soils(ha)

Alkalisoils(ha)

Coastal salinesoil(ha)

Total(ha)

1 Andhra Pradesh 0 196609 77598 2742072 A & N islands 0 0 77000 770003 Bihar 47301 105852 0 1531534 Gujarat 1218255 541430 462315 22220005 Haryana 49157 183399 0 2325566 J & K* 0 17500 0 175007 Karnataka 1307 148136 586 1500298 Kerala 0 0 20000 200009 Maharashtra 177093 422670 6996 60675910 Madhya Pradesh 0 139720 0 139720

11 Orissa 0 0 147138 14713812 Punjab 0 151717 0 15171713 Rajasthan 195571 179371 0 37494214 Tamil Nadu 0 354784 13231 36801515 Uttar Pradesh 21989 1346971 0 136896016 West Bengal 0 0 441272 441272

Total 1710673 3788159 1246136 6744968

Table 2 Major soil groups in IndiaSoils Area (Mha)Red and laterite soils 117.2Black soils 73.5Alluvial soils 58.4Desert soils 30.0Other soils {saline–alkali soils, forest and hill soils, peaty and marshy soils} 49.6

Salt-affected soils occur at a tune of 6.73 Mha in our country.

Problem SoilsThe soils which possess characteristics that make them uneconomical for the cultivation ofcrops without adopting proper reclamation measures are known as problem soils.

Types of problem soils1. Physical problem soils2. Chemical Problem soils3. Biological Problem soils4. Nutritional problem soils as a result of above constraints

Soils with Physical problems1.1. Slow permeable soils/Impermeable soils and their managementOccurrence and CausesIn Tamil Nadu, the area under slow permeable soils is around 7,54,631 ha (7.5% of TGA). Slowpermeable soil is mainly due to very high clay content, infiltration rate < 6cm/day, so more runoffwhich eventually leads to soil erosion and nutrient removal. Since the capillary porosity is high itleads to impeded drainage, poor aeration and reduced conditions.

Remedial measures(i) Incorporation of organics: Addition of organics namely FYM/composted coir pith/press mud at12.5 t ha-1 found to be optimum for the improvement of the physical properties(ii) Formation of ridges and furrows: For rainfed crops, ridges are formed along the slopes forproviding adequate aeration to the root zone.iii) Formation of broad beds: To reduce the amount of water retained in black clay soils duringfirst 8 days of rainfall, broad beds of 3-9 m vide should be formed either along the slope oracross the slope with drainage furrows in between broad beds.iv). providing open/ subsurface drainagev). Huge quantity of sand /red soil application to change the texturevi). Contour /compartmental bunding to increase the infiltrationvii). Application of soil conditioners like vermiculite to reduce runoff and erosion

1.2. Soil surface crustingOccurrence and CausesIn Tamil Nadu, surface crusting is prevalent in Trichy, Thanjavur, Pudukottai, Cuddalore andSivaganga districts and mostly in red soil areas. In Tamil Nadu, the area under soil crusting isaround 4,51,584 ha ( 4.49% TGA). Surface crusting is due to the presence of colloidal oxides ofiron and aluminium in soils which binds the soil particles under wet regimes. On drying it forms ahard mass on the surface. It is predominant in Alfisols but also occur in other soils too. (Fig : 4)Impact on soil propertiesPrevent germination of seeds and retards root growthResults in poor infiltration and accelerates surface runoffCreates poor aeration in the rhizosphereAffects nodule formation in leguminous cropsRemedial measuresWhen the soil is at optimum moisture regime, ploughing is to be done.Lime or gypsum @ 2 t ha-1 may be uniformly spread and another ploughing given for blendingof amendment with the surface soil.Farm yard manure or composted coir pith @ 12.5 t ha-1 or other organics may be applied toimprove the physical properties of the soils

Scraping the surface soil by tooth harrow will be useful.Bold grained seeds may be used for sowing on the crusted soils.More number of seeds/hill may be adopted for small seeded crops.Sprinkling water at periodical intervals may be done wherever possible.Resistant crops like cowpea can be grown.1.3. Sub soil hard panOccurrence and CausesSub soil hard pan is commonly found in red soils. Though soil is fertile, crops cannot absorbnutrients from the soil which leads to reduction in crop yields. In Tamil Nadu, it is prevalent inCoimbatore, Erode, Dharmapuri, Trichy, Cuddalore, Villupuram, Pudukottai, Sivagangai,Madurai and Salem districts particularly under rainfed conditions. In Tamil Nadu, the area undersubsoil hardpan is around 10, 54,661 ha (10.48% TGA) The reasons for the formation of subsurface hard pan in red soils is due to the illuviation of clay to the sub soil horizons coupled withcementing action of oxides of iron, aluminium and calcium carbonate.

Impact on soil physical propertiesThe sub soil hard pan is characterized by high bulk density(>1.8 Mg m-3) which in turn lowersinfiltration, water holding capacity, available water and movement of air and nutrients withconcomitant effect on the yield of crops.Chiselling technology to overcome the sub soil hard panThe field is to be ploughed with chisel plough, a tractor drawn heavy iron plough at 50 cminterval in both the directions. Chiselling helps to break the hard pan in the sub soil besides itploughs up to 45 cm depth. Farm yard manure or press mud or composted coir pith at 12.5 t ha-1 is to be spread evenly on the surface. The field should be ploughed with country plough twicefor incorporating the added manures. The broken hard pan and incorporation of manures makethe soil to conserve more moisture.1.4. Shallow soilsOccurrence and CausesIn Tamil Nadu, shallow soils occur over an area of around 1,16,509 ha ( 1.16.% TGA). Shallowsoils are formed due to the presence of parent rocks immediately below the soil surface ( 15-20cm depth).Impact

The shallow soil restricts root elongation and spreading. Due to shallowness less volume of soilis available exhaustive soil nutrients.Management

Growing shallow rooted crops.

Frequent renewal of soil fertility

Growing crops that can withstand shallowness (Mango, country goose berry, fig,tamarind, ber and cashew etc)

1.5. Highly permeable soilsOccurrence and CausesSandy soils containing more than 70 per cent sand fractions occur in coastal areas, river deltaand in the desert belts. Such soils occur in Coimbatore, Trichy, Kanyakumari, Tuticorin,Thanjavur and Tirunelveli districts and in part of coastal areas in Tamil Nadu. A total area of24,12,086 ha in Tamil Nadu are affected by excessively permeable soilsImpactExcessive permeability of the sandy soils results in poor water retention capacity, very highhydraulic conductivity and infiltration rates. These soils being devoid of finer particles andorganic matter, the aggregates are weakly formed, the non-capillary pores dominating with verypoor soil structure. So whatever the nutrients and water added to these soils are not utilized bythe crops and subjected to loss of nutrients and water. In addition, it is not providing anchorageto the crops grown.Management technologyThe soils should be ploughed uniformly. Twenty four hours after a good rainfall or irrigation, thesoil should be rolled 10 times with 400 kg stone roller of 1 m long or an empty tar drum filledwith 400 kg sand at optimum moisture (13 %). Then shallow ploughing should be given andcrops can be raised. Application of clay soil up to a level 100 t ha-1 based on the severity of theproblem and availability of clay materials. Application of organic materials like farm yardmanure, compost, press mud, sugar factory slurry, composted coir pith, sewage sludge etc.Providing asphalt sheet, polythene sheets etc. below the soil surface to reduce the infiltrationrate. Crop rotation with green manure crops like Sunhemp, sesbania, daincha, kolinchi etc.Frequent irrigation with low quantity of water. Frequent split application of fertilizers and slowrelease fertilizers like neem coated urea1.6. Heavy clay soilsClay soils are referred as heavy soils. To be classified as clay soil, it should be made up ofabout 40% clay particles, the finest particles found in soil.This is also slowly permeable soils.Main production constraintsHeavy have very hard consistence when dry and very plastic and sticky ("heavy") when wet.Therefore the workability of the soil is often limited to very short periods of medium (optimal)water status. However, tillage operations can be performed in the dry season with heavymachinery. Mechanical tillage in the wet season causes serious soil compaction.They are imperfectly to poorly drained, leaching of soluble weathering products is limited.This is due to the very low hydraulic conductivity. Once the soil has reached its fieldcapacity, practically no water movement occurs. Flooding can be a major problem inareas with higher rainfall. Surface water may be drained by open drains.Most of the heavy clay soils belonging to Vertisols are chemically rich and are capableof sustaining continuous cropping. They do not necessarily require a rest period for

recovery; because the pedoturbation continuously brings subsoil to the surface.However, the overall productivity normally remains low, especially where no irrigation water isavailable. Nitrogen is normally deficient as well as phosphorus. Potassium contents arevariable. Secondary elements and micronutrients are often deficient. In semi-arid areas freecarbonate and gypsum accumulations are common.There are two broad groups of vertisolsSelf-mulching Vertisols. These have a fine (granular or crumb) surface soil structureduring thedry season. When such soils are ploughed, the clods, after being subjected to repeat wettingand drying, disintegrate. Crusty Vertisols. These have a thin, hard crust in the dry season. Whenploughed, crusty Vertisols produce large, hard clods that may persist for 2 to 3 years beforethey have crumbled enough to permit the preparation of a good seedbed. Such soils requiremechanical tillage if they are to be cultivated.The structural stability of high clay soils remains low. They are therefore very susceptible towater erosion. Slopes above 5 per cent should not be used for arable cropping, and on gentlerslopes contour cultivation with a groundcover crop is advisable. When terracing, sufficientsurface drainage must be provided. The strategies suggested for slowly permeable soils alsohold good for clay soil.1.7. Fluffy paddy soilsOccurrence and CausesIn Tamil Nadu, fluffy paddy soils are prevalent in Cauvery delta zone and in many parts of thestate. It is formed due to the continuous rice-rice cropping sequence. In Tamil Nadu about25,919 ha of land is affected by fluffiness (0.26 % of TGA).The traditional method of preparing the soil for transplanting rice consists of puddling whichresults in substantial break down of soil aggregates into a uniform structure less mass. The solidand liquid phases of the soil are thus changed. Under continuous flooding and submergence ofthe soil for rice cultivation in a cropping sequence of rice-rice-rice, as in many parts of TamilNadu, the soil particles are always in a state of flux and the mechanical strength is lost leadingto the fluffiness of the soils. This is further aggravated by in situ incorporation of rice stubblesand weeds during puddling.Impact of fluffinessSinking of draught animals and labourers is one of the problems during puddling in rice fieldswhich is an invisible drain of finance for the farmers due to high pulling power needed for thebullocks and slow movement of labourers during the puddling operations. Further, it leads to lowbulk density and very rapid hydraulic conductivity which in turn affects anchorage to the rootsand the potential yield of crops is adversely affected.Management Methodology

Irrigation should be stopped 10 days before the harvest of rice crop

After the harvest of rice, when the soil is under semi-dry condition proctor moisture level,compact the field by passing 400 kg stone roller or an empty tar drum filled with 400 kgsand 8 times.

Usual preparatory cultivation is carried out after compaction.

Problem soils and their management

"The multiple roles of soils often go unnoticed. Soils don’t have a voice, and few people speak out for them. They

are our silent ally in food production."

Jose Graziano da Silva, FAO Director-General

Soil is a natural finite resource base which sustains life on earth. It is a three phase dynamic system that performs

many functions and ecosystem services and highly heterogeneous. Soil biota is the biological universe which helps the soil

in carrying out its functions. Often soil health is considered independently without referring to interlinked soil functions

and also based on soil test for few parameters. Physical condition of soil and biological fertility are overlooked in soil

health management which needs revisiting of soil users. Recognising the importance of soil health in all dimensions, 2015

has been declared as the International Year of Soils by the 68th UN General Assembly. Food and Agriculture organisation

of the United Nations has formed Global soil partnership with various countries to promote healthy soils for a healthy life

and world without hunger. India, the second most populous country in the world faces severe problems in agriculture. It is

estimated that out of the 328.8 m ha of the total geographical area in India, 173.65 m ha are degraded, producing less than

20% of its potential yield (Govt. of India, 1990).

Soil heterogeneity is the reasons for the diverse nature of cropping and production pattern. Soil heterogeneity is the case

where soil in a relatively small area varies greatly in texture, fertility, topography, moisture content, drainage etc. If it

exists in large scale due to the parent material or manmade activities, then the problem of soil suitability to agriculture

arises.

Soil consists of a solid phase (minerals and organic matter) as well as a porous phase that holds gases and water.

Accordingly, soils are often treated as a three-state system as shown in fig 1. From an agriculture point, the soil should

support all the functions as in fig 2

The soils which possess characteristics that make them uneconomical for the cultivation of crops without adopting

proper reclamation measures are known as problem soils.

Often we resort to chemical means of reclamation that leads to impairment of ecosystem functions. Resorting to naturalmeans and integrated methods will resolve the issue and prevent causing irreparable damage

Types of problem soils

Physical problem soils

Chemical Problem soils

Biological Problem soils

Nutritional problem soils as a result of above constraints

1. Soils with Physical problems

1.1. Slow permeable soils/Impermeable soils and their management

Occurrence and Causes

In Tamil Nadu, the area under slow permeable soils is around 7,54,631 ha (7.5% of TGA). Slow permeable soil is

mainly due to very high clay content, infiltration rate < 6cm/day, so more runoff which eventually leads to soil erosion and

nutrient removal. Since the capillary porosity is high it leads to impeded drainage, poor aeration and reduced conditions.

Remedial measures

(i)Incorporation of organics: Addition of organics namely FYM/composted coir pith/press mud at 12.5 t ha-1 found to be

optimum for the improvement of the physical properties

(ii)Formation of ridges and furrows: For rainfed crops, ridges are formed along the slopes for providing adequate aeration

to the root zone.

iii)Formation of broad beds: To reduce the amount of water retained in

black clay soils during first 8 days of rainfall, broad beds of 3-9 m vide should be formed either along the slope or acrossthe slope with drainage furrows in between broad beds.

iv). providing open/ subsurface drainage

v). Huge quantity of sand /red soil application to change the texture vi). Contour /compartmental bunding to increase the

infiltration

vii). Application of soil conditioners like vermiculite to reduce runoff and erosion

1.2. Soil surface crusting


In Tamil Nadu, surface crusting is prevalent in Trichy, Thanjavur, Pudukottai, Cuddalore and Sivaganga districts

and mostly in red soil areas. In Tamil Nadu, the area under soil crusting is around 4,51,584 ha ( 4.49% TGA). Surface

crusting is due to the presence of colloidal oxides of iron and aluminium in soils which binds the soil particles under wet

regimes. On drying it forms a hard mass on the surface. It is predominant in Alfisols but also occur in other soils too.

Impact on soil properties

Prevent germination of seeds and retards root growth Results in poor infiltration and accelerates surface runoff Creates

poor aeration in the rhizosphere

Affects nodule formation in leguminous crops

Remedial measures

When the soil is at optimum moisture regime, ploughing is to be done. Lime or gypsum @ 2 t ha-1 may be uniformly

spread and another ploughing given for blending of amendment with the surface soil.

Farm yard manure or composted coir pith @ 12.5 t ha-1 or other organics may be applied to improve the physical

properties of the soils Scraping the surface soil by tooth harrow will be useful.

Bold grained seeds may be used for sowing on the crusted soils. More number of seeds/hill may be adopted for small

seeded crops. Sprinkling water at periodical intervals may be done wherever

possible.

Resistant crops like cowpea can be grown.

1.3. Sub soil hard pan


Sub soil hard pan is commonly found in red soils. Though soil is fertile, crops cannot absorb nutrients from the soil

which leads to reduction in crop yields. In Tamil Nadu, it is prevalent in Coimbatore, Erode, Dharmapuri, Trichy,

Cuddalore, Villupuram, Pudukottai, Sivagangai, Madurai and Salem districts particularly under rainfed conditions. In

Tamil Nadu, the area under subsoil hardpan is around 10, 54,661 ha (10.48% TGA) The reasons for the formation of sub

surface hard pan in red soils is due to the illuviation of clay to the sub soil horizons coupled with cementing action of

oxides of iron, aluminium and calcium carbonate.

Impact on soil physical properties

The sub soil hard pan is characterized by high bulk density(>1.8 Mg m-3) which in turn lowers infiltration, water

holding capacity, available water and movement of air and nutrients with concomitant effect on the yield of crops.Chiselling technology to overcome the sub soil hard pan

The field is to be ploughed with chisel plough, a tractor drawn heavy iron plough at 50 cm interval in both the

directions. Chiselling helps to break the hard pan in the sub soil besides it ploughs up to 45 cm depth. Farm yard manure

or press mud or composted coir pith at 12.5 t ha-1 is to be spread evenly on the surface. The field should be ploughed with

country plough twice for incorporating the added manures. The broken hard pan and incorporation of manures make the

soil to conserve more moisture.

1.4. Shallow soils


In Tamil Nadu, shallow soils occur over an area of around 1,16,509 ha ( 1.16.% TGA). Shallow soils are formed

due to the presence of parent rocks immediately below the soil surface ( 15-20 cm depth).

Impact

The shallow soil restricts root elongation and spreading. Due to shallowness less volume of soil is available

exhaustive soil nutrients.

Management

Growing shallow rooted crops. Frequent renewal of soil fertility

Growing crops that can withstand shallowness(Mango, country goose berry, fig, tamarind, ber and cashew etc)

1.5. Highly permeable soils


Sandy soils containing more than 70 per cent sand fractions occur in coastal areas, river delta and in the desert

belts. Such soils occur in Coimbatore, Trichy, Kanyakumari, Tuticorin, Thanjavur and Tirunelveli districts and in part of

coastal areas in Tamil Nadu. A total area of 24,12,086 ha in Tamil Nadu are affected by excessively permeable soils

Impact

Excessive permeability of the sandy soils results in poor water retention capacity, very high hydraulic conductivity

and infiltration rates. These soils being devoid of finer particles and organic matter, the aggregates are weakly formed,

the non-capillary pores dominating with very poor soil structure. So whatever the nutrients and water added to these soils

are not utilized by the crops and subjected to loss of nutrients and water. In addition, it is not providing anchorage to the

crops grown.

Management technology

The soils should be ploughed uniformly.

Twenty four hours after a good rainfall or irrigation, the soil should be rolled 10 times with 400 kg stone roller of 1 m

long or an empty tar drum filled with 400 kg sand at optimum moisture (13 %)

Then shallow ploughing should be given and crops can be raised. Application of clay soil up to a level 100 t ha-1 based on

the severity of the problem and availability of clay materials

Application of organic materials like farm yard manure, compost, press mud, sugar factory slurry, composted coir pith,

sewage sludge etc

Providing asphalt sheet, polythene sheets etc. below the soil surface to reduce the infiltration rate

Crop rotation with green manure crops like Sunhemp, sesbania, daincha, kolinchi etc

Frequent irrigation with low quantity of water

Frequent split application of fertilizers and slow release fertilizers like neem coated urea

1.6. Heavy clay soils

Clay soils are referred as heavy soils. To be classified as clay soil, it should be made up of about 40% clay

particles, the finest particles found in soil.This is also slowly permeable soils.

Main production constraints

Heavy have very hard consistence when dry and very plastic and sticky ("heavy") when wet. Therefore the

workability of the soil is often limited to very short periods of medium (optimal) water status. However, tillage operations

can be performed in the dry season with heavy machinery. Mechanical tillage in the wet season causes serious soil

compaction.

They are imperfectly to poorly drained, leaching of soluble weathering products is limited. This is due to the very

low hydraulic conductivity. Once the soil has reached its field capacity, practically no water movement occurs. Flooding

can be a major problem in areas with higher rainfall. Surface water may be drained by open drains.

Most of the heavy clay soils belonging to Vertisols are chemically rich and are capable of sustaining continuous

cropping. They do not necessarily require a rest period for recovery; because the pedoturbation continuously brings subsoil

to the surface. However, the overall productivity normally remains low, especially where no irrigation water is available.

Nitrogen is normally deficient as well as phosphorus. Potassium contents are variable. Secondary elements and

micronutrients are often deficient. In semi-arid areas free carbonate and gypsum accumulations are common.

There are two broad groups of vertisols

Self-mulching Vertisols. These have a fine (granular or crumb) surface soil structureduring the dry season. When

such soils are ploughed, the clods, after being subjected to repeat wetting and drying, disintegrate. Crusty Vertisols. These

have a thin, hard crust in the dry season. When ploughed, crusty Vertisols produce large, hard clods that may persist for 2

to 3 years before they have crumbled enough to permit the preparation of a good seedbed. Such soils require mechanical

tillage if they are to be cultivated.

The structural stability of high clay soils remains low. They are therefore very susceptible to water erosion. Slopes

above 5 per cent should not be used for arable cropping, and on gentler slopes contour cultivation with a groundcover crop

is advisable. When terracing, sufficient surface drainage must be provided. The strategies suggested for slowly permeable

soils also hold good for clay soil.

1.7. Fluffy paddy soils


In Tamil Nadu, fluffy paddy soils are prevalent in Cauvery delta zone and in many parts of the state. It is formed

due to the continuous rice-rice cropping sequence. In Tamil Nadu about 25,919 ha of land is affected by fluffiness (0.26 %

of TGA).

The traditional method of preparing the soil for transplanting rice consists of puddling which results in substantial

break down of soil aggregates into a uniform structure less mass. The solid and liquid phases of the soil are thus changed.

Under continuous flooding and submergence of the soil for rice cultivation in a cropping sequence of rice-rice-rice, as in

many parts of Tamil Nadu, the soil particles are always in a state of flux and the mechanical strength is lost leading to the

fluffiness of the soils. This is further aggravated by in situ incorporation of rice stubbles and weeds during puddling.

Impact of fluffiness

Sinking of draught animals and labourers is one of the problems during puddling in rice fields which is an invisible

drain of finance for the farmers due to high pulling power needed for the bullocks and slow movement of labourers during

the puddling operations. Further, it leads to low bulk density and very rapid hydraulic conductivity which in turn affects

anchorage to the roots and the potential yield of crops is adversely affected.

Management Methodology

∙Irrigation should be stopped 10 days before the harvest of rice crop

∙After the harvest of rice, when the soil is under semi-dry condition proctor moisture level, compact the field by

passing 400 kg stone roller or an empty tar drum filled with 400 kg sand 8 times. ∙Usual preparatory cultivation is carried out after compaction.

2.Chemical Problem soils

2.1.Salt - affected soils

The salt-affected soils occur in the arid and semiarid regions where evapo-transpiration greatly exceeds

precipitation. The accumulated ions causing salinity or alkalinity include sodium, potassium, magnesium, calcium,

chlorides, carbonates and bicarbonates. The salt- affected soils can be primarily classified as saline soil and sodic soil.

The state-wise distribution of salt affected soils in India is presented in the following table.

Saline soils

Saline soils defined as soils having a conductivity of the saturation extract greater than 4 dS m-1 and an

exchangeable sodium percentage less than 15 Saline soils defined as soils having a conductivity of the saturation extract

greater than 4 dS m-1 and an exchangeable sodium percentage less than 15. The pH is usually less than 8.5. Formerly these

soils were called white alkali soils because of surface crust of white salts.

67

Formation

The process by which the saline soil formed is called Salinization. Saline soils occur mostly in arid or semi arid

regions. In arid regions saline soils occur not only because there is less rainfall available

to leach and transport the salts but also because of high evaporation rates, which tend further to concentrate the salts in

soils and in surface waters

Major production constraints

Presence of salts leads to alteration of osmotic potential of the soil solution. Consequently water intake by plants

restricted and thereby nutrients uptake by plants are also reduced. In this soil due to high salt levels microbial activity is

reduced. Specific ion effects on plants are also seen due to toxicity of ions like chloride, sulphate, etc.

Management of saline soils

The reclamation of saline soils involves basically the removal of salts from the saline soil through the processes of

leaching with water and drainage. Provision of lateral and main drainage channels of 60 cm deep and 45 cm wide and

leaching of salts could reclaim the soils. Sub-surface drainage is an effective tool for lowering the water table, removal of

excess salts and prevention of secondary salinisation. of ions like chloride, sulphate, etc.

Management of saline soils

The reclamation of saline soils involves basically the removal of salts from the saline soil through the processes of

leaching with water and drainage. Provision of lateral and main drainage channels of 60 cm deep and 45 cm wide and leaching of

salts could reclaim the soils. Sub-surface drainage is an effective tool for lowering the water table, removal of excess salts and

prevention of secondary salinisation.Irrigation management

Proportional mixing of good quality (if available) water with saline water and then using for irrigation reduces the

effect of salinity. Alternate furrow irrigation favours growth of plant than flooding. Drip, sprinkler and pitcher irrigation

have been found to be more efficient than the conventional flood irrigation method since relatively lesser amount of water

is used under these improved methods.

Fertilizer management

Addition of extra dose of nitrogen to the tune of 20-25% of recommended level will compensate the low

availability of N in these soils. Addition of organic manures like, FYM, compost, etc helps in reducing the ill effect of

salinity due to release of organic acids produced during decomposition. Green manuring (Sunhemp, Daincha, Kolingi) and

or green leaf manuring also counteracts the effects of salinity.

Crop choice / Crop management

Crops are to be chosen based on the soil salinity level. The relative salt tolerance of different crops is as follows:

Relative tolerance of crops to salinity

Threshold PlantThreshold

Plantspecies

Salinity(dS m-1)

salinity (dS m-1) species

Field cropsVegetables

Cotton 7.7 Tomato 2.5

Sugarbeet 7.0 Cabbage 1.8

Sorghum 6.8 Potato 1.7

Wheat 6.0 Onion 1.2

Soybean 5.0 Carrot 1.0

Groundnut 3.2Fruits

Rice 3.0 Citrus 1.7

Maize 1.7- -

Sugarcane 1.7- -

Soil / cultural management

Planting the seed in the centre of the raised bed / ridge may affect the germination as it is the spot of greatest salt

accumulation. A better salinity control can be achieved by using sloping beds with seeds planted on the sloping side just

above the water line. Alternate furrow irrigation is advantageous as the salts can be displaced beyond the single seed row.

Application of straw mulch had been found to curtail the evaporation from soil surface resulting in the reduced salt

concentration in the root zone profile within 30 days.

2.2. Alkali / Sodic soils

Alkali or sodic soil is defined as a soil having a conductivity of the saturation extract less than 4 dS m-1 and an

exchangeable sodium percentage greater than 15. The pH is usually between 8.5 – 10.0. Most alkali soils, particularly in

the arid and semi-arid regions, contain CaCO3 in the profile in some form and constant hydrolysis of CaCO3 sustains the

release of OH- ions in soil solution. The OH- ions so released result in the maintenance of higher pH in calcareous alkali

soils than that in non – calcareous alkali soils.

Expected loss of soil productivity due to ESP in different soils

ESP Loss in productivity (%)

Alluvium derived soils Black soils

(Inceptisols / Alfisols) (Vertisols)

Up to 5 Nil Up to 10

5-15 <10 10-25

15-40 10-25 25-50

>40 25-50 >50

Formation

Soil colloids adsorb and retain cations on their surfaces. Cation adsorption occurs as a consequence of the electrical

charges at the surface of the soil colloids. While adsorbed cations are combined chemically with the soil colloids, they

may be replaced by other cations that occur in the soil the soil colloids. While adsorbed cations are combined chemically

with the soil colloids, they may be replaced by other cations that occur in the soil solution. Calcium and magnesium are

the principal cations found in the soil solution and on the exchange complex of normal soils in arid regions. When excess

soluble salts accumulate in these soils, sodium frequently becomes the dominant cation in the soil solution resulting alkali

or sodic soils.

Ca2+

Major production constraints

Excess exchangeable sodium in alkali soils affects both the physical and chemical properties of soils.

a)Dispersion of soil colloids

b)Specific ion effect

Reclamation of alkali / sodic soils

Physical Amelioration

This is not actually removes sodium from exchange complex but improve physical condition of soil through improvementin infiltration and aeration. The commonly followed physical methods include

Deep ploughing is adopted to break the hard pan developed at subsurface due to sodium and improving free-movement water.

This also helps in improvement of aeration.

Providing drainage is also practiced to improve aeration and to remove further accumulation of salts at root zone.

Sand filling which reduces heaviness of the soil and increases capillary movements of water.

Profile inversion – Inverting the soil benefits in improvement of physical condition of soil as that of deep ploughing.

Chemical Amelioration

Reclamation of alkali / sodic soils requires neutralization of alkalinity and replacement of most of the sodium ions

from the soil – exchange complex by the more favourable calcium ions. This can be accomplished by the application of

chemical amendments (the materials that directly or indirectly furnish or mobilize divalent cations, usually

for the replacement of sodium from the exchange complex of the soil) followed by leaching to remove soluble salts andother reaction products. The chemical amendments can be broadly grouped as follows:

Direct Ca suppliers: Gypsum, calcium carbonate, phospho-gypsum, etc.

Indirect Ca suppliers: Elemental Sulphur, sulphuric acid, pyrites, FeSO4, etc

Among them gypsum is, by far, the most commonly used chemical amendment. Calcium carbonate is insoluble in

nature which of no use in calcareous sodic soils (have already precipitated CaCO3) but can be used in non calcareoussodic

soils (do not have precipitated CaCO3) since pH of this soils are low at surface and favouring solubilisation of CaCO3.

Some of indirect suppliers of Ca viz. Elemental sulphur, sulphuric acid, iron sulphate are also used for calcareous sodic

soils. These materials on application solubilise the precipitated CaCO3 in sodic soils and releases Ca for reclamation.

Other sources

Distillery spent wash

Distillery spent wash is acidic (pH 3.8-4.2) with considerable quantity of magnesium. About 2 lakh litres of distillery

spent wash can be added to an acre of sodic soil in summer months. Natural oxidation is induced for a period of six weeks

with intermittent ploughing once in a month. In the second month (after 45-60 days) fresh water may be irrigated and

drained. Such a treatment reduces the pH and exchangeable sodium percentage

Distillery effluent

Distillery effluent contains macro and micronutrients. Because of its high salt content, it can be used for one time

application to fallow lands, About 20 to 40 tonnes per ha of distillery effluent can be sprayed uniformly on the fallow land.

It should not be allowed for complete drying over a period of 20 to 30 days. The effluent applied field has to be thoroughly

ploughed two times for the oxidation and mineralization of organic matter. Then the crops can be cultivated in the effluent

applied fields by conventional methods.

Pulp and paper mill effluents

Pulp and paper effluents contain lot of dissolved solids and stabilized organic matter and if properly treated can

safely be used for irrigation with amendments viz. pressmud @ 5 tonnes ha-1, fortified pressmud @ 2.5 tonne ha-1 or

daincha as in situ green manure.

Crop choice

Rice is preferred crop in alkali / sodic soil as it can grow under submergence, can tolerate fair extent of ESP and

can influence several microbial processes in the soil. Agroforestry systems like silviculture, silvipasture etc. can improve

the physical and chemical properties of the soil along with additional return on long-term basis. Some grasses

like Brachariamutica (Para grass) and Cynodondactylon (Bermuda grass) etc. has been reported to produce 50% yield at

ESP level above 30.

The sodicity tolerance ratings of different crops is given in table.

Relative tolerance of crops to sodicity

ESP (range*) Crop

2-10 Deciduous fruits, nuts, citrus, avocado

10-15 Safflower, black gram, peas, lentil, pigeon pea

16-20 Chickpea, soybean

20-25 Clover, groundnut, cowpea, pearl millet

25-30 Linseed, garlic, cluster bean

30-50 Oats, mustard, cotton, wheat, tomatoes

50-60 Beets, barley, sesbania

60-70 Rice

*Relative yields are only 50% of the potential in respective sodicity ranges.

Relative tolerance of fruit trees to sodicityTolerance to sodicity ESP Trees

High 40-50 Ber, tamarind, sapota, wood apple,

date palm

Medium 30-40 Pomegranate

Low 20-30 Guava, lemon, grape

Sensitive 20 Mango, jack fruit, banana

2.3. Saline-alkali/ sodic soils

Saline-alkali / sodic soil is defined as a soil having a conductivity of the saturation extract greater than 4 dS m-1 and

an exchangeable sodium percentage greater than 15. The pH is variable and usually above 8.5depending on the relative

amounts of exchangeable sodium and soluble salts. When soils dominated by exchangeable sodium, the pH will be more

than 8.5 and when soils dominated by soluble salts, the pH will be less than 8.5.

Formation

These soils form as a result of the combined processes of salinisation and alkalization. If the excess soluble salts of

these soils are leached downward, the properties of these soils may change markedly and become similar to those of sodic

soil.

Management of saline alkali soils

The reclamation / management practices recommended for the reclamation of sodic soil can be followed for the

management of saline – sodic soil.

2.4. Acid soils

Soil acidity refers to presence of higher concentration of H+ in soil solution and at exchange sites. They are

characterized by low soil pH and with low base saturation. The ranges in soil pH and associated degree of acidity are as

follows:

pH range Nature of acidity

3-4 Very strong

4-5 Strong

5-6 Moderate

6-7 Slight

In acid soil regions (ASR) precipitation exceeds the evapo- transpiration and hence leaching is predominant

causing loss of bases from the soil. When the process of weathering is drastic, the subsoil and in many cases, the whole

profile becomes acidic.

Occurrence

Acid soils occupy approximately 60% of the earth land area and are arise under humid climate conditions from

carbonaceous less soil forming rocks in all thermal belts of the earth.

• World wide – 800 M ha

• India - 100 M ha

• Tamil Nadu - 2.6 M ha (20% of GA)

95% of soils of Assam and 30% of geographical area of Jammu and Kashmir are acidic. In West Bengal, 2.2 M ha, in

Himachal Pradesh, 0.33 M ha, in Bihar, 2 Mha and all hill soils of erstwhile Uttar Pradesh come under acid soils. About

80% of soils in Orissa, 88% in Kerala, 45% in Karnataka and 20% in Maharastra are acidic. The laterite zone in Tamil

Nadu is covered with acid soil and about 40,000 ha are acidic in Andhra Pradesh.

Sources of soil acidity

Leaching due to heavy rainfall

Acidic parent material and alumina silicate minerals

Acid forming fertilizers

Humus and other organic acids

Carbon dioxide and hydrous oxides

Acid rain

Production constraints

Increased solubility and toxicity of Al, Mn and Fe

Deficiency of Ca and Mg,

Reduced availability of P and Mo and

Reduced microbial activity

Management of acid soils

Management of the acid soils should be directed towards enhanced crop productivity either through addition of

amendments to correct the soil abnormalities or by manipulating the agronomic practices depending upon the climatic and

edaphic conditions.

Soil amelioration

Lime has been recognized as an effective soil ameliorant as it reduces Al, Fe and Mn toxicity and increases base

saturation, P and Mo availability of acid soils. Liming also increases atmospheric N fixation as well as N mineralization in

acid soils through enhanced microbial activity. However, economic feasibility of liming needs to be worked out before

making any recommendation.

Liming materials

Commercial limestone and dolomite limestone are the most widely used amendments. Carbonates, oxides and hydroxides

of calcium and magnesium are referred to as agricultural lime. Among, the naturally occurring lime sources calcitic, dolomitic

and stromato litic limestones are important carbonates.

The other liming sources are marl, oyster shells and several industrial wastes like steel mill slag, blast furnace slag, lime

sludge from paper mills, pressmud from sugar mills, cement wastes, precipitated calcium carbonate, etc equally effective as

ground limestone and are also cheaper. Considering the efficiency of limestone as 100%, efficiencies of basic slag and dolomite

are 110 and 94 % respectively. Basic slag and pressmud are superior to calcium oxide or carbonates for amending the acid soils.

Fly ash, a low- density amorphous ferro-alumino silicate, also improves pH and nutrient availability.

Lime requirement of an acid soil may be defined as the amount of liming material that must be added to raise the

pH to prescribed value. Shoemaker et al. (1961) buffer method is used for the determination of lime requirement of an acid

soil.

Crop choice

Selection of crops tolerant to acidity is an effective tool to counter this soil problem and breeding of such varieties

is of specific importance for attaining higher productivity, particularly in areas where liming is not an economic

proposition. The crops can be grouped on the basis of their performance in different soil pH range.

Relative tolerance of crops to soil acidity

CropsOptimum pHrange

Cereals

Maize, sorghum, wheat, barley 6.0-7.5

Millets 5.0-6.5

Rice 4.0-6.0

Oats 5.0-7.7

Legumes

Field beans, soybean, pea, lentil etc. 5.5-7.0

Groundnut 5.3-6.6

Others

Sugarcane 6.0-7.5

Cotton 5.0-6.5

Potato 5.0-5.5

Tea 4.0-6.0

2.5. Acid Sulphate soils

Acid sulphate are drained coastal wetland soils that have become acid (pH<4) due to oxidation of the pyritic

minerals in the soil. Undrained soils containing pyrites need not be acid and they are called potential acid sulphate soils.

Types of acid sulphate soils

Potential acid sulphate soils

ASS which have not been oxidised by exposure to air are known as potential acid sulfate soils (PASS). They are

neutral in pH (6.5–7.5) , contain unoxidised iron sulfides, are usually soft, sticky and saturated with water and are

usually gel-like muds but can include wet sands and gravels have the potential to produce acid if exposed to oxygen

Actual acid sulphate soils

When PASS are exposed to oxygen, the iron sulfides are oxidised to produce sulfuric acid and the soil becomes

strongly acidic (usually below pH 4). These soils are then called actual acid sulfate soils (AASS). They have a pH of less

than 4, contain oxidised iron sulfides, vary in texture and often contain jarosite (a yellow mottle produced as a by- product

of the oxidation process).Occurrence in India

Soil with sufficient sulphides (FeS2 and others) to become strongly acidic when drained are termed acid sulphate

soils or as the Dutch refer to those soils cat clays. When allowed to develop acidity, these soils are usually more acidic

than pH 4.0. Before drainage, such soils may have normal soil pH and are only potential acid sulphate soils. Generally

acid sulphate soils are found in coastal areas where the land is inundated by salt water. In India, acid sulphate soil is,

mostly found in Kerala, Orissa, Andhra Pradesh, Tamil Nadu and West Bengal.

Formation of Acid Sulphate Soils

Land inundated with waters that contain sulphates, particularly salt waters, accumulate sulphur compounds, which

in poorly aerated soils are bacterially reduced to sulphates. Such soils are not usually very acidic when first drained in

water.

When the soil is drained and then aerated, the sulphide (S2-) is oxidized to sulphate (SO2-4) by a combination of

chemical and bacterial actions, forming sulphuric acid (H2SO4). The magnitude of acid development depends on the

amount of sulphide present in the soil and the conditions and time of oxidation. If iron pyrite (FeS2) is present, the

oxidized iron accentuates the acidity but not as much as aluminium in normal acid soils because the iron oxides are less

soluble than aluminium oxides and so hydrolyze less.

Characteristics

Acid sulphate soils contain a sulphuric horizon which has a pH of the 1 : 1 soil : water ratio of less than 3.5,plus

some other evidences of sulphide content (Yellow colour). Such strong acidity in acid sulphate soils results toxicities of

aluminium and iron, soluble salts (unless leached), manganese and hydrogen sulphide (H2S) gas. Hydrogen sulphide (H2S)

often formed in lowland rice soils causing akiochi disease that prevents rice plant roots from absorbing nutrients.

Management of Acid Sulphate Soils

Management techniques are extremely variable and depend on many specific factors viz, the extent of acid formation, the

thickness of the sulphide layer, possibilities of leaching or draining the land etc. The general approaches for reclamation are

suggested bellow:

Keeping the area flooded. Maintaining the reduced (anaerobic). Soil inhibits acid development, the use of the area to rice

growing. Unfortunately, droughts occur and can in short time periods cause acidification of these soils. The water used to flood

the potential acid sulphate soils often develop acidity and injure crops. Controlling water table. If a non-acidifying layer covers

the sulphuric horizon, drainage to keep only the sulphuric layer under water (anaerobic) is possible. Liming and leaching. Liming

is the primary way to reclaim any type of acid soil. If these soils are leached during early years of acidification, lime requirements

are lowered. Leaching, however, is difficult because of the high water table commonly found in this type of soil and low

permeability of the clay. Sea water is sometimes available for preliminary leaching.

2.6. Calcareous soil

Calcareous soil that contains enough free calcium carbonate (CaCO3)and give effervescence visibly releasing

CO2 gas when treated with dilute 0.1 N hydrochloric acid. The pH of calcareous soil is > 8.5 and it is also regarded as an

alkaline (Basic) soil.

Formation

The soil are formed largely by the weathering of calcareous rocks and fossil shell beds like varieties of chalk, marl

, lime stone and frequently a large amount of phosphates. Soils are often very fertile. Soils also can become calcareous

through long term irrigation with water contains small amounts of dissolved CaCO3 that can accumulate with time.

Calcareous soils can contain from 3% to >25% CaCO3 by weight with pH values with a range of 7.6 to 8.3.

Management of Calcareous soil

Fertilizer management in calcareous soils is different from that of non calcareous soils because of the effect of soil

pH on soil nutrient availability & chemical reactions that affect the loss or fixation of some nutrients. The presence of

CaCO3 directly or indirectly affects the chemistry & availability of nitrogen (N) Phosphorus(P), Magnesium(Mg),

Potassium (K), Manganese (Mn), Zinc (Zn) and iron (Fe). The availability of copper (Cu) also is affected. Application of

acid forming fertilizers such as ammonium sulphate and urea fertilizers, sulphur compounds, organic manures and green

manures considered as effective measures to reduce the pH of soil to neutral pH value

2.7. Man made polluted soils

Soil contamination is the presence of man-made chemicals or other alteration of the natural soil environment. This

type of contamination typically arises from the rupture of underground storage tanks, application of pesticides, percolation

of contaminated surface water to subsurface strata, leaching of wastes from landfills or direct discharge of industrial

wastes to the soil. The most common chemicals involved are petroleum hydrocarbons, solvents, pesticides, lead and other

heavy metals. This occurrence of this phenomenon is correlated with the degree of industrialization and intensity of

chemical usage. The concern over soil contamination stems primarily from health risks, both of direct contact and from

secondary contamination of water supplies.

The unscientific disposal of untreated or under-treated effluents has resulted in accumulation of heavy metals in

land and water bodies. Heavy metal contamination due to the sewage and sludge application to soils imposes a major

limitation on potential land use. Cultivated areas under peri-urban agriculture are worst affected by this problem. The

heavy metals accumulating in soil may get entry into the human and animal food chain through the crops grown on it. In

Tamil Nadu State, where 55% of India’s tanning industry is located, over 35 000 ha of land have become unfit for

agriculture. Pollution from tannery effluent has rendered areas unsuitable for rice and sugar cane, declining by 40% and

80% respectively. The quality of coconuts produced on contaminated land deteriorated, making them no longer

commercially viable. Villagers also reported skin rashes from contact with well water. In many areas of Tamil Nadu

pollution to groundwater forced villagers to travel 4-5 km for water. Much of this contaminated groundwater became

unsuitable for irrigation, and estimated 600-900 wells in the region fell into disuse.

Heavy metals prevailing in soils and their regulatory limits

Elements Conc. range Regulatory limit

(mg kg-1) (mg kg-1)

Lead 1-6900 600

Cadmium 0.1-345 100

Arsenic 0.1-102 20

Chromium 0.005-3950 100

Mercury 0.01-1800 270

Copper 0.03-1550 600

Zinc 0.15-5000 1500

Management of soil pollution

Bioremediation

Bioremediation can be defined as any process that uses microorganisms, fungi, green plants or their enzymes to

return the environment altered by contaminants to its original condition. Bioremediation may be employed to attack

specific soil contaminants, such as degradation of chlorinated hydrocarbons by bacteria. An example of a more general

approach is the cleanup of oil spills by the addition of nitrate and / or sulfate fertilizers to facilitate the decomposition of

crude oil by indigenous or exogenous bacteria.

Important and widely reported hyper-accumulators used for metal

Remediation Microorganisms used for metal remediation

3.Biological problems in soils3.1.SOC and microbial population

Biological problems often results from management practices and anthropogenic influence. Soil organic carbon

(SOC) is the main source of energy for soil microorganisms and a trigger for nutrient availability through mineralization.

Humus participates in aggregate stability, and nutrient and water holding capacity. Organic acids (e.g., oxalic acid),

commonly released from decomposing organic residues and manures, prevents phosphorus fixation by clay minerals and

improve its plant availability, especially in subtropical and tropical soils. An increase in SOM, and therefore total C, leads to

greater biological diversity in the soil.

Problems

A direct effect of poor SOC is reduced microbial biomass activity, and nutrient mineralization due to a shortage of

energy sources. In non- calcareous soils, aggregate stability, infiltration, drainage, and airflow are reduced. Low SOC

results in less diversity in soil biota with a risk of the food chain equilibrium being disrupted, which can cause disturbance

in the soil environment (e.g., plant pest and disease increase, accumulation of toxic substances).

Improving Carbon Levels

No till farming, continuous application of manure and compost, and use of summer and/or winter cover crops.

Burning, harvesting, or otherwise removing residues decreases SOC.

3.2. Earthworms

Earthworms play a key role in modifying the physical structure of soils by producing new aggregates and pores,

which improves soil tilth, aeration, infiltration, and drainage. Earthworms produce binding agents responsible for the

formation of water-stable macro-aggregates. They improve soil porosity by burrowing and mixing soil. As they feed,

earthworms participate in plant residue decomposition, nutrient cycling and redistribution of nutrients in the soil profile.

Their casts, as well as dead or decaying earthworms, are a source of nutrients. Roots often follow earthworm burrows and

uptake available nutrients associated with casts.

87

Problems

Low or absent earthworm populations are an indicator of little or no organic residues in the soil and/or high soil

temperature and low soil moisture that are stressful not only to earthworms, but also for sustainable crop production.

Earthworms stimulate organic matter decomposition. Lack of earthworms may reduce nutrient cycling and availability for

plant uptake. Additionally, natural drainage and aggregate stability can be reduced.

Improving Populations

The practices that boost earthworm populations are Tillage Management (no-till, strip till, ridge till), Crop Rotation

(with legumes) and Cover Crops, Manure and Organic By-product Application , Soil Reaction (pH) Management and

proper irrigation or drainage

3.3. Soil Respiration

Carbon dioxide (CO2) release from the soil surface is referred to as soil respiration. This CO2 results from several

sources, including aerobic microbial decomposition of soil organic matter (SOM) to obtain energy for their growth and

functioning (microbial respiration), plant root and faunal respiration, and eventually from the dissolution of carbonates in

soil solution. Soil respiration is one measure of biological activity and decomposition and also known as carbon

mineralization.

Soil respiration reflects the capacity of soil to support soil life including crops, soil animals, and microorganisms.

In the laboratory, soil respiration can be used to estimate soil microbial biomass and make some inference about nutrient

cycling in the soil. Soil respiration also provides an indication of the soil's ability to sustain plant growth.88

Problems

Reduced soil respiration rates indicate that there is little or no microbial activity in the soil. It may also signify that

soil properties that contribute to soil respiration (soil temperature, moisture, aeration, available N) are limiting biological

activity and SOM decomposition. With reduced soil respiration, nutrients are not released from SOM to feed plants and

soil organisms. This affects plant root respiration, which can result in the death of the plants. Incomplete mineralization of

SOM often occurs in saturated or flooded soils, resulting in the formation of compounds that are harmful to plant

roots,(e.g. methane and alcohol). In such anaerobic environments, denitrification and sulphur volatilization usually occur,

contributing to greenhouse gas emissions and acid deposition.

Improving Soil Respiration

The rate of soil respiration under favorable temperature and moisture conditions is generally limited by the supply

of SOM. Agricultural practices that increase SOM usually enhance soil respiration.

3.4. Soil Enzymes

Soil enzymes increase the reaction rate at which plant residues decompose and release plant available nutrients.

Enzymes are specific to a substrate and have active sites that bind with the substrate to form a temporary complex. The

enzymatic reaction releases a product, which can be a nutrient contained in the substrate.

Problems

Absence or suppression of soil enzymes prevents or reduces processes that can affect plant nutrition. Poor enzyme

activity (e.g., pesticide degrading enzymes) can result in an accumulation of chemicals that are harmful to the

environment; some of these chemicals may further inhibit soil enzyme activity.

Improving Enzyme Activity

Organic amendment applications, crop rotation, and cover crops can be used to enhance enzyme activity The

positive effect of pasture is associated with the input of animal manure and less soil disturbance.

.Agricultural methods that modify soil pH (e.g., liming) can also change enzyme activity.

4. Eroded soils

Soil erosion is defined as the detachment and transportation of soil mass from one place to another through the

action of wind, water in motion or by the beating action of rain drops. Erosion extensively occurs in poorly aggregated

soils (low humus) and in a higher percentage of silt and very fine sand. Erosion increases when soil remains bare or

without vegetation. In India about 86.9% soil erosion is caused by water and 17.7% soil erosion is caused by wind. Out of

the total 173.6 Mha of total degraded land in India, soil erosion by wind and water accounts for 144.1 Mha (Govt. of India,

1990). The surface soil is taken away by the runoff causing loss of valuable topsoil along with nutrients, both native and

applied. In India about 5334 million tones (16.35 tonnes/ha/year) of soil is being eroded annually due to agriculture and

associated activities and 29% of the eroded materials are permanently lost into the sea.

Types of erosion

Natural or geologic erosion ranges from very little in undisturbed lands to extensive in steep arid lands. Geological erosion takes

place, as a result of the action of water, wind, gravity and glaciers and it takes place, at such slow rates that the loss of soil is

compensated for the formation of new soil under natural weathering processes. It is sometimes referred to as normal erosion.

Accelerated erosion caused by the disturbances of people (cutting forests, cultivating lands, constructing roads and buildings

etc.) and is increasing as the population increases. In this erosion, the removal of soil takes place at a much faster rate than that of

soil formation. It is also referred to as abnormal erosion.

4.1. Causes of Water Erosion

Water erosion is due to the dispersive action, and transporting power of water. Water erosion of soil starts when raindrops

strike bare soil peds and clods, resulting the finer particles to move with the flowing water as suspended sediments. The soil

along with water moves downhill, scouring channels along the way. Each subsequent rain erodes further amounts of soil until

erosion has transformed the area into barren soil. Water erosion may occur due to the removal of protective plant covers by

tillage operation, burning crop residues, overgrazing, overcutting forests etc. inducing loss of soil.

Raindrop / Splash Erosion.

Rain drop splash erosion results from soil splash caused by the impact of falling rain drops. The continued impact of

raindrops compacts the soil and further seals the surface-so that water cannot penetrate into the soil and as a result causing more

surface run off.

Sheet Erosion

Sheet erosion is the removal of a fairly uniform layer of surface soil by the action of rainfall and runoff water on

lands having a gentle or mild slope, and results in the uniform "skimming off of the cream" of the top soil with every hard

rain, In this erosion, shallow soils suffer greater reduction in productivity than deep soils. It is slow process but dangerous.

Movement of soil by rain drop splash is the primary cause of sheet erosion.

Rill Erosion

Rill erosion is the removal of surface soil by running water, with the formation of narrow shallow channels that can

be levelled or smoothed out completely by normal cultivation. Rill erosion is more apparent than sheet erosion. Rill

erosion is more serious in soils having a loose shallow top soil. This type of soil erosion may he regarded as a transition

stage between sheet and gully erosion.

Gully Erosion

Gully erosion is the removal of soil by running water, with the formation of channels that cannot be smoothed out

completely by normal agricultural operation or cultivation. Gully erosion is an advanced stage of rill erosion. Unattended

rills get" deepened "and widened every year and begin to attain the form 'of "gullies. During every rain, the rain water

rushes down these gullies, increasing their width, depth and length.(Fig :8)

Stream Channel Erosion

eam channel erosion is the scouring of material from the water channel and the cutting of banks by flowing or

running water. This erosion occurs at the lower end of stream tributaries. Stream bank erodes either by runoff flowing over

the side of the stream bank, or by scouring or undercutting. Scouring is influenced by the velocity and direction of flow,

depth and width of the channel and soil texture.

Harmful Effects of Water Erosion/Constraints

Water erosion causes various damages to the lands as follows:

(i)Loss of top fertile soil: The surface soil lost as runoff consists of fertile soils and fresh or active organic matter.

(ii)Accumulation of sand or other unproductive coarse soil materials on other productive lands. In the plains, fertile lands

have been made unproductive by the deposition or accumulation of soil material brought down from the hills by streams

and rivers.

(iii)Silting of lakes and reservoirs. Soil erosion from the catchment areas of reservoirs results in the deposition of soil, thus

reducing their storage capacity

(iv)Silting of drainage and water channels. Deposition of silt in drainage ditches in natural streams and rivers reduces their

depth and capacity and overflows and flooding of downstream areas increase with damage to agricultural crops and

also man-made structures.

(v)Decreases water table: With the increase in runoff, the amount of water available for entering the soil is decreased. This

reduces the supply of water to replenish the ground water in wells, the yield of well is reduced.

(vi)Fragmentation of land. Water erosion especially gully erosion may divide the land into several valleys and ridges and

thus fields become smaller and more numerous. Crop rows are shortened, movement from field to field is obstructed and a

result the value of land is decreased.

4.2. Wind erosion

Soil erosion by wind has caused an accumulation of eroded particles in loess, a type of soil which makes up some

of the world's most fertile and productive regions. Soil conditions conducive to wind erosion are most commonly found in

arid and semi-arid areas where rainfall is insufficient and no vegetative cover on the land. The most serious damage caused

by wind erosion is the change in soil texture. Since the finer soil particles are subject to movement by wind, wind erosion

gradually removes silt, clay and organic matter from the top soil, leaving the coarser soil material.

Wind erodes the soil in three steps

The soil particles are carried by the wind in three ways namely saltation, suspension and surface creep.

Saltation: It is a process of soil movement in a series of bounces or jumps. Soil particles having sizes ranging from 0.05 to

0.5 mm generally move in this process. Saltation movement is caused by the pressure of the wind on the soil particle, and

collision of a particle with other particles. The height of the jumps varies with the size and density of the soil particles, the

roughness of the soil surface, and the velocity of the wind.

Suspensio:. Suspension represents the floating of small sized particles in the air stream. Movement of such fine particles

in suspension is usually started by the impact of particles in saltation. Once these fine particles are picked up by the

particles in saltation and enter the turbulent air layers, they can be lifted upward in the air and .they are often carried for

several miles before being redeposit elsewhere. Dust particles will fall on the surface only when the wind subsides or the

rain washes them down.

Surface Creep: Surface creep is the rolling or sliding of large soil particles along the ground surface. They are too heavy

to be lifted by the wind and are moved primarily by the impact of the particles in saltation rather than by direct force of the

wind. The coarse particles tend to move closer to the ground than the fine ones.

Threshold Velocity: Threshold velocity is the minimum wind velocity required to initiate the movement of soil particles.

Threshold velocity varies with the soil conditions and nature of ground surface.

Impact of erosion on crop yield

∙Erosion reduces the capacity of the soil to hold water leading to severe water stress.

∙Erosion contributes to losses of plant nutrients, which wash away with the soil particles. Because sub-

soils generally contain fewer nutrients than top-soils, more fertilizer is needed to maintain crop yields. This, in

turn, increases production costs. Moreover, the addition of fertilizer alone cannot compensate for all the nutrients

lost when topsoil erodes.

∙Erosion reduces yields by degrading soil structure, increasing soil erodibility, surface sealing

∙and crusting. Water infiltration is reduced, and seedlings have a harder time breaking through the soil crust.

Erosion reduces productivity because it does not remove topsoil uniformly over the surface of a field. Typically,

parts of an eroded field still have several inches of topsoil left; other parts may be eroded down to the subsoil.

This makes it practically impossible for a farmer to manage the field properly, to apply fertilizers and chemicals uniformly and obtain uniform results. He is also unable to time his planting, since an eroded part of the field may

be too wet when the rest of the field is dry and ready.

Best Management Practices: that are used to control erosion factors of both wind and water are

∙Crop rotation- improves the overall efficiency of nitrogen uptake and utilization in the soil. If certain cover

crops are planted in the winter, erosion and runoff is prevented when the ground thaws, and nutrients are trapped

in the soil and released to the spring crops.

∙Contour cultivation- On gently sloping land, a special tillage practice carried out on the contour of the field can

reduce the velocity of overland flow. Contour cultivation should not be carried out on steep slopes because it will

merely make the erosion situation worse.

∙Strip cropping- It is a technique in which alternate strips of different crops are planted in the same field. There

are three main types: contour strip cropping, field strip cropping, and buffer strip cropping. If the strips are

planted along the contour, water damage can be minimized; in dry regions, if the strips are planted crosswise to

the contour, wind damage is also minimized.

∙Terraces- Constructing bench-like channels is otherwise known as terraces, enables water to be stored

temporarily on slopes to allow sediment deposition and water infiltration. There are three types of terraces: bench

terraces

∙contour terraces, and parallel terraces. It will control erosion in wetter areas by reducing the length of the slope. ∙Grassed Waterways - They force storm runoff water to flow down the center of an established grass strip and

can carry very large quantities of storm water across a field without erosion. Grass waterways are also used asfilters to remove sediment, but may sometimes lose their effectiveness when too much sediment builds up in thewaterways. To prevent this, it is important that crop residues, buffer strips, and other erosion control practicesand structures be used along with grass waterways for maximum effectiveness.

Diversion structures- These are channels that are constructed across slopes that cause water to flow to a desiredoutlet. They are similar to grass waterways and are used most often for gully control.

Drop structures - Are small dams used to stabilize steep waterways and other channels. They can handle largeamounts of runoff water and are effective where falls are less than 2.5 meters

Riparian strips - These are merely buffer strips of grass, shrubbery, plants, and other vegetation that grow on thebanks of rivers and streams and areas with water conservation problems. The strips slow runoff and catchsediment. In shallow water flow, they can reduce sediment and the nutrients and herbicides attached to it by 30%to 50%.

No-till planting- This planting system prepares a seedbed 2 inches wide or less, leaving most of the surfaceundisturbed and still covered with crop residues. The result is a wetter, colder environment that protects the seedand soil with its insulating effect of the surface residue.

∙Strip Rotary- Tillage A strip four to eight inches wide and two to four inches deep is prepared by a rotary tiller,

while the rest of the soil is left undisturbed. The soil is conserved because of the crop residues between the tillage

strips

∙Till Planting -This plowing technique sweeps the crop residues into the area between the rows of crops. Soil

density between these rows remains relatively high because of the absence of tillage. This soil is difficult for

raindrops to detach and runoff to move.

∙Annual Ridges - Also known as permanent ridges or ridge tillage, the annual ridges are formed by using a

rolling disk bedder, and planting is done after only minor spring seedbed preparation. The extent of soil

conservation depends on the amount of residue left and the row direction. Planting on the contour plus increased

surface residues greatly reduce soil loss.

∙Chiseling- This system does not turn the soil over, but rather leaves it rough and cloddy with plenty of crop

residue remaining. The soil density and amount of covering depends on the depth, size, shape, spacing, and so on

of the chisel blades. The residue and rough, cloddy surface of the soil reduces raindrops impact and reduces

runoff velocities thus reducing erosion.

∙Disking- This system pulverizes the soil and gives great soil density The effect is similar to that of chiseling

with results also depending on the depth, size, spacing, and so on of the disk blades. The deeper the disking, the

fewer the residues that remain on the surface.Sustaining soil health is the imminent need of the hour

Soil health is defined as the continued capacity of soil to function as a vital living system, which include sustaining

biological productivity of soil, maintain the quality of surrounding air and water environments, as well as promote plant,

animal, and human health. Soil function include sustaining biological diversity, activity and productivity, regulating water

and solute flow, filtering, buffering, degrading organic and inorganic materials, storing and cycling nutrients and carbon,

providing physical stability and support.

Soil health deals with both the inherent and dynamic soil quality. The former relates to the natural (genetic)

characteristics of the soil (e.g., texture), which are the result of soil-forming factors. They are generally cannot easily be

amended. On the other hand, the dynamic soil quality component is readily affected by management practices and relates

to the levels of compaction, biological functioning, root proliferation, etc which is of most interest to growers because

good management allows the soil to come to its full potential.

Soil quality or health cannot be determined by measuring only crop yield, water quality, or any other single

outcome but with indicators which are measurable properties of soil or plants that provide clues about how well the soil

can function.

Indicator Relationship to Soil Health

Soil fertility, structure, stability, nutrientSoil organic matter (SOM)retention; soil erosion

Physical: soil structure, depth of soil, infiltration and bulk density; water holding capacity

Retention and transport of water and nutrients; habitat for microbes; estimate of crop productivity potential; compaction,

plow pan, water movement; porosity; workability

Chemical: pH; electrical conductivity; extractable N- P-K

Biological and chemical activity thresholds; plant and microbial activity thresholds; plant available nutrients and potential

for N and P lossBiological: microbial biomass C and N; potentially mineralizable N; soil respiration. Microbial catalytic potential andrepository for C and N; soil productivity and N supplying potential; microbial activity measure

In the International Year of soils, policy makers, scientists and all stake holders should pledge to really protect the

soil through multifaceted approach including input management like water, manures, fertilizers and revamp soil health

management programmes and evolving more soil health indicators specific to a region and resort to more of physical and

biological fertility management and precise agriculture which naturally will take care of all other functions. Many

interactions hitherto neglected involving soil, plant, microbe, water and atmosphere should be focussed. Sustainable soil

management is essential for getting food, feed, fibre, fuel, medicines and ecosystem services. It is a non renewable

resource and managing sustainably needs increasing soil organic matter content, using nutrients wisely, keeping soil

surface vegetated, promoting crop rotations and diversification and reducing erosion. It is imperative to solve the soil

constraints and make the lands highly productive on a sustainable basis, we need to develop technologies suitable to

specific locations which will be economically feasible and workable at farmer’s field. Though emphasis is on increasing

the current yield level, attention should also be given to prevent soil degradation and also develop suitable technologies to

reclaim the problem soils.

The nation that destroys soil destroys itself – Franklin Roosevelt, 1937

THE QUALITY OF IRRIGATION WATER

3.1 The suitability of irrigation water depends upon several factors, such as, water quality,soil type, plant characteristics, irrigation method, drainage, climate and the local conditions. Theintegrated effect of these factors on the suitability of irrigation water (SI) can be qualitativelyexpressed by the relationship:

SI = QSPCDwhereQ = quality of irrigation water, that is, total salt concentration, relative proportion of cations, etc;S = soil type, texture, structure, permeability, fertility, calcium carbonate content, type of clay

minerals and initial level of salinity and alkalinity before irrigation;P = salt tolerance characteristics of the crop and its varieties to be grown, and growth stage;C = climate, that is, total rainfall, its distribution and evaporation characteristics; andD = drainage conditions, depth of water table, nature of soil profile, presence of hard pan or lime

concentration and management practices.

3.1.1 These factors act interactively. For example; in a particular climate, all the factorsenumerated in 3.1, are likely to vary and interact either positively or negatively in relationto salt accumulation and degree of harmful effect on soil properties and crop growth. Assuch, a single suitable criterion is hard to be adopted for widely varying conditions.However, a general broad guideline has been developed for use by the field practitioners.

3.2 Besides these factors, presence of some ions in water such as calcium, sulphate,potassium and nitrate is favourable for crop growth, as water of more salinity can be used inpresence of these ions.

4. WATER QUALITY CRITERIA FOR IRRIGATION

4.1 The following chemical properties shall be considered for developing water qualitycriteria for irrigation:

a) Total salt concentration,b) Sodium adsorption ratio,c) Residual sodium carbonate or bicarbonate ion concentration,

andd) Toxic elements such as sodium, boron, fluoride, heavy metals etc.

5. WATER QUALITY RATING IN RELATION TO SOIL TYPE, RAINFALL ANDCROP TOLERANCE TO SALTS

5.1 Upper permissible limit of electrical conductivity (EC) are given in Table 3 keepingin view the soil types, rainfall and three types of crops i.e. Sensitive (S), Semi-tolerant (ST)and Tolerant (T).

TABLE 3. Suitability of poor quality saline ground waters (RSC < 2.5 me/l, SAR <10(mmol/l)1/2) for irrigation in India

Soil texture group Crop toleranceECiw (dS/m) limit for rainfall (mm) region

< 350 350-550 > 550Fine(>30 % clay)Sandy clay, clay loam,silty clay loam, silty clay,clay

S 1.0 1.0 1.5ST 1.5 2.0 3.0T 2.0 3.0 4.5

Moderately fine(20 to 30 % clay )Sandy clay loam, loam,silty loam

S 1.5 2.0 2.5ST 2.0 3.0 4.5T 4.0 6.0 8.0

Moderately coarse(10 to 20 % clay)Sandy loam, loam, siltyloam

S 2.0 2.5 3.0ST 4.0 6.0 8.0T 6.0 8.0 10.0

Coarse(<10% clay)Sand, loamy sand, sandyloam, silty loam, silt

S -- 3.0 3.0ST 6.0 7.5 9.0T 8.0 10.0 12.5

NOTE – i)The use of waters of 4.0 dS/m EC and above be confined to winter season crops only. They shouldnot be used during the summer season. During emergencies not more than one or two protective irrigationsshould be given to the Kharif season crops. ii) For soils having (i) shallow water table (within 1.5 m in kharif)and (ii) presence of hard subsoil layers, the next lower ECiw is applicable.

5.2 Upper permissible limits of sodium adsorption ratio (SAR) and residual sodiumcarbonate (RSC) for semi-tolerant (ST) and tolerant (T) crops is given in Table 4.

TABLE 4. Suitability of poor quality high SAR saline and alkali ground waters (RSC> 2.5 me/l, ECiw < 4.0 dS/m) for irrigation in India

Soil texture group SAR(mmol/l)½

Upper limit ofRSC (me/l)

Remarks

ST T ST TFine(>30 % clay)Sandy clay, clayloam, silty clayloam, silty clay,clay

10 15 2.5 3.5 Limits pertain to khariffallow/Rabi crop rotation whenannual rainfall is 350-550 mm.

When the waters have Na <75%, (Ca+Mg>25%) orrainfall is >550 mm, even theRSC values for tolerant cropsbecomes safe for ST crops.Grow low water requiring

Moderately fine(20 to 30 % clay )Sandy clay loam,loam, silty loam

10 20 3.5 5.0

Moderately coarse(10 to 20 % clay)Sandy loam, loam,silty loam

15 25 5.0 7.5 crops during Kharif. Avoidrice/sugarcane. Presence ofgypsum in soil is favourable.

Coarse (> 10)Sand, loamy sand,sandy loam, siltyloam, silt

20 30 7.5 10

5.3 The upper permissible limits of boron for ST and T crops are given in Table 5.

TABLE 5. Suitability of irrigation water for semi-tolerant and tolerant crops indifferent soil types

Sl. No. Soil Textural Group Upper permissible limit ofboron (mg/l)

ST T1 Fine (Above 30 percent clay)

Sandy clay, clay loam, silty clay loam, silty clay,clay

2 3

2 Medium (20-30 percent clay)Sandy clay loam, loam, silty loam

2 3

3 Moderately coarse (10-20 Percent clay) Sandyloam, loam, silty loam

2 3

4 Coarse (< 10 percent clay)Sand, loamy sand, sandy loam, silty loam, silt

1 2

5.4 Upper permissible limits of various toxic ions and elements are reported in Table 6.

TABLE 6. Upper permissible concentrations of trace elements in irrigation water1

Element

RecommendedMaximum

Concentration2

(mg/l)

Remarks

Al (aluminium) 5.0 Can cause non-productivity in acid soils (pH < 5.5), butmore alkaline soils at pH > 7.0 will precipitate the ionand eliminate any toxicity.

As (arsenic) 0.10 Toxicity to plants varies widely, ranging from 12 mg/l forSudan grass to less than 0.05 mg/l for rice.

Be (beryllium) 0.10 Toxicity to plants varies widely, ranging from 5 mg/l forkale to 0.5 mg/l for bush beans.

Cd (cadmium) 0.01 Toxic to beans, beets and turnips at concentrations as lowas 0.1 mg/l in nutrient solutions. Conservative limitsrecommended due to its potential for accumulation inplants and soils to concentrations that may be harmful to

humans.

Co (cobalt) 0.05 Toxic to tomato plants at 0.1 mg/l in nutrient solution.Tends to be inactivated by neutral and alkaline soils.

Cr (chromium) 0.10 Not generally recognized as an essential growth element.Conservative limits recommended due to lack ofknowledge on its toxicity to plants.

Cu (copper) 0.20 Toxic to a number of plants at 0.1 to 1.0 mg/l in nutrientsolutions.

F (fluoride) 1.03 Inactivated by neutral and alkaline soils.

Fe (iron) 5.0 Not toxic to plants in aerated soils, but can contribute tosoil acidification and loss of availability of essentialphosphorus and molybdenum. Overhead sprinkling mayresult in unsightly deposits on plants, equipment andbuildings.

Li (lithium) 2.5 Tolerated by most crops up to 5 mg/l; mobile in soil.Toxic to citrus at low concentrations (<0.075 mg/l). Actssimilarly to boron.

Mn (manganese) 0.20 Toxic to a number of crops at a few-tenths to a few mg/l,but usually only in acid soils.

Mo (molybdenum) 0.01 Not toxic to plants at normal concentrations in soil andwater. Can be toxic to livestock if forage is grown in soilswith high concentrations of available molybdenum.

Ni (nickel) 0.20 Toxic to a number of plants at 0.5 mg/l to 1.0 mg/l;reduced toxicity at neutral or alkaline pH.

Pd (lead) 5.0 Can inhibit plant cell growth at very high concentrations.

Se (selenium) 0.02 Toxic to plants at concentrations as low as 0.025 mg/land toxic to livestock if forage is grown in soils withrelatively high levels of added selenium. An essentialelement to animals but in very low concentrations.

Sn (tin)

Ti (titanium) ---- Effectively excluded by plants; specific toleranceunknown.

W (tungsten)

V (vanadium) 0.10 Toxic to many plants at relatively low concentrations.

Zn (zinc) 2.0 Toxic to many plants at widely varying concentrations;reduced toxicity at pH > 6.0 and in fine textured ororganic soils.

1 Adapted from National Academy of Sciences (1972) and Pratt (1972).

2 The maximum concentration is based on a water application rate which is consistent with good irrigation practices (10 000m3 per hectare per year). If the water application rate greatly exceeds this, the maximum concentrations should be adjusteddownward accordingly. No adjustment should be made for application rates less than 10 000 m3 per hectare per year. Thevalues given are for water used on a continuous basis at one site.

3 Under the tropical climatic condition this limit seems to be to conservative foe irrigation water and need to be revised

6. SALT TOLERANCE OF CROPS

6.1 There are intra-generic and inter-generic differences in salt tolerance of crops andthis character of crops and crop varieties could be exploited to use saline/alkali water. Thedata presented in Tables 7, Table 8 and Table 9 presents the relative tolerance of salts to soilsalinity, soil alkali and boron. These tables could be used to select crops depending upon thekind and degree of the problem with water.

TABLE 7. Crop groups based on response to soil salinitySensitive Group

----------------------------------------Highly sensitive Medium sensitive

Resistant Group----------------------------------------

Medium tolerant Highly tolerantLentil Radish Spinach BarleyMash Cow pea Sugarcane CottonChickpea Broad bean Indian mustard Sugar beetBeans Vetch Rice (transplanted) TurnipPeas Cabbage Wheat TobaccoCarrot Cauliflower Pearl millet SafflowerOnion Cucumber Oats RapeseedLemon Gourds Alfalfa Karnal grassOrange Tomato Blue panic grass Date palmGrape Sweet potato Para grass BerPeach Sorghum Rhodes grass MesquitePlum Minor millets Sudan grass CasuarinaPear Maize Guava TamarixApple Clover, berseem Pomegranate Salvadora

Acacia

TABLE 8. Relative tolerance of crops to alkali stress

Characteristics ESP range* Crops

Sensitive 10-15 Safflower, mash, peas, lentil, pigeon pea, urdbean

16-20 Chickpea, soybean

20-25 Groundnut, cowpea, onion, pearl millet

Semi-tolerant 25-30 Linseed, garlic, guar

30-50 Indian mustard, wheat, sunflower

Tolerant 50-60 Barley, Sesbania

60-70 Rice (Transplanted)

*Relative yields are only 50% of the potential in respective alkali range

TABLE 9. Relative tolerance of crops to boron

Sensitive (<1 mg/l) Semi tolerant (1.0-2.0 mg/l) Tolerant (2.0-4.0 mg/l)Apple Sunflower Date palmGrape Potato Sugar beetCherry Cotton Garden beetPeach Tomato AlfalfaOrange Radish GladiolusGrapefruit Field pea Broad beanLemon Barley Onion

Wheat TurnipCorn CabbageRice LettuceOat CarrotBell pepper CauliflowerSweet potato

6.2 Tolerance to Chloride

The relative tolerance of crop to chloride in order of sensitive to tolerant are: dry bean,onion, carrot, lettuce, pepper, corn, potato, alfalfa, Sudan grass, wheat, sorghum, sugar beet,barley.

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