PHYSICAL FACTORS OF THE ENVIRONMENT

AND TECHNIQUES USED TO

MODIFY THEM FOR

PLANT PRODUCTION

The average weather conditions over a long period of time in an area are known as its climate.

• The climate stays fairly constant as it is measured over a period of many days and then recorded over many years.

• The average climate is seen more easily in the months. The average temperatures and rainfall for various months have been recorded for several years.

The changing day to day conditions are known as an areas weather.

• The weather has an immediate influence on the level of output from a farm and on the efficiency of any particular farming activity.

• The weather often has out of the ordinary results e.g. highest temperature recorded in 50 years.

• The main aspects of weather studied by scientists are:

• Solar radiation

• Temperature

• Rainfall

• Evaporation rates

• Humidity

• Wind effects.

• With an increase in altitude, comes a decrease in average temperatures. There is also more unsettled weather in these higher altitudes.

• The climate within the first kilometre of the ground has the biggest effect on plant and animal production

• Changing temperature patterns of the soil and air affect the germination, growth and development rates of plants.

• Climate changes also affect animal production levels as they affect the availability of feed and water, they also have effects on body metabolism and behaviour.

WEATHER

• Weather has a major effect on agricultural and horticultural production in NZ.

• The weather is one of the things that farmers have little control over.

• We can attempt to minimise the effects of the weather, but in the end we can only do so little.

The main factors that contribute to NZ’s weather are:

• The movement of air from areas of high pressure to areas of low pressure (wind)

• The small land mass and the long narrow shape of the islands of NZ with a central ridge of mountains

• The vast areas of water surrounding the country• Its location in the path of a massive westerly air stream.

Land and sea absorb different amounts of heat from the sun and this factor also contributes to NZ’s coastal weather patterns. As the land heats up, the air above it rises and is replaced by cooler air from over the sea. This air movement creates wind.

Diagram Above: Annual precipitation profile in the Sierra Nevada Mountain: similar towhat happens on NZ West Coasts.Warm wet air comes in and hits the hills on the seaward west coast, the moist air risesproducing rain. The air then descends and warms before rising up over the alps. As itcools it turns into snow (alps). The air is now dry as it comes over the Alps with nomoisture left, as it travels across the plains it turns into the warmer winds on theCanterbury plains. It also produces similar effects in the North Island.

Air Pressure:

• Air pressure is the weight of all the air directly above an area.

• Air pressure decreases with increasing height above sea level.

• Air pressure is measured using a barometer.

Weather Maps:

• Weather maps are drawn to show what is happening with weather systems at a particular time.

• High pressure also known as an anticyclone. It is marked with an “H” on weather maps.

• In the southern hemisphere wind circulates in an anticlockwise direction.

• Low pressure also known as a depression.• It is marked with an “L” on weather maps.• In the southern hemisphere wind circulates

in a clockwise direction.• Isobars are the lines on the weather map.• They connect places of similar atmospheric

pressure.• The lines also show the direction of the

wind and indicate its strength by how close together they are. The closer the lines, the more windy it is.

WIND

Wind has a major effect on agricultural and horticultural production in NZ.

• The prevailing winds are the most common winds in an area.

• NZ has a westerly wind pattern due to the earth’s spin.• This is changed in some areas by local features and

topography.• Strong moist northerly winds are common in Wellington

in spring, these damage blossom and new plant growth.• Nor’westers in Canterbury are important during grain

drying.

•Wind can be measured using the Beaufort scale.

Effects of windFor each of the following problems, make notes on why it is

not good.Wind can cause many problems including:

1. Increased erosion and removal of topsoil as dust.

2. Increased evaporation rates from plants and soil.

3. Increased transpiration rates of plants.

4. Spreading of air-borne diseases e.g. rust

5. Lodging of plants (when leaves become entangled), making them difficult to harvest

6. Reduced heat accumulation due to the wind chill factor

7. Spreading weed seeds, meaning more costs of removal, or lower income due to contamination of seed crops.

8. Uneven plant growth. Trees lean away from the prevailing wind.

9. Reduced or damaged plant growth. Damaged leaves do not carry out as much photosynthesis. Flowers can be damaged or blown off the plant. Wind-damaged fruit does not store as well and is less marketable. Cuticle damage to leaves causes an increase in water loss.

10. Upsetting insect movement.

11. Crops are flattened, trees are knocked down.

12. Cold chilling by dropping the air temperature, this slows plant growth because the rate of photosynthesis drops.

13. Lower air temperature can also delay flowering.

14. Plants on sheltered blocks flower before those that are unprotected.

15. Removal of the layer of humid air around the leaves which forms a protective environment. This causes:

16. May bring salt spray or cause spray drift

Positive effects of the wind:

• Reduced likelihood of frost, reduces __________

• Providing air movement that will dry the outer leaves of a plant and therefore prevent the growth of fungal diseases because __________________________________

• Assisting with the pollination of wind pollinated plants

• Aid the drying of hay or grains before harvest.

Techniques used to modify wind

• Wind speeds of 17 knots (31km/hr) will effect horticultural and agricultural production.

• Shelter is required especially in horticultural areas when wind speed is too high.

How can we modify the effects of wind?

• The use of permeable shelter is one of the most commonly used methods.

• Permeable shelter can be made of artificial materials (Shade cloth, Wooden slats(fence), Shade/glass/plastic house) or from natural (trees) material.

Advantages:

• Reduce wind speed and moisture loss• Increase soil and air temperature• Reduce wind damage to soil and plants• Can provide shading• Can provide a habitat for beneficial insects and

animals

Disadvantages:

• Can cause frosts to be more severe• Gives pests and diseases a place to survive over winter• Takes up space that could be used for other plants• Living windbreaks can compete for light, space, nutrients

and water• Cost money to set up and maintain• Can cause shading.

Natural Shelter

Advantages• cheap to set up• lasts for many years• attractive to wild life• can be multipurpose• provides shade for open drains reducing weed growth• can smother weeds• costs can be shared with the boundary neighbours• aesthetic (beautifying)

Disadvantages• continued weed control especially during establishment• possible need for irrigation especially during establishment• root systems may block tile drains• trees may blow over if planted too close to open drains• hazard to traffic visibility and leaf litter making roads greasy in

winter.• May damage transmission, power or phone lines.• may need pruning• pests and diseases may be a problem• gaps from death of some plants will need to be replaced• may need to be fenced from stock• subsoiling next to the shelterbelt every few years may be required to

prevent the roots competing with crops.

Live shelter can have functions other than wind protection if suitable species are chosen:

• Shade • erosion control• stock fodder • timber• bee fodder • stock over-wintering area• Mixed species shelterbelts live longer because they have

less disease problems. Also if one species dies out due to drought, disease, or stock damage the grower still has remaining species left for shelter. Soils tend to be improved with mixed shelter whereas stands of poplar or pines can deplete the soil of nutrients.

Artificial Shelter

Artificial windbreaks are expensive to set up and are often used for high value or short term crops. The strongest likely wind has to be considered along with the soil type to prevent the support posts blowing over.

Advantages

• a crop has instant shelter

• usually low maintenance

• takes up little space

• does not use up soil water and nutrients

• Does not have many of the disadvantages of live shelter

Disadvantages

• require replacing after several years due to damage from light and wind

• not biodegradable creating disposal problems

• expensive

• Does not have many of the advantages of live shelter