Transcript Environmental conditions that affect plant growth

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 to
what happens on NZ West Coasts.
Warm wet air comes in and hits the hills on the seaward west coast, the moist air rises
producing rain. The air then descends and warms before rising up over the alps. As it
cools it turns into snow (alps). The air is now dry as it comes over the Alps with no
moisture left, as it travels across the plains it turns into the warmer winds on the
Canterbury 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 wind
For 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:
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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:
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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
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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:
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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
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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