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CHAPTER 3: AGRICULTURE AND THE ENVIRONMENT

1. Soil: Formation, composition and uses
 Soil is the loose material on the earth’s surface above the solid rock.
 Soil is the topmost layer of the Earth’s crust.
 Plants need soil for growth.
 Plants in turn are the basis of the chain which supports humans and all the
land animals upon which humans feed.
 The thickness of the soil layer varies greatly from place to place.
 Most soils have three layers called horizons.
 Soil consists of organic matter (dead remains and wastes of plants and
animals), mineral matter (sand, silt and clay), water and air
 Half of the soil by volume is not solid (made up of air and water) varies because
of Weather
 Texture is the balance of mineral particles in a soil. Soil texture is important as
it affects many of factors which influence plant growth and farming like Pore
space, aeration drainage nutrients and ease of use
 Plants need minerals like nitrogen, phosphorous and potassium for healthy
growth.
 Mineral particles are formed by weathering of the rock that lies below the soil.
 In areas of natural vegetation, dead leaves and other waste matter in the soil.
This is the nutrient cycle.
 Soil acidity is measured by the pH Scale. (5.5 to 8 ideal for farming) Above 8
saline soil, below 5.5 acid soil (restrict root access to water and nutrients)
 Sandy soils are describe as hungry soils
 Best soil for farming is loamy soil.

Types of Farming

 Arable farming is growing crops only

 pastoral farming is keeping and grazing animals
 Mixed farming when farmers grow crops and keep livestock as well.
 Commercial farming is growing crops and keeping animals for sale

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i) Commercial Arable Farming (either one crop or limited, ex: Banana plantation in Central
America, operated by big companies)
ii) Commercial Pastoral Farming (one type of animal is kept for sale)
 Subsistence farming is growing crops and keeping animals mainly to feed the family. One
of the most traditional forms of Subsistence farming is shifting cultivation, widely practiced
in the tropical forests of South America and South East Asia.
Advantage: no population pressure & no serious forest destruction
Disadvantage: output is very low per hectare and less population is supported
 Extensive farming is producing a low output per hectare from large areas of land
 Intensive farming is producing high output per hectare
 Commercial arable farmers often concentrate on growing just one crop, or at best a limited
number of crops. Tropical plantation agriculture is a good example.
 In Tropical plantation agriculture one crop is widely grown on plantation in central and
South America for export worldwide.
 These plantations are owned by and operated by big companies.

Shifting cultivation in tropical rainforest

 A small plot of forest is cleared by slash and then burn
 Crops such as maize, rice and bananas are planted
 Nothing special for their growth is added to the soil. They are just harvested when ready.
 After 2/3 years, soil loses its fertility and the plot is abandoned.
 So another plot needs to be cleared to carry out to this produce again.
 Plants and small trees grow rapidly and takes over the abandoned plot

Wet rice (padi) cultivation in Asia

 Monsoon brigs heavy rains between June and September.
 Flat flood plains and deltas make flooding the fields easier
 Silt soils are fertile ,deep and easy to work

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 Large number of people living in rural areas work in the fields

 Hand labour is needed for planting seeds in nurseries, transplanting rice into the fields
harvesting and threshing rice cultivation also requires a lot of labor

 Agricultural techniques to increase to yields

1. Irrigation
 Supply of water from lakes, rivers, reservoirs etc.
 Water transferred from areas of storage used by canals
 Water sprayed by sprinklers to provide equal amount over wide area
 Ex: Hot Deserts (Egypt, Middle East etc.), Savanna and Monsoon (a dry season during
which temp is high)

2. Chemicals (fertilizers and pesticides)

 Natural shortage of mineral nutrients in a soil
 Nitrogen fertilizers, Ammonium nitrate and ammonium sulphate provide soluble
nitrogen to plants
 Insecticides to destroy crop eating insects
 Herbicide sprays can kill weeds (compete with crop for light and nutrients)
 Fungicides
 Possible to grow the same crop on the same piece of land year after year.
3. Mechanization
4. Selective breeding of plants
5. Genetically modified organisms
6. controlled environments

Genetically modified organisms

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i. Genetic engineering: It is the process of altering the genetic composition of an organism by

modifying its own genes or introducing genes from a different species. It involves the
transfer of genes from one organism to an unrelated species.
ii. Biotechnology: It is the use of living organisms or biological process for industrial,
agricultural, or medical purposes.

The different types of GM crops

i. Pest resistant Bt crops :Plants are protecting against insect damage by producing a toxin,
found in the common soil, bacterium
ii. Herbicide tolerant: that are not affected by the adverse effects of HERBICIDES.
iii. Disease resistant: that are not effected by viral plan diseases
iv. Modifying plant products: food could be produced that offered higher level of nutrients
and vitamins

Controlled environments

 Controlled environments such as greenhouses are used mainly in countries with cool
climates as in Northern America
 Hydroponics is an extreme form of glasshouse production.
Soil is replaced by mineral solution pumped around the plant root.
 In Crop rotation, with rotation crops grown on any plot of land change from one growing
season to the next.
 When one crop is replaced by another minerals taken out by one crop can be replaced by
another. Therefore a good rotation system maintains soil fertility and structure, increases
crop yield and reduces the risk of soil erosion

The adverse effects of modern agricultural practices

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(a)Overuse of chemical pesticides and inorganic fertilizers

 The water is starved of oxygen by decomposing of dead algae that process is known as
eutrophication.
 Eutrophication is due to surplus use of fertilizers, drain into water ,water plants such as
algae grow ,blocks sunlight, decomposition of dead algae, less oxygen for marine
organisms.
 Pesticides kill other organisms in the soil too, such as bacteria.
 Salinization due to the input of large quantity of water on soil surface.
(b) Overuse and mismanagement of irrigation water
 Concentration areas of irrigation water on the surface
 Salts are drawn up to the top of the soil as moisture is evaporated
 Further evaporation leaves the salts behind in the topsoil
 A hard crust salt is deposited on the surface
 Salt concentration around plant roots
 As most plants and crops cannot tolerate high salt levels, they wither and die.

(c) Over cultivation and overgrazing of farm land

 Exhaustion of mineral ion content
 Soil erosion
 desertification

Human impacts
 The worst human impact of modern agricultural practices is that the rich get richer, the poor get
poorer.
 In developing countries, modern agricultural practices favour large scale operators over small scale
farmers.
 Big farmers benefit from “Economics of scale”, this means the larger the farm, the less it costs to
cultivate on hectare of land.
 Big landowners can often make more money by specializing in growing one crop (monoculture)
instead of many crops (polyculture).
 Monoculture is less good for the soil than polyculture.

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Soil erosion: causes and impacts

(a)Causes of soil erosion
 Soil erosion is the loss of top soil by wind and water.
 Deforestation
 Overgrazing
 Overcultivation
 wrongs farming practices
 Clearance of natural vegetation.

(b) Impacts of soil erosion

 Reduction of crop yields
 Land become less productive
 Farmers spend more on fertilizers to improve yields, so their income goes
down and expenditure rises.
 Sediments of soil after being washed away settle on seabed.
 Siltation will occur with accumulation of the soil in Dams.
 They are costly to remove and increased amount of sediments in dams can
cause flooding.
 Famine
 Desertification

Causes and consequences of desertification

It is the process whereby land is turned into a desert.

(a) Causes
 Decline in rainfall

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 Overgrazing
 Over cultivation
 Irrigation and salinization
 Increased demand for food and fuel
 All these factors lead to decline in vegetation cover and so increase soil
erosion by wind and water which leads to desertification.

(b) Consequences
 Reduction in crops so as a result less food.
 Reduced total biomass, so less food for livestock.
 Reduced wood biomass, hence less wood for fuel.
 Reduced water availability, underground supplies increases
 Increase disruption to life, people need for relief aid increases leading
migration

(c)Conservation of soil
 Increase in terraced farming
 Increased contour ploughing
 Plant trees in line to check wind aped and to protect soil from wind
erosion.
 Use the system of mixed /inter cropping (plants between trees) to protect
them from being eroded by winds.
 Grow more grass around the crops to maintain surface cover and humus
of the soil.

Soil erosion: management strategies

The aim of soil conservation is the prevention of soil erosion so that the fertile topsoil retained.

(a)Mechanical method

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 The main strategy used for conservation in mountainous areas is terracing.

 Terracing built across slops hold the soil on flatter land. These are needed most in tropical
lands where most rain fall heavy storms. On a small scale there are bunds, for which stones
are placed across the lower ends of steep slopes to hold back soil and water.
 Contour ploughing (ploughing around or across the slope instead of up and down).
 Ridges formed by ploughing block the downward movement of water on slopes

(b) Changes in farming practices

Rates of erosion are low when the soil is covered, so following strategies are used

 Mixed cropping
 Crop rotation add organic matter
 Tree planting

Strategies for sustainable agriculture

Behind the concept of sustainable agriculture is the idea that we should not be putting
at risk tomorrow’s food supplies from the land because of today’s short term economic
greed. There are following six strategies helpful to sustainable agriculture.

 Use organic fertilizer

 Crop rotation
 Pest and drought resistant crop varieties
 Managing livestock grazing
 Trickle drip irrigation
 Rainwater harvesting

Past Papers Questions

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Q. What are the advantages of using legumes instead of fertilizer for the farmer
and for the ecosystem?

 Ans. legumes can be ploughed in after the crop to increase nutrients in the soil,
 legumes are a useful supply of beans/peas/animal fodder,
 legumes are less expensive/fertilizers are more expensive,
 danger to the environment of over-fertilization/legumes are more environmentally
friendly, eutrophication, leads to death of plants/fish,

Q. Describe the methods farmers could use to grow crops in dry climate.

 Ans. method of storage of water described
 channels / pipes bring water from storage
 sprinkler / other suitable method on terrace
 care needed not to over water / not to induce run off
 wells dug to tap into underground water supplies
 (ii) dry land farming
 widely spaced plants, no competition for small amount of water available
 mulch / straw etc. on surface, protects from evaporation
 protects from wind erosion
 grass strips between crops, reduce soil erosion explained
 GM drought resistant crops
 Plant seeds / crops after the rain
Q .Describe what has been done to allow farming to take place in hilly areas?

 Ans. terracing / land cut into steps

 flat areas
 across slope / parallel to contours
 narrow(er) on steep(er) slopes / wide(r) on gentle(r) slopes
 bunds / low walls at the edges
 (ii) steep slope
 (terrace) encourages / increases infiltration
 decreases run-off
 conserves soil / soil not washed down the slope (terrace or bund)
 contour ploughing so water sinks into furrows
 plough ridges prevent water from flowing downhill
 easier farming practices

Q. Describe the role of soil organisms in maintaining soils.

Ans.

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 decomposition; of (dead) plant material; of (dead) fauna);and turn them into

nutrients / humus /minerals; worms aerate the soil; move down / mix organic
material through the soil; role of organisms in: carbon cycle, nitrogen cycle, sulfur
cycle;

Q. Explain how fertilisers may damage the environment and suggest how their
environmental impacts can be reduced.
Ans.
 excess fertilisers washed into water courses leading to algal blooms and
eutrophication, with effects of plant and animal life in the water; controlled
application to limit excess fertilisers and possibly use of organic
fertilisers;clearance of algal blooms, oxygenation of water courses affected.
 OR
 provides detailed explanation of how fertilisers can damage the environment, but
nothing worthy of credit on reduction or vice versa

Q. Explain how the overuse and misuse of chemical fertilizers is harmful to

the environment.
 Ans. Pollution of rivers / groundwater
 With excess nitrates / phosphates
 Algae multiply rapidly
 On decomposition they reduce the oxygen in the water
 Eutrophication
 Plant / animal life in the water dies

Q. How could a farmer increase crop yields using alternatives to chemical

fertilisers?
Ans . use organic fertilizer / manure
 Use compost
 Mix farming
 Crop rotation
 Using nitrogen fixing plants eg using leguminous crops / peas / beans etc after
cereals

Q. What is meant by dry land farming?

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Ans. Farming in dry areas without irrigation

Q. Suggest reasons why farmers may prefer to use inorganic fertilisers rather
than organic ones.
Ans. Cheaper, easier to obtain, easier to apply lower mass, more pleasant / less smell
from them / quicker release, does not keep animals, does not wish to rotate / grow few
crops types, can target nutrients needed.
Q. State advantages of GM.
Ans.no competition with weeds, so better yields, only need to use one type of weed
killer
Q. Describe possible problems of having large areas of monoculture.
Ans. Loss of biodiversity, loss of insect pollinations, damage to soil, reduce fertility, soil
capping, soil pan formed
Q. Why do some people think that growing GM is a risk to environment?
Ans. Genes for resistance to roundup passed on to other species, by cross pollination,
loss of crop varieties
Q. Why does a scientist ask more than one person for collecting his data?
Ans. reliability, to calculate average / mean, for comparison, to give a more complete
picture.
Q. How the scientist would have made sure that the sample from all the site were
Comparable?
Ans. repeat the sampling, more time / stated time, repeat around another site.
Q. What is meant by rainwater harvesting?
Ans. This is trapping, collecting and storing rainwater which otherwise have been lost
as runoff down the drains or into streams.
.Q. State three environmental benefits of rainwater harvesting?
 Ans .
 Reducing runoff
 Decreasing the risk of floods and soil erosion
 Save the amount of water

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Q. Why can rainwater harvesting be described as an example of appropriate

technology?
ans. rainwater harvesting can be done by individuals or community groups
Q. Give a brief definition for each of the following:
(a) Organic fertilizer
Organic manure is known as Organic fertilizer
(b) Crop rotation
The main advantage of crop rotation is maintenance of soil fertility. If crops of different
sizes and periods of growth are planted in neighbouring fields.
(c) Managing grazing
Do not have too many animals for the amount of vegetation available
(d) Resistant crop varieties
Development of crop varieties that showed resistant from pests, herbicides and
diseases etc.

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