Crops and soil
Section 2
Overview
• This section focuses on soil and its role in
agriculture. Farming methods that degrade
soil and those that preserve or restore soil will
be contrasted. The section also explores
methods of pest control.
Content/Knowledge
Objectives
• Distinguish between traditional and modern
agricultural techniques.
• Describe fertile soil.
• Describe the need for soil conservation.
• Explain the benefits and environmental impacts
of pesticide use
• Explain what is involved in integrated pest
management.
Lab Activities
• Studying soil samples: soil’s color, texture,
moisture content, organic content and
consistency.
• Lab: Soil Texture and Permeability lab
(handout will be given)
Real-Life Connections
• Find soil survey information of your local area.
After studying, report on the soil conditions in
your area. What kind of crop do you think will
grow well in that particular area.
• Report your findings in the form of a journal.
Activity: World Farming Methods
• Choose a foreign country and then create an
online poster about its farming methods.
• Create a poster about the dominant types of
farming in your native land.
• You need to include information about crops
planted, farming equipment used, and
popular techniques used. Make sure you use
visuals to supplement any text. You may then
present it to the class
Quick Lab
Preventing Soil Erosion
1. Obtain three trays, and fill one with sod, (A section of
grass-covered surface soil held together by matted roots;
turf.), one with topsoil and one with a type of mulch, such
as hay.
2. Place each tray at an angle by creating a surface that
resembles a hill by using textbooks. Place a large bowl at
the bottom of the tray to catch the runoff.
3. Sprinkle 2 litres of water slowly to simulate heavy rainfall.
4. Use the scale to weigh the runoff of soil and water that
collected in each.
5. Analysis: which tray had the most soil erosion and water
runoff? Which had the least and why?
Agriculture: Traditional and Modern
• http://www.youtube.com/watch?v=-NhzhIMZng
Traditional Farming
• The basic processes of farming include plowing,
fertilization, irrigation, and pest control. Traditionally
plows are pushed by the farmer or pulled by livestock.
Plowing helps crops grow by mixing soil nutrients,
loosening soil particles, and uprooting weeds.
• Organic fertilizers, such as manure, are used to enrich the
soil so that plants grow strong and healthy.
• Fields are irrigated by water flowing through ditches.
• Weeds are removed by hand or machine. These
traditional techniques have been used since the earliest
days of farming, centuries before tractors and pesticides
were invented.
Modern methods of Agriculture
• Machinery powered by fossil fuels is used to
plow the soil and harvest crops. Synthetic
chemical fertilizers are now used instead of
manure and plant waste to fertilize soil.
• A variety of overhead sprinklers and drip
system may be used for irrigation and
synthetic chemicals are used to kill pests.
Fertile Soils
• Soil that can support the growth of healthy
plants is called fertile soil. Plant roots grow in
topsoil, the surface layer of soil, which is usually
richer in organic matter than the subsoil is.
Fertile topsoil is composed of living organisms,
rock particles, water, air, and organic matter,
such as dead or decomposing organisms.
• Most soil forms when rock is broken down into
smaller fragments by wind, water, and chemical
weathering.
• Most soil forms when rock is broken down into smaller
fragments by wind, water, and chemical weathering.
• Temperature changes and moisture causes rock to crack
and break apart, which creates smaller particles. The
seeds of plants can fall and take root on these soil
particles. It can take hundreds of years for these
geological processes to form a few centimeters of soil
• Fungi and bacteria live in the soil, and they decompose
dead plants as well as organic debris and add more
nutrients to the soil. Earthworms, insects, and other small
animals help plants grow by breaking up the soil and
allowing air and water into it.
Soil Horizon
• O) Organic matter: Litter layer of plant residues in relatively
undecomposed form.
• A) Surface soil: Layer of mineral soil with most organic matter
accumulation and soil life. This layer eluviates (is depleted of) iron, clay,
aluminum, organic compounds, and other soluble constituents. When
eluviation is pronounced, a lighter colored "E" subsurface soil horizon is
apparent at the base of the "A" horizon. A-horizons may also be the result
of a combination of soil bioturbation and surface processes that winnow
fine particles from biologically mounded topsoil. In this case, the Ahorizon is regarded as a "biomantle".
• B) Subsoil: This layer accumulates iron, clay, aluminum and organic
compounds, a process referred to as illuviation.
• C) Parent rock: Layer of large unbroken rocks. This layer may accumulate
the more soluble compounds .
Rhizobium
Soil Horizon
Soil Erosion: A Global Problem
• Erosion is the wearing away of rock or soil by
wind and water. In United States about half
of the original topsoil has been lost to soil
erosion in the past 200 years. Without topsoil
crops cannot be grown.
• Almost all farming methods increase soil
erosion.
Land Degradation
• Land degradation happens when human activity
or natural processes damage the land so that it
can no longer support the local ecosytem.
• In areas with dry climates, desertification can
result.
• Desertification is the process by which land in
and or semiarid areas become more desertlike
because of human activity or climatic changes.
• Read Desertification in Sahel region and share
your thoughts and understanding with your
partner. (Page number 386)
Dust Bowl
• As a result of the Soil Conservation Act passed
after the Dust Bowl events, U.S farmers are
more likely to use planting and grazing
techniques that protect the soil from erosion.
10 ways to Conserve Soil
• There are many ways of protecting and managing
topsoil and reducing erosion. Soil usually erodes
downhill , and many soil conservation methods are
designed to prevent downhill erosion
• Plant trees: We all know that the roots of trees firmly
hold on to the soil. As trees grow tall, they also keep
rooting deeper into the soil. As the roots of the trees
spread deep into the layers of soil, they contribute to
the prevention of soil erosion. Soil that is under a
vegetative cover has hardly any chance of getting
eroded as the vegetative cover acts as a wind barrier as
well.
Terraces
• Terracing is one of the very good methods of soil conservation. A terrace is
a leveled section of a hilly cultivated area. Owing to its unique structure, it
prevents the rapid surface runoff of water. Terracing gives the landmass a
stepped appearance thus slowing the easy washing down of the soil. Dry
stonewalling is a method used to create terraces in which stone structures
are created without using mortar for binding.
• No-till farming: When soil is prepared for farming by
ploughing it, the process is known as tiling. No-till
farming is a way of growing crops without disturbing it
through tillage. The process of tilling is beneficial in
mixing fertilizers in the soil, shaping it into rows and
preparing a surface for sowing. But the tilling activity
can lead to compaction of soil, loss of organic matter in
soil and the death of the organisms in soil. No-till
farming is a way to prevent the soil from being affected
by these adversities.
Can you think of the advantages and disadvantages of
no till farming?
No till farming
http://www.ipm.iastate.edu/ipm/icm/2006/5-15/notill.html
• Contour ploughing: This practice of farming across the slopes takes
into account the slope gradient and the elevation of soil across the
slope. It is the method of ploughing across the contour lines of a
slope. This method helps in slowing the water runoff and prevents
the soil from being washed away along the slope. Contour
ploughing also helps in the percolation of water into the soil.
Crop rotation: Some pathogens tend to build up in soil if the same
crops are cultivated consecutively. Continuous cultivation of the
same crop also leads to an imbalance in the fertility demands of the
soil. To prevent these adverse effects from taking place, crop
rotation is practiced. It is a method of growing a series of dissimilar
crops in an area sequentially. Crop rotation also helps in the
improvement of soil structure and fertility.
Contour plowing and Crop Rotation
• Water the soil: We water plants, we water the crops, but do we water the
soil? If the answer is negative, it is high time we adopt the method of
watering soil as a measure of conserving soil. Watering the soil along with
the plants is a way to prevent soil erosion caused by wind.
Salinity management: The salinity of soil that is caused by the excessive
accumulation of salts, has a negative effect on the metabolism of the
crops in soil. Salinity of soil is detrimental to the vegetative life in the soil.
The death of vegetation is bound to cause soil erosion. Hence, salinity
management is one of the indirect ways to conserve soil.
Soil organisms: Organisms like earthworms and others benefiting the soil
should be promoted. Earthworms, through aeration of soil, enhance the
availability of macronutrients in soil. They also enhance the porosity of
soil. The helpful organisms of soil promote its fertility and form an
element in the conservation of soil.
• Indigenous Crops: Planting of native crops is
known to be beneficial for soil conservation. If
non-native plants are grown, the fields should be
bordered by indigenous crops to prevent soil
erosion and achieve soil conservation.
• Use rotational grazing. There is a short grazing
period followed by a rest period of longer
duration. Grazing is done when the farm is still in
the vegetative stage. This prevents crops from
being totally eaten away.
Proper Soil Irrigation
• If topsoil is left dry at the surface, it becomes susceptible to
erosion by wind. Ensuring that the land is properly irrigated
at the surface can prevent this.
Build a Wind Barrier
• Although trees provide a partial wind barrier, sometimes
they are not enough. Building a barrier or fence at the edge
of a farm can stop a large portion of erosion due to wind.
Use Organic Mulch
• Using organic mulch for crops that are indigenous to the
region will maintain the correct soil temperature and
prevent erosion.
Test the Soil's pH Level
• Natural environmental hazards such as acid rain can
drastically change the pH level of large areas of soil.
Plant life is controlled to a certain extent by this pH
level. Maintaining the correct pH level in your soil is
vital for conservation.
Test the Salinity of the Soil
• Just like pH, improper levels of salt can have a negative
effect on the metabolism of the plants in the soil.
Excessive salinity levels will lead to the death of
vegetation, which causes erosion. Test the topsoil
annually to ensure it has the correct salinity.
Tips to Conserve soil erosion
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Use rotational grazing. There is a short grazing period followed by a rest period of longer duration.
Grazing is done when the farm is still in the vegetative stage. This prevents crops from being totally
eaten away.
Change the plant species on your farm. Don’t use tilling, instead use herbicides to kill the existing
plants.
Cover the entire soil with plants, which will significantly reduce erosion.
Along with the plants it’s important to water soil, which keeps it damp and makes it settle down.
Don’t cultivate soils on steep slopes. Do terrace farming.
You can construct wind barriers at the boundaries of the farm. This will prevent wind from blowing
away the soil.
Add humus to your soil. It will prevent soil erosion.
Keep grassed waterways to drain out storm water.
To fight storm water, use structures made of natural materials. Use logs or collection of large stones
instead of cement and concrete. Natural resources are more effective and inexpensive.
Plant strips of grass, trees or shrubs between water and cropland. It prevents surface movement of
fertilizers, pesticides and soil. Strips cause increased runoff of water into soil. There is increased
denitrification, in which microbes convert nitrate-nitrogen into gas form that dissipates to the
atmosphere. It decreases the amount of nitrate available to move into groundwater and surface
water supplies. They absorb nutrients, sediment, and pesticides moving from adjoining cropland
before they reach the water sources. The strip’s trees, grass or shrubs absorb the nutrients and
pesticides.
Enriching the Soil
• Soil was traditionally fertilized by adding organic
matter, such as manure and leaves, to the soil. As
organic matter decomposes, it adds nutrients to the
soil and improves the texture of the soil. But this has
been replaced by inorganic fertilizers to meet the
growing demand of food supply.
• If erosion occurs in areas where the soil has been
fertilized with inorganic chemicals, fertilizers and
pesticides may pollute waterways.
• A modern method of enhancing the soil is to use both
organic and inorganic fertilizers by adding compost
and chemical fertilizers to the soil.
Compost
• Compost is partly decomposed organic
material. Compost comes from many sources.
Many cities and industries compost yard
waste and crop wastes. This compost is sold to
farmers and gardeners, and the process is
saving costly landfill space.
Salinization
• The accumulation of salts in the soil is known
as salinization. It is a major problem in places
such as California and Arizona.
• Salinization can be slowed if irrigation canals
are lined to prevent water from seeping into
the soil, or if the soil is watered heavily to
wash out salts.
Reference
• Environmental Science By Karen Arms