Topic 3 Flashcards
Soil composition
Mineral particles: combination of rock fragments and other inorganic substances. They are formed due to physical, chemical, and biological weathering of the parent rock.
Organic content: mixture of living plants, animals, microorganisms and their dead remains.
Air: held within the pore spaces (between the mineral particles and organic content). Air enters the soil by diffusion.
Water: held within the pore spaces (water that is available for plant growth). Water enters the soil when there’s precipitation or when the soil is irrigated.
Types of soil
Sand
2.0-0.02 mm
Gritty
Silt
0.02-0.002 mm
Silky or soapy.
Clay
<0.002 mm
• Sticky when wet.
Hard when dried.
Mineral ions
Mineral Ions:
Plants require a supply of nitrogen, phosphorus, potassium (NPK) and a range of other elements to construct proteins and carry out life processes which are provided usually by fertilizers.
Use of fertilizers: increase the rate of growth of crops.
Nitrogen V
Phosphorus
Potassium
Element
Supplied as
Nitrate ions (NO3)
Phosphate ions (PO43)
Potassium ions (K)
Importance of organic matter
-Increase the water-holding capacity (like a sponge).
-Increase air spaces in the soil providing additional drainage and less compaction.
-Increase number of decomposers in the soil.
-Prevent the loss of mineral nutrients.
-Reduces soil erosion as organic matter acts like a base to smaller particles which hold soil
together.
Organic content
Organic content (animal manure and fertilizers):
Decomposers that produce humus (rich in nutrients):
Earthworms: break down vegetation; mix the soil; aerate the soil; spread organic matter through the soil.
o Fungi: feed directly on dead matter.
o Bacteria: work on organic matter; convert waste products to simple chemicals; some convert nitrogen to nitrates which is important in nitrogen cycle.
Increasing agricultural yield:
Crop rotation: the principle of growing different types of plants in different plots each y
• Legumes: have nitrogen-fixing bacteria in their root nodules.
year
o Leafy crops: vegetables that are required for their leaves (require a lot of nitrogen usually
left by legumes).
о Root crops: have deep root systems.
Advantages of crop rotation:
Diseases in the soil affecting the plant are left behind.
Spi Cody dives
Pests need to find a new site, so their population is reduced I post Papal
The soil in the new plot is likely to have the essential nutrients. Crops ready to harvest at different times so less potential waste.
Fertilizers: contain minerals such as nitrogen, potassium, and phosphorus (NPK) which
increase the rate of growth.
Organic
Advantages
Uses natural resources.
Supplies organic matter.
Cheap.
Disadvantage
Unpleasant to handle. Harder to transport.
Variable in composition.
Inorganic
Meet a particular need.
Easier to store.
Disadvantages
Expensive.
Slow acting
No need to reapply.
Disadvantage
Little immediate impact.
Quick acting
Deficiency problems are solved quickly. Easily leached out in heavy rain.
Irrigation:
Supplying water to the crops.
о Large percentage of a plant is made up of water.
Essential for cell activity.
Used in photosynthesis.
Mineral nutrient uptake requires water in the soil.
> Common water application methods:
Overhead Sprinklers
Advantages
Easy to setup.
Can cover a large area.
Disadvantages
Large droplets may cap the soil.
Small droplets may be blown away by wind.
Water lands on leaves and soil, which
evaporates quickly.
Clay Pot Irrigation system
Advantages
Easy to check the amount of water.
Simple technology.
Disadvantages
Only suitable for permanent plants.
Large labour cost.
•
Trickle Drip irrigation System
Advantages
Automated and well controlled.
Constant flow of water so soil does not dry out.
Avoids waterlogging so reduces risk of salinization.
Less water used so reduces risk of
leaching and minimises water loss.
Water placed directly at the roots of the plant so only crop plants receive water.
Disadvantages
Expensive to install; complex to maintain
Grit can block tubes, so a filter is Inflexible; cannot be moved easily
.
Flood Irrigation
Advantages
Inexpensive.
Can cover large areas quickly.
Disadvantages
Inefficient use of water.
• Damages soil structure.
• Salinization.
Pest control (insects, weed and fungi)
> Pest: an (animal, insect, fungi) that attacks or feeds upon a crop plant.
> Pesticide: used to kill pests (insects, plant diseases, fungi).
Insect control by:
Insecticides: insect-controlling chemicals are called insecticides.
o Biological Control: find natural predators.
Advantages
No chemical residues.
No impact of sprays.
No need of Reapplying
Disadvantages
Not as instant as chemical control.
Pests may breed faster than the predator.
Predator may feed on an unintended plant.
The predators will die naturally when the pests are controlled.
Weed control by:
o Herbicides: weed-killing chemicals are known as herbicides.
Weed must be controlled because:
1. Compete with crops for light, water and nutrients.
2. Might be poisonous.
3. Make cultivation difficult.
4. Can block drainage systems with excessive growth.
5. Can be a source of pests and diseases.
6. Can look untidy (impact on tourism areas).
Advantages of herbicides:
1. Easy to manage.
2. Cheap.
3. Results are predictable.
4. Effect is rapid.
5. Alternatives may be less effective.
o Alternatives to herbicides are cultural controls:
1. Hand weeding.
2. Weed barriers.
Fungi control by:
o Fungicides: fungal diseases are common and controlled by fungicides
Mechanization:
o Larger area can be cultivated.
Reduces labor cost.
o Ploughing can be done even when soil is heavy.
Selective breeding:
1. Choose parents that exhibit the desired characteristics of the species.
2. Raise the offspring from these parents.
3. Select the best offspring that shows the desired characteristics.
4. Repeat the process.
o Examples: cattle, wheat, and rice.
Drawbacks: slow process; less success rate.
o Characteristics: pest-resistant, drought-resistant, disease-resistant, size
Genetically Modified Organisms (GMO): the DNA of one organism is
then inserted into another.
Advantages
Higher yield from lower inputs.
Less area needed to produce a crop.
. Crops can be made with longer storage lives
• Crops can be made resistant to drought and salinity
The organism’s disease resistance and insect resistance may increase, which result in less use of insecticides which impacts the environment and less money spent on herbicides.
Crops can look more appealing.
·
Disadvantages
extracted
Risk of GM characteristics such as herbici resistance getting into other plants (super weeds) so results in more herbicide use on resistant crops which have toxic effect on ecosystem.
· Genes might get into wild plants if they interbreed with GMOs so reducing biodiversity.
Products are not natural so unknown impact of the new characteristics on human health and environment may occur.
Reduction in the gene pool.
Controlled environments:
Greenhouse/ glasshouse: a controlled environment so optimum conditions can be provided.
> Optimum temperature and carbon dioxide increase rate of photosynthesis.
> Optimum water supply, nutrients and pest control is essential for plant growth.
Growth Factor
How to Increase
Operate heating system
(e.g., insulation).
Temperature
Light Humidity Water
Artificial lighting.
Heat management.
Sprinkler or irrigation.
How to Decrease
Open roof ventilators.
Shading material in the roof.
Open roof ventilators.
m
Drainage material underneath.
o Hydroponics: growing plants without soil, with the nutrients the plant needs dissolved
in water.
Advantages
No need for soil.
Can be used anywhere.
Easy to harvest.
Exact nutrients needed are provided.
Water is recycled.
Reduce the number of pests.
Disadvantages
Expensive to set up.
Suitable for small production areas.
Technical knowledge required.
Disease, if present, may spread rapidly.
Plants can die quickly if conditions are not maintained.
Types of agriculture
Subsistence
Cultivation of crops to provide enough food for farmers and families
It is practiced on small patches.
Primitive tools are used.
Production is low.
Examples: wheat and rice.
NB: encourages self-sufficiency and reduces migration to urban areas.
them for cash (cash crops).
Commercial
Cultivation of crops with the main aim of selling
It is practiced on a large scale.
Modern technology is used.
Production is high.
Examples: tea, coffee, cocoa, sugarcane, cotton. NB: some cash crops can’t be used as food, risk of crop failure causes loss of income.
Arable Production of plants for consumption by humans
Examples: rice, wheat, maize and soybeans.
pastoral Production of animals or animal-related products.
Examples: grass/grain to feed the animals that produce milk, wool and eggs.
Mixed
Farms that grow crops for food and rear animals.
Impact of agriculture
• Overuse of herbicides and insecticides:
。 Food web is disturbed, and biodiversity is decreased.
O Unintended environmental damage: beneficial insects in pollination like bees are affected.
o Other animals eat poisoned insects and die.
Can cause resistance within the pest population, increasing number of pests.
Run-off into rivers causes water contamination
o Toxic effect on marine life (bioaccumulation).
o Over-use of pesticides causes air pollution.
о Can remain in the environment for generations. Example of dangerous pesticides: DDT
• Overuse of fertilizers:
o Excess water containing dissolved fertilizers leach to lakes and rivers, leading into nearby eutrophication, which causes increase of algae growth (algal bloom), so sunlight is blocked, and photosynthesis is reduced, this causes the algae to die and causes increase in bacterial count to decompose the dead algae. This bacterial increase uses up oxygen. So, aquatic organisms die due to the lack of oxygen.
o The addition of extra mineral nutrients is a waste of money and resources if the soil has
reached its maximum level.
Nitrates from fertilizers if consumed can cause diseases such as blue-baby syndrome
o Large quantities can affect the pH of the soil and the availability of minerals. o Too much fertilizers dehydrates the plant (scorching).
Mismanagement of irrigation causing salinization and waterlogging:
Death of plant roots because waterlogged soils prevent plant roots from getting enough
Salts are toxic so land becomes unusable and lower crop yield is produced.
Damage to soil structure as soil is compacted.
Loss of nutrients as they are dissolved and leached with water.
Run off increases soil erosion.
Salinization: salt content of soil increases so plants are not able to uptake water from the soil.
- Irrigation water soaks into the soil to a great depth.
- Salts dissolve in the water at a great depth.
- Water evaporates from the field.
- Water and salts are drawn up to the surface.
- Salt remains at the surface and kills plant roots.
> Prevents soil cultivation as it’s difficult to cultivate soil with high-water content. - Overproduction and waste:
o Waste from overproduction: the unsold proportion of the crop.
Waste of storage space.
Waste of transportation: to sell a crop, a farmer may need to travel longer distances.
o Waste of labor: inefficient use of time and labor if too much is produced.
• Exhaustion of mineral ion content:
o The farmers use the soil repeatedly with little or no rest, which leaves the soil depleted of nutrients and minerals.
o Solution: crop rotation, mixed cropping and leaving the land fallow.
o Fallow: the land is ploughed but left barren for a period to restore soil fertility and to avoid surplus production.
• Soil erosion:
o Over-cultivation: soils that are cultivated regularly lose soil structure and are more
vulnerable to erosion as they break down to smaller particles.
• Cash crops replacing food crops:
o Most commercial farmers prefer to grow crops that generate more cash. This causes a decline in the staple food available.
Cause of soil erosion
• Causes of soil erosion:
1. Removal of natural vegetation:
。 No interception which is Precipitation that does not reach the soil but is instead intercepted by the leaves and Soil and branches of plant
happens to the precipitation.
o No more roots to bind the soil together or slow down the torrents of water.
The infiltration which is the process by which precipitation/water soaks into soil. decreases, so flash flooding and surface run-off pick the soil and carry
it away.
Removal of natural vegetation is due to increase in population which increases demand for food
causing:
A- Overcultivation:
Ploughing breaks the soil into smaller and lighter particles. These are more easily rear carried away by wind.
B-Overgrazing:
livestock reduces the vegetation to nearly ground
boost level, sometimes leaving no roots to hold the soil.
• Animals trample down the plants and their hoofs
compact the ground.
C-Urbanization and increased demand for wood
2. Wind erosion:
1- Deforestation due to excessive grazing, increase in development of arable crops
2- Soil is dried by sun which increases the chance of soil getting eroded by wind.
- Water erosion: heavy rainfall carries the particles away.
On a slope, excess run-off water that can’t be absorbed by soil
transports the soil from that area.
Soil compaction reduces infiltration.
Gully erosion (volume of water erodes local soil further) forms
deeper and deeper cracks (landslide).
Impact of soil erosion
Impacts of soil erosion:
Loss of habitat:
Organisms living in the topsoil lose their habitat which impacts the entire ecosystem so less biodiversity.
o Desertification:
The process by which fertile land becomes desert.
o Silting of rivers:
Flooding occurs as water bodies can’t hold excess water (space taken up by silt).
Silt affects the quality and availability of water for drinking.
Aquatic organisms are buried under the silty layer: preventing light from reaching the underwater plants (low oxygen levels in ecosystem so no photosynthesis).
o Displacement of people
• which is breeding ground for female Anopheles mosquito Causing malaria
Severe soil erosion may lead to migration of the whole community.
o Malnutrition and famine
crops
Loss of farmland leads to risk of famine and malnutrition and have negative economic impact on the farmers.
How to improve agriculture
3.8 Sustainable agriculture
Aims of sustainable agriculture:
o Meeting the needs of the population for agricultural products.
。 Making efficient use of non-renewable resources.
o Supporting the natural ecosystem by following natural processes with farming techniques..
o Sustaining the economic independence of farmers.
Organic fertilizers (crop residue, manure)
Field residues are materials left in an agricultural field after the crop has been harvested. Manure is used as organic fertilizer in agriculture. Most manure consists of animal faeces.
o Improve soil structure
o Are slow acting so reduces the risk of eutrophication.
Are a waste product so using them saves on disposal costs.
o Are already present in many farms so minimal transport costs.
o Do not require energy for their manufacture.
Managed grazing(livestock):
o Prevention of overgrazing to prevent compaction of the soil.
o Ensure sufficient grazing to maintain appropriate soil fertility by animal waste.
Animals can feed over crops.
Crop rotation
Use of pest and drought resistant varieties of crops:
o reduce pesticide use and reduce water usage for irrigation
Trickle drip irrigation:
o allows less water to be used Rainwater harvesting:
o the collection of rainwater and its storage in a tank or reservoir for later use
Strategies to reduce soil erosion
Strategies to reduce soil erosion:
Terracing:
Prevents the erosion of soil by water run-off on steep slopes.
o In a natural slope: water runs down, increasing in speed and volume, carrying soil in the run-off.
o In a terraced slope: Land is cut into flat surfaces and then into levels, so it reduces the slope.
The speed of the surface run-off is reduced as soil is held back by terraces and water is held back by bunds.
E.g., Often used for cultivation of rice.
Advantages:
1. Increase area for farming.
2. Easier to work when land is flat.
- Fertilizers don’t run away.
Contour ploughing:
Reduces run-off down a slope.
Ploughing of land along the contour in a parallel way. o Ridges and troughs (furrows) run along the
contour.
o Each furrow holds water and prevents large
torrents of water running down the slope, preventing the formation of gullies and run-off of topsoil.
Bunds:
Artificial banks at the edges of growing spaces built along contour lines by raising up the soil. Used to hold back water, slow down and collect the surface run-off of water to reduce water erosion and increase time for infiltration and reduces wind speed to reused wind erosion.
Useful for crops that require moist soils e.g., rice.
O The water is retained on the terrace (like terracing).
Disadvantages:
Hard physical work
o Time consuming
O Needs to be maintained
Windbreaks:
A permeable barrier used to reduce loss of soil due to wind on an area.
o Without windbreaks, the soil is eroded away.
o Solid structures, like walls, force the wind into smaller spaces, increasing wind speed.
O Permeable structures, like vegetation, allow some wind to pass through, decreasing its speed and thus, the amount of wind erosion.
Advantages:
1.,additional habitats for beneficial insects
2. roots of the windbreak prevent erosion due to run-off
• Maintaining vegetation cover:
o Sowing legumes immediately after a crop has been harvested prevents soil erosion.
o It also provides more nitrogen to the soil, increasing its fertility, for the next major crop.
o When cultivating, the legumes can be simply ploughed.
• Addition of organic matter to improve soil structure
• Planting trees:
Roots bind the soil particles which prevents the soil from being blown away by wind. Tree leaves increase rainfall interception so the rainfall reaches the ground more slow
so less erosion will occur due to less surface run-off.
Increases infiltration to reduce surface run-off.
Row of trees acts as windbreak.
o Tree canopy provides shade for shorter crops that do not need much sunlight. Provide a natural habitat for animals that feed on pests.
Tree leaves fall to the ground and add on to the organic matter (humus), which keep the
moisture in the soil and reduce weed growth.
Mixed cropping: growing more than one type of plant in the same area.
o Resources in the soil, like nutrients, are used more efficiently.
• Intercropping: rows of different crops are grown between the rows of the main crop so
different root depths that bind the soil together
Advantages:
1- Provide nutrients for the plants
2- Reduces soil erosion by roo
and infiltration
3- Less risk of crop failure as not dependent on one crop
4- More income
Crop rotation
