What is soil conservation?
Soil conservation is the protection of soil from becoming irreversibly altered, and consequently infertile and vulnerable to erosion. There are two main approaches to soil conservation: the first is to halt the procession of chemical alteration and erosion, and the second is to try to reverse or reduce their effects.
Methods of preventing physical soil erosion
Cover crops can be used to aid many aspects of sustainable agriculture, from pest control to soil fertility and quality. This method has been subject to much research due to the ability of cover crops to replace or maintain levels of nitrate in the soil; nitrate is often the main limiting factor in crop growth.
Leguminous plants are often used as they are able to fix biologically unavailable nitrogen gas from the atmosphere into the biologically available nutrient nitrate; this is through their symbiotic relationship with rhizobial bacteria residing in the soil. This provides an alternative to using chemical fertilisers, produced through industrial nitrogen fixation (the Haber-Bosch process). This industrial fixation method has been widely criticised, as it relies heavily on fossil fuels to generate energy for fixation. Chemical fertilisers produced through industrial nitrogen fixation also have wide-ranging environmental impacts; one of the greatest problems with heavy use of chemical fertilisers is the leaching of nitrates from the soil; these nitrates run into waterways and cause eutrophication (overgrowth of waterway weed due to high availability of nitrate). Hypoxia quickly ensues, which can produce a dead waterway as organisms suffer from lack of oxygen.
Catch crops can be used to prevent this leaching process; they store excess nitrate from fertiliser and recycle nitrogen already present in the soil to prevent loss of nitrate through leaching or volatisation to nitrogen gas.
Cover crops may also add to the organic matter (humus) of the soil as the plants die and decompose. Humus increases the water capacity of the soil and therefore further prevents leaching and soil erosion. Planting cover crops and crop in alternate rows can allow protect against erosion of soil through wind.
Besides issues of soil conservation, cycles of disease may be broken through the addition of cover crops, and they can also attract pests away from the crop if they offer a more favourable habitat.
These are often trees, shrubs, or hedgerows, which offer some protection from the wind. Wind can remove the top layer of soil if the ground has become dry; therefore planting a windbreak can prvent this form of soil erosion.
These are often needed on bare soil sites, such as construction sites, where planting is not a feasible solution. Preventing surface run-off through the use of plastic-wrapped hay bales is one method, and mulching of soil surfaces can also be applied.
There are other methods of mechanical soil erosion prevention that have been in use for centuries; these include terracing, and contour farming. Contour farming is where land is ploughed following the lines of topographical elevation. This reduces the speed of surface water run-off and therefore soil erosion. Contour bunding may also be used; here stones are placed along the contour lines of the land.
Terracing is the levelling of sections of ground on a steep incline to provide usable land where a slope may have presented difficulties. The terracing also reduces the flow of surface run-off.
Methods of preventing chemical change within the soil
Salinisation is caused by the accumulation of salt ions in the soil; potassium, sodium, calcium, magnesium and chloride. Salinity in soil is an enormous problem; salt adversely affects the growth of most plants, leading to lack of vegetative cover and exposure of the soil to erosional forces. It is estimated that 33% of the world’s arable land has been affected by salinisation.
Salinisation can occur in two ways. When water infiltrates soil, salts are deposited in the upper layers of the earth. Therefore when land is over-irrigated, salts are deposited at an increased rate in the soil, leading to salinisation. Secondly, salinisation can occur if there is a shallow saline water-table; this was the case when the Aswan Dam was built in Egypt in the 1970s, leading to enormous loss of arable land due to salinisation as the water table rose.
There are two approaches to reversing salinisation. A salt-tolerant cover crop can be grown until the soil recovers enough to crop arable crops; the North American saltbush can be used for this purpose. Alternatively, humic acid may be added to the soil; this binds and removes anions and cations from the root zone of plants. This method is particularly effective in those areas where salinisation has arised as a consequence of excessive irrigation.
Soil pH may be altered by acid rainfall, produced as a result of sulphurous emissions from industrial areas. pH affects the nutrient uptake of plants; a low pH can aid uptake of nutrients but can cause large fluctuations in their availability. Different crops grow optimally in different pH of soils. Soil pH can be raised through the addition of lime.
Soil organisms are vital to the maintenance of healthy soil; these may be microorganisms such as rhizobial bacteria, or macroorganisms such as the earthworm, or fungi. Earthworms produce casts which are high in nitrate, and burrow through the soil to aerate it and form pores. Mycorrhizae increase the uptake of nutrients, water and minerals for vascular plants; these are symbiotic relationships in which microscopic fungi associate with the roots of vascular plants. Slash and burn farming is extremely detrimental to the diversity of organisms found within a soil, and excessive slash and burn agriculture may lead to irreversible damage to the soil.
This is the addition of substances such as crushed rock to the soil in order to increase the availability of a wide variety of minerals within the soil.
Soil conservation is central to maintaining food production levels. As the world’s population expands, environmental issues such come to the foreground as sustainability becomes vital to maintaining current and necessary levels of food production, rather than a desired ideal for agriculture.
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