Introduction to Soils
Soil is made up of loose, weathered rock and organic material which serves as a natural medium for the growth of land plants. The rock material in soil consists of sand, clay and silt. It is an essential part of the terrestrial ecosystem.
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Soil Formation
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Soil is formed over time from a combination of five soil-forming factors. These include parent material, climate, topography, biological organisms and time. Parent material is the starting material for a soil which consists of specific minerals.
Temperature changes, precipitation and wind break down parent material and transport loose particles thereby affecting the formation of soil.
Topography, or the location of a soil, also affects soil formation. Because of differences in elevation and slope, soils at the hillside and at the bottom of the hill receive varying amounts of water and sunlight. Thus, the soil on the hillside is drier.
Biological organisms control the decomposition of waste materials in the soil. They are also responsible for carbon dioxide, nitrogen and oxygen exchange between soil and the atmosphere.
Soil Profile
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Soil profile is the cross section of earth exposed by digging. There are three distinct zones or horizons (A, B and C) in a soil profile. Beneath this is the parent material. The A-horizon is topsoil which is darker than soil in other horizons as it has humus or organic material. The B-horizon begins with the subsoil. The color is usually red or brown because of the iron-oxides that were formed in the A-horizon and washed down. The B-horizon also contains clay. The C-horizon contains slightly weathered parent material such as rock fragments.
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Soil Texture
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According to the Mississippi State University, soil texture is the content of sand, silt, clay and organic matter of a particular soil. The texture affects water-holding capacity, the structure of the soil, the consistency of the soil, the capacity of the soil to hold nutrients and the ease of cultivation.
Soil Types
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Tropical soil: This soil forms in areas that experience constant high temperatures and heavy rainfall. The warm and wet conditions expedite the weathering process and this leads to quick soil formation. These soils are relatively infertile as heavy rains wash the nutrients out of the soil.
Grassland soils: These soils form in areas that receive enough rainfall for heavy grass, but not enough for trees. Grassland soils are rich in organic matter resulting in very fertile soils.
Forest soils: Forest soils form in humid regions that experience cool seasons. Hardwood and evergreen trees grow in these soils, which are not that fertile.
Desert soils: These soils form in very dry climates. Nutrients can be washed from the soil in wet climate settle in this soil. When watered, these soils can be very fertile.
Arctic soils: Arctic soils form at high elevations and high latitudes. The surfaces of these soils are inadequately drained and the bottom layers are permanently frozen.
Soil Conservation
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The removal of topsoil by the action of water or wind is known as soil erosion. It can be reduced by a number of methods of soil conservation. These include the planting of windbreaks or belts of trees along the edges of fields which reduce soil erosion from wind. Another method is contour farming, in which crops are planted in rows parallel to land contours, instead of plowing up and down a hillslope. This measure prevents water from rapidly flowing downhill and carrying soil with it.
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