Soil Erosion

soil, erosion

Soil erosion is the carrying away of soil by wind or water. Over long periods of time, usually thousands of years, it makes definite changes in the earth is surrface. The chief factors which cause water erosion are: .
1) the amount of cover given to the soil (erosion is slow where soil is covered by trees or grass),.
2) the amount and intensity of the rainfall and its distribution during the season (hard rains can cause most of the soil loss),.
3) slope is also a very important factor — the longer the slope, the more the soil and water are lost when the soil is cultivated, 4) the nature of the soil affects the amount of soil loss. The topsoil is usually the most valuable part of the soil profile because it contains more plant, food and organic matter. The surface soil can absorb water much quicker than subsoil. As the surface layer becomes thinner, less water soaks into the soil and more runs off the surface thus increasing the rate of soil loss, 5) the reduction of organic matter causes a change in the structure of the soil, 6) tillage causes the rapid decomposition of the organic matter. Soil damage by wind erosion is serious and extensive, because it causes the crop damage or complete loss of crops. The main cause of water erosion is the lack of vegetative cover. This may be caused: .
1) by drought and high temperature which reduce growth of vegeta tion,.
2) by tillage, and growing of cultivated crops which give bad cover,.
3) the loss of grass in pastures. When soil is rather bare, freezing and thawing, wetting and drying loosens the surface soil and breaks down the soil aggregates to granules that can be easily picked up by wind. The most critical seasons are late winter and early spring, when the wind usually blows strongest, the land is covered with little vegetation and the soil is very liable to movement. Wind erosion is serious in arid and semiarid regions. The growth of grass is one of the simplest means for the protection of slopes against erosion by wind and by water rain action, When a good turf is formed, the grass will absorb most of the impact of rain drops and its roots will hold the soil in place. Special protection is necessary for the slopes close to the water line of canals, lakes or dams against erosion by wave action. It is done by means of rock riprap.