Factors Affecting Soil Erosion
Th major factor affecting soil erosion are climate, soil properties, topography, vegetation, animals, etc.
Precipitation (rainfall and snowfall), wind velocity, temperature and humidity are climatic factors that affect the soil erosion. Rainfall is the most forceful factor causing soil erosion through splash and surface runoff. In terms of temperature the climate is defined as tropical, sub-tropical. Temperate, cold temperate, arctic and sub-arctic. Erosion by water is quite serious in tropical and sub-tropical countries because of higher amounts of rainfall, whereas it is negligible in arctic regions. Strong winds in arid and semi-arid areas cause considerable soil loss through saltation, suspension and surface creep. Wind erosion causes dust storms, forms sand dunes and buries vegetation.
Soil properties largely depends upon texture, structure, organic matter, nature of clay and amounts and kinds of salt present in the soil. Generally, fine-textured soils are more subject to soil erosion. The soils able to retain more moisture to reduce runoff, therefore, are not erode easily. Coarser textured soil containing a greater proportion of sand can be removed by wind very easily.
Slope accelerates erosion as it increases the velocity of the flowering water. It has been observed that four time increase in the degree of slope doubles the velocity of flowing water and erosion by water therefore. Steepness also allows raindrop to hit the ground more directly causing erosion. Aspect of slope is also important in causing runoff and erosion. South slopes face sun directly and soil dries much more, therefore, eroded more easily. North facing soils are better covered with vegetation, therefore less subject to erosion. On nearly level land there is little runoff because much water is held as depression storage therefore less erosion.
The presence of vegetation acts as erosion-retarding factor. Forests and grasses provide better covet than cultivated crops. The vegetation intercepts the beating action of falling raindrops, retard the amount and velocity of surface runoff, permits more water flow into the soil and check abrasive power of wind. Plant roots and other residues of vegetation help to improve soil aggregation and porosity and thereby enhance infiltration and reduces runoff. Residue mulch prevents direct impact of raindrop on soil aggregates, maintains pore space and high infiltration rate and enhance crop growth to provide ground cover.
Animal traffic severely affects soil erosion. Large herds of cattle, buffaloes, sheep and goats taken out for grazing destroy vegetation cover through heavy grazing and by treading upon the soil with their hooves, therefore subject the soil to erosion. The footpaths used by humans and animals develop into rills (furrows) and then into gullies (deep trenches).
Mice, ants, earthworms, etc., also induce erosion. The castings formed by earthworms are washed away during heavy rains. The microorganisms such as protozoans, bacteria, fungi and algae affect the decomposition of organic matter affecting’ the soil erosion.
Tillage is also an erosion-inducing factor in agriculture as it detaches the soil and tends to oxidize its organic matter. Continuous ploughing to the same depth leads to the development of a plough pan which reduces infiltration capacity and consequently higher runoff and erosion.
Glaciers also cause considerable erosion at higher altitudes and Iceep on advancing year during winter months. They cause soil failure, destroy vegetation and expose the soil surface to direct action of raindrops during summer when the snow cover is cleared of due to high temperature.
Effects of Soil Erosion (Losses Caused by soil Erosion)
Soil erosion is a worldwide problem It results in landslides in hilly areas, floods in destruction of agriculture land, Silting of reservoirs, etc. Therefore, soil erosion is detrimental to the economy. Some of the effects of erosion are as followings:
Loss of Soil
The eroded soil particles are carried in suspensions by water or wind from a few centimeters to hundreds of kilometers. When these particles sediment they cover the soil with a thick layer of coarse soil and stones which is damaging. Also accelerated sedimentation gives no time for soil development. However, deposition of a thin layer of finer soil material improves soil fertility. It has been estimated that the loss of soil by erosion on unprotected land is often as much as 50 tons/acres/year and may go up to 120 tons/acre/year.
Change of Soil Texture
Water erosion washes sand, silt and clay particles of topsoil along with organic matter and other cementing agents, and deposits (sediments) these in depressions or at the bottom of the slope from where these particles may be carried to other places. This results in separation of soil particles of top soil which has more desirable structure. The change in soil texture results in loss of soil fertility affecting the productivity and moisture retaining ability of the eroded soil.
Loss of Nutrients
Erosion causes tremendous loss of essential nutrients such as P, K, N2, Ca and Mg. It is estimated that bare cultivated lands may lose organic carbon, nitrogen, available P205, available K20, exchangeable Ca and Mg up to the tune of 103.3 kg/ha. Removal of nutrients affects soil fertility and productivity of the soil.
Silting up of Reservoirs
Suspended silt., clay and organic matter is carried by water to the reservoirs and sediment to the lower end of the reservoirs causing silting up of reservoirs (silt makes up more than half of the suspended material therefore the entire deposit is given the name of silt). Silting up affects the water supply, the energy projects, etc.
Increase in the rate ‘of erosion beyond normal, erosion results in increased Sedimentation and quick built up of the river bed reducing the capacity of stream to carry the increased run off. This leads to flow of water over the banks, flooding the low lands, Flooding causes deforestation, damage to crop land and formation of ravines and gullies in the catchment areas.
Loss of Crops
Runoff water or blowing soil causes crop damage. Under extreme conditions crops may be completely destroyed, Removal of top soil results in decline of productivity of the land. In arid and semi-arid regions drifting soil result in burying of grass, trees, shrubs and hedges. The moving soil may also carry insects and weed seeds to clean fields.