This article throws light upon the six main factors affecting soil erosion by water. The factors are: 1. Rainfall 2. Slope of the Land 3. Vegetation 4. Tillage 5. Nature of the Soil 6. Presence of High Water Table.
Factor # 1. Rainfall:
Precipitation is the most forceful factor causing soil erosion.
Raindrop impact exerts three important influences:
(a) It detaches soil;
(b) Its beating tends to destroy granulation; and
(c) Its splash, under certain conditions, affects an appreciable transportation of soil. Soil granules are loosened, detached and separated into fine particles by the action of dashing rain.
Dispersed soil particles are removed by run-off that causes erosion is dependent on amount, duration, intensity and frequency of the rainfall. The chance of soil erosion is greater where the rainfall is not only heavy but concentrated in short time rather than light showers distributed over a long period of time. In the latter case there is time available for the rain water to infiltrate into the soil. In former case, infiltration is very less, so that run-off (surface flow) is high which causes removal of soil.
Factor # 2. Slope of the Land:
Slope accelerates erosion as it increases the velocity of the flowing water. The steepness, length and shape of the slope all determine the amount of soil erosion. Of these three factors, steepness of slope is the most influential. In general, the greater the slope the greater the amount of soil erosion.
Factor # 3. Vegetation:
The type of vegetative cover and its condition aids in controlling water erosion in the following ways:
(a) Vegetative cover protects the soil from the beating and dispersing action of the raindrops by forming a canopy over the soil surface,
(b) Vegetation provides a mechanical obstruction to flowing water thus reducing their velocity and soil carrying capacity,
(c) The root helps in the building of better structure i.e., Sphere-like that increases infiltration and reduces a surface run-off, and
(d) Roots help in opening the soil and thereby aid in increasing water absorption and in reducing surface run-off.
Factor # 4. Tillage:
The infiltration and permeability of the soil is improved by the practice of proper tillage and thereby reducing the erosion. Soil erosion by running water is only possible when there is excess water over surface for free run-off. High infiltration and permeability results in rapid water absorption by the soil and hence, little run-off.
Factor # 5. Nature of the Soil:
Erodibility of soil is influenced by the nature of the soil, particularly its texture, structure, organic matter, amounts and kinds of salts present, presence of hard pan in the soil and sub-soil and presence of high water table.
In sands and other coarse-textured soils, high infiltration and permeability results in rapid water absorption and hence, in little erosion.Permeability in heavy soil is much low as compared to light soils and hence more soil erosion.
In fine-textured soils such as in clay loams, the structure is an important factor in determining erodibility. A soil with a granular structure, in which the fine particles are arranged in clusters or aggregates, absorbs water readily and is resistant to erosion.
(iii) Organic Matter:
It helps in formation of better and more stable aggregates and thus, in keeping the permeability high. When the organic matter decreases as a result of growing cultivated crops the erodibility of the soil increases.
(iv) Presence of Hard Pan (Layer):
Presence of hard pan in the soil or sub-soil checks downward movement by water thus, resulting into run-off.
Factor # 6. Presence of High Water Table:
Presence of high water table checks the infiltration and permeability thus resulting into more flow of water on the surface.