The Universal Soil Loss Equation

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Soil loss through erosion is influenced by a variety of factors. According to Morgan (2005), the factors controlling soil erosion are the erosivity of the eroding agent, the erodibility of the soil, the slope of the land and the nature of the plant cover. The eroding agent essentially refers to eroding forces such as water and wind. However, the current study focuses only on erosion by water, even though wind erosion is also significant. The above factors are also highlighted by Wischmeier and Smith (1978) and incorporated into the Universal Soil Loss Equation (USLE):
A = RKLSCP, (Equation 1) where A represents the computed soil loss per unit area, R is rainfall, K is soil erodibility, LS is slope length, C is vegetation cover and P …show more content…

(1997), soil erodibility is the average long-term soil and soil profile response to the erosive power of rainstorms. The soil erodibility is therefore a lumped parameter that represents an integrated average annual value of the total soil and soil profile reaction to a large number of erosion and hydrologic processes (Tingting et al, 2008). Erodibility defines the resistance of the soil to both detachment and transport. Although the resistance of soil to erosion depends in part on topographic position, slope steepness and the amount of disturbance, such as during tillage, the properties of the soil are the most important determinants (Tya & Oluwaseye, 2015). Erodibility varies with soil texture, aggregate stability, shear strength, infiltration capacity and organic and chemical content (Renard et al., 1997). Large particles are resistant to transport because of the greater force required to entrain them and fine particles are resistant to detachment because of their cohesiveness (Renard et al., 1997). The least resistant particles are silt and fine sands. Thus, soils with silt content above 40% are highly erodible (Richter and Negendank, 1977). Evans (1980) examined erodibility in terms of clay content, and found that soils with clay content between 9%–30% are the most susceptible to erosion. High soil erodibility is usually observed at lower elevations where soil structure, profiles are more defined and soils much deeper, this also assumes that …show more content…

The above ground components, such as leaves and stems, absorb some of the energy of falling raindrops, running water and wind, so that less is directed at the soil, whereas the below-ground components, comprising the root system, contribute to the mechanical strength of the soil (Morgan, 2005). Interdependency is therefore established between the vegetation cover, whereby the cover increases the soil resistance to erosion, which collectively is termed erodibility.
An experiment demonstrating the effect of vegetation cover known as the mosquito gauze experiment was conducted by Hudson and Jackson (1959). Soil loss was measured from two identical bare plots on a clay loam soil. Over one plot, a fine wire gauze was suspended, which had the effect of breaking up the force of the raindrops, absorbing their impact and allowing the water to fall to the ground from a low height as a fine spray; the mean annual soil loss over a ten year period was 126.6 t ha-1 for the open plot and 0.9 t ha-1 for the plot covered by gauze (Morgan, 2005). There is therefore a very significant effect of vegetation on lowering erosion rates. Figure 1.1 demonstrates the relationship between the soil loss ratio (SLR) and vegetation

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