The methodology for the estimation of topsoil loss is essentially based on the Universal Soil Loss Equation (USLE): Wischmeier and Smith 1978). The topsoil loss is subsequently converted into productivity loss with or without specific soil conservation measures. The methodology is schematically shown in Figure 2.1, and comprises of the following steps:
Identification of land utilization types (LUTs), as defined for crop, livestock and fuelwood productivity models.
Determination of (USLE) factors for soil erosion: i.e. rainfall erosivity factor, soil erodibility factor, vegetation/crop cover factor, management factor and physical protection factor.
Application of USLE to quantify (LUT-specific) topsoil loss.
Establishing the relationships (equations) between loss of yield and loss of topsoil, and classifying soil units according to their susceptibility of yield loss due to loss of topsoil.
Application of equations from (iv) to estimate productivity loss in relation to productivity potentials as quantified by the land use (crop, livestock, fuelwood) productivity models.
Derivation of productivity estimates, tolerable soil loss and costs for alternative conservation measures.
FIGURE 3.1
Make-up of land resources data base
