Limitations imposed by slope are taken into account in three steps. Step one defines the slopes which are permissible for fuelwood production, and as a model variable this is defined as slopes less than 45%.
Step two involves the computation of potential topsoil loss which is estimated, by input level, through a modified Universal Soil Loss Equation (Wischmeier and Smith 1978).
Step three relates the esti-mated topsoil losses to yield losses through a set of equations given in Table 9.1, taking into account soil susceptibility and level of inputs. The reduced impact under inter-mediate and high input levels is due to the compensating effect of fertilizer applications at their normal rates of use.
Steps two and three are described in detail in Technical Annex 1.2, and in greater detail in Mitchell (1986). Table 9.2 shows the soil units ranked in three classes according to their susceptibility to yield loss in relation to loss of topsoil, on the basis organic matter content, soil depth and on the presence of other unfavourable subsoil conditions.
In estimating yield losses from equations in Table 9.1 regeneration capacity of topsoil is taken into account in calculating net loss of topsoil. Regeneration capacities of topsoil by thermal and moisture regimes are given in Table 9.3.
