Per capita agricultural production and crop yields per unit area of production in Uganda,
like in other sub-Saharan African countries, is declining (IBSRAM 1994; Sanchez et al.
1996; FAO 1999). The main contributing biophysical factors are low inherent soil
fertility, particularly nitrogen (N) and phosphorus (P) deficiencies (Nye and Greenland,
1960; Ssali et al. 1986; Bekunda et al. 1997), exacerbated by nutrient/soil fertility
depletion (Vlek 1993; Sanchez et al. 1997a). In addition, a large number of the poorest
people in sub-Saharan Africa live in marginal areas where markedly increased land, and
labour productivity is unlikely (Vlek 1990).