Sources of nutrients for maize in nutrient-depleted soils of western Kenya

Maize yields are low and continue the decline in the densely populated highlands of western Kenya where the soils are deficient in nitrogen (N), phosphorus (P) and potassium (K) in some localities. Over the last seven years, a team of scientists from several agricultural and forestry research institutions (national and international), have been developing and testing onfarm several soil fertility replenishment technologies. Improved fallows of fast-growing leguminous species and biomass transfer from hedges on farm boundaries are two promising technologies. This paper examines the potentials and limitations of these two technologies. With improved fallows, maize yields can be more than doubled by a 6 to 18-months-old Sesbania sesban fallow compared to natural fallow and continuous cropping with no inputs. Improved fallows especially with Sesbania, are also economical with high returns to labour under conditions of high or increasing labour cost. Biomass transfer of fresh leaf material of Tithonia diversifolia from farm boundaries to cropped fields, can also be as effective in supplying N, P and K to maize as an equivalent amount of commercial NPK fertilizer. Tithonia is, however, more profitable with vegetables than maize because of the high labour costs of biomass transfer. While both improved fallows and biomass transfer can provide some P and increase availability of soil P, none of them can overcome the need for inorganic P input in P-deficient soils.