Effects of biological techniques in soil conservation and subsoil inorganic-N accumulation in the central highlands of Kenya

Abstract

Soil erosion and nutrient leaching are some of the factors hindering realization of full crop production potential in the central highlands of Kenya. A participatory trial involving use of calliandra, leucaena, napier, leucaena + napier and calliandra + napier contour hedges was started in farmers' fields . of central highlands of Kenya in September 2001 to evaluate the effectiveness of hedges in soil conservation and nutrient cycling. At the start of the trial there was a substantial accumulation of inorganic N with depth. Twenty months later, leucaena,' calliandra, and leucaena + napier substantially depleted the subsoil inorganic N by more than 50%. On the other hand napier decreased mineral-N leaching slightly and showed a small bulge beyond 30-90 cm depth. Treatments on 10-20 % slope category registered a higher average soil loss compared to others on 5-10, 10-20, 20-30 and30 % slope categories. There was soil loss of up to 140 t ha-' on the control at 10¬20% slope category over the study period and a reduction of up 78% of this by sole napier (Pennisetum purporeum) hedge. The overall efficiency of the hedges in soil erosion control followed the order: napier calliandra + napier leucaena + napier calliandra leucaena control.