Tithonia and senna green manures and inorganic fertilizers as phosphorus sources for maize in Western Kenya

Efforts to overcome declining soil fertility on small holder farms in weste rn Kenya must be consistent with the reality of low utilization of inorgani c fertilizers. Likewise organic inputs alone cannot supply adequate nutrien ts. The use of two organic resources, Tithonia diversifolia (tithonia) and Senna spectabilis (senna) leaves, and their combination with inorganic P fo r improving soil fertility and maize yields was investigated on a P limitin g soil in Western Kenya. Treatments included: 1) control, no inputs; 2) 5 t ha(-1) (dry matter) tithonia leaves; 3) 5 t ha(-1) senna leaves; 4) 5 t ha (-1) tithonia leaves + 25 kg P ha(-1) as triple superphosphate (TSP); 5) 5 t ha(-1) senna leaves + 25 kg P ha(-1) (as TSP); and 6) 25 kg P ha(-1) of T SP. Maize was used as a test crop. Decomposition and P and N release of tit honia and senna leaves were determined in a litterbag study. Tithonia + TSP applications tripled maize yields compared to the control, senna + TSP and tithonia sole application doubled yields, while senna sole applications di d not increase yields substantially. A large residual yield was produced in the tithonia treatments in a subsequent crop. These yield results were con sistent with the higher quality and faster release of N and P from the tith onia leaves compared to senna. The tithonia biomass transfer system can imp rove yields in the short term but has limitations because of the large amou nt of biomass and the associated labor requirements.