Contribution of organic residues to soil phosphorus availability in the highlands of Western Kenya.

Abstract

AbstractThis paper provides a summary of the results obtained from selected field experiments conducted in western Kenya, which aims to: (i) identify organic residues to increase P availability; (ii) test the ability of organic residues to substitute for mineral fertilizers; and (iii) identify the best combinations of organic residues (Tithonia diversifolia) with fertilizers to improve P availability in soils and increase maize production. Selected characteristics of different organic inputs used as green manure (viz., Calliandra calothyrsus, Senna spectabilis, Croton megalocarpus, Lantana camara, Sesbania sesban and T. diversifolia) in a maize-based cropping system are also discussed. Results indicated that the soluble C:total P content of organic residues was an important parameter in the selection of residues for improving soil-P fertility. In low input and P-deficient systems, organic residues can replace fertilizers and a greater benefit can be obtained from organic residues with small soluble C:total P ratio's, such as Tithonia, Croton and Lantana. However the limited supply of these organic inputs and the need for P replenishment encourages the use of a combination of organic and inorganic P sources, the best option being the maximization of the amount of P supplied by organic residues.