Plant materials for soil fertility management in subhumid tropical areas

Lantana camara L., Senna hirsuta (L,) Irwin &; Barneby, Tithonia diversifol ia (Hemsl.) A. Gray, and Aspilia kotschyi du Petit-Thouars occur naturally in eastern and central Uganda, Trimmings of these species were evaluated fo r effectiveness in improving soil productivity. The plant trimmings varied for N (13-30 g kg(-1)), P (1.1-1.8 g kg(-1)), Lignin (11-16%), and polyphen ol (1.3-2.5%) concentration. Decomposition rates were higher for incorporat ion than for surface placement, but placement did not affect maize (Zea may s L,) and bean (Phaseolus vulgaris L,) yield. Decomposition rates were simi lar for all species with the same placement method. Potassium and Mg were g enerally mineralized most and least rapidly, respectively, with intermediat e rates For N, P, and Ca. Maize and bean yield increased with application o f 4 Mg ha(-1) dry wt. trimmings of L. camara, S. hirsuta, and T, diversifol ia, but only maize eventually responded to A. kotschyi, Yields per units of N and P applied were more and less, respectively, with inorganic than with organic treatments, but plant trimmings supplied less P than fertilizer. A t the end of the trial period, available soil P was more for the full rate of Fertilizer than for the mean of the plant materials, Combining L. camara and fertilizer, at 50% rates, resulted in an average of 0.22 Mg ha(-1) mor e yield than expected from mere additive effects of the organic and inorgan ic resources, The value of plant materials may be enhanced by balancing nut rient supply with inorganic fertilizers.