Effects of combining organic materials with inorganic phosphorus sources on maize yield and financial benefits in western Kenya

Abstract

Due to escalating costs of imported fertilizers, there is renewed interest in the use of local nutrient resources in managing soil fertility in Kenya. We tested the effect of two organic materials, farmyard manure (FYM) and Tithonia diversifolia (tithonia), and an inorganic N fertilizer, urea, when applied alone or in combination with three inorganic P sources, triple superphosphate (TSP), Minjingu phosphate rock (MPR) and Busumbu phosphate rock (BPR), on maize yields and financial benefits. The study was conducted for three consecutive seasons, from March 2007 to August 2008 in western Kenya. FYM and tithonia were applied to supply 20 kg P ha−1 in treatments where they were used either alone or in combination with the inorganic P sources while 40 kg P ha−1 was from the inorganic P sources in the combination. Where urea was used, the inorganic P sources were applied at 60 kg P ha−1. When applied in combination with urea, MPR was a better P source for maize than TSP or BPR. However, when applied in combination with FYM or tithonia, TSP was the best P source. Treatments including tithonia were more effective in increasing maize yields than those without it with a similar total P application rate. The agronomic effectiveness of tithonia did not, however, translate to economic attractiveness, mainly due to very high labour costs associated with its use. FYM when applied alone at 20 kg P ha−1 was the only treatment that exceeded a benefit:cost ratio of 2 and, therefore, the most likely, of the tested technologies to be adopted by farmers.