Effects of organic and mineral sources of nutrients on maize yields in three districts of central Kenya

Abstract

Trials were set up in three districts of central Kenya to evaluate organic and mineral sources of nutrients and their effects on maize yields. The experiments were set up during the long rains 2004 with fifteen different soil fertility management treatments. The treatments included cattle manure, green manures, maize stover, Tithonia, and mineral fertilizer. The test crop was maize (Zea mays), intercropped with beans (Phaseolus vulgaris). The experimental design was a Randomized Complete Block with three replicates. At final harvest at maturity, grain yield data were recorded. In general the yields were low (⩽1t ha-1) in the unfertilized control, in plots intercropped with green manure cover crops, and where maize stover alone was applied. In Kirinyaga, and Maragwa, the highest maize grain yields (6.5t ha-1) were obtained when manure was combined with mineral fertilizer. The responses were not as clear in the Kiambu site, possibly due to soil acidity at the site. There were no significant difference (p = 0.05) in grain yields between the green manure cover crops (0.4–1.5t ha-1), maize stover (0.3–0.9t ha-1) and the unfertilized control (0.4–1t ha-1) across treatments and sites during this first season. The work confirms the efficiency of combining mineral sources of nutrients with organic inputs.