Organic Inputs and Mineral Fertilizer Effects on Soil Chemical Properties and Maize Productivity in Central Highlands of Kenya.

Abstract

Farmers in central highlands of Kenya experience declining agricultural productivity majorly due to soil desiccation and soil fertility depletion. One way of reversing the trend of declining land productivity in smallholder farms is combined application of organic and mineral sources of nutrients. To assess the effect of combined application of organic and mineral fertilizers on soil nutrients and maize (Zea mays) a long term experiment was set in Machang’a, a drier part of the central highlands of Kenya. The trial followed a randomised complete block design with three replications. The treatments consisted of four organic sources (Tithonia diversifolia, Lantana camara, Mucuna pruriens, and goat manure) combined with mineral nitrogen fertilizer, sole fertilizer and a control. Sole goat manure, Lantana camara + 30 kg N ha^-1, and sole Tithonia diversifolia recorded the highest maize grain yield. Generally the maize grain yields were lower with the sole fertilizer treatments compared to the organics across the seasons and this could be attributed to poorly distributed rainfall. Goat manure was superior in terms of improving soil chemical properties and enhancing nutrient supply. Soil pH declined in most of the treatments, more so with the combinations of organics and mineral fertilizers compared to the sole application of organics such as Lantana camara, Mucuna pruriens and manure. Calcium in the soil increased significantly in sole Lantana camara, sole manure and Tithonia diversifolia + 30 kg N ha^-1 treatments (t-test, p = 0.029, p = 0.022, and p =0.0264, respectively). Goat manure needs to be promoted among farmers in the drier areas because of its good performance in improving soil properties.