Effect of selected organic materials and inorganic fertilizer on the soil fertility of a Humic Nitisol in the central highlands of Kenya

The effect on soil fertility of applying particular organic resources to a humic Nitisol in the central highlands of Kenya was studied. The organic resources ( Calliandra calothyrsus , Leucaena trichandra , Tithonia diversifolia , Mucuna pruriens , Crotalaria ochroleuca and cattle manure) were either applied solely or along with inorganic fertilizer in a cropping trial using maize as the experimental crop. After 4 years of continuous cultivation and manuring, soil fertility effects varied among treatments. Cattle manure proved to be the most effective and improved soil fertility by increasing pH, cations (Ca, K and Mg), and C. Calliandra, Leucaena, Tithonia and herbaceous legumes generally reduced soil pH, C and N but increased Ca, K and Mg. Cattle manure is therefore an important resource for maintaining soil organic matter (SOM) in the area and in other similar areas with arable‐livestock systems. Reduction of soil C and N by the high quality organic materials suggests that their role in maintaining SOM in the long‐term is limited in this area. A sound nutrient management system should strive to make a balance between maximizing crop production and sustaining soil quality.