Inorganic soil nitrogen distribution in relation to soil properties in smallholder maize fields in the Kenya highlands

We investigated the influence of soil charge properties on the distribution of inorganic soil N in maize (Zea mays) fields on smallholder farms in the subhumid highlands of Kenya. There was little or no fertilizer use in these subsistence farming systems. Soil NO3− was measured to 2 m depth in maize fields on 96 farms, sampled in transects at three physiographic positions (ridgetop, midslope and lower slope) in each of six soil map units (4 or 8 transects per soil map unit) covering four parent materials: acid igneous, various igneous, basic igneous, and sedimentary. Soil NO3− concentrations varied from 70 kg N ha−1. It may be difficult to accurately predict the spatial distribution of subsoil nitrate accumulation in maize from routinely measured soil variables, but our results indicate that information on parent material and subsoil CEC and clay content may help to provide broad generalizations.