Effect of Lime, N and P Salts on Nitrogen Mineralization, Nitrification Process and Priming Effect in Three Soil Types, Andosols, Luvisols and Ferralsols

Abstract: Incubation studies were conducted to determine the effect of lime at the rate of 10tons ha-1, Diammonium phosphate and Ammonium sulphate at 200kgha-1and Triple Superphosphate at 100kg ha-1 on nitrogen mineralization, nitrification process and priming effect. Three soil types were used namely luvisols from semi-arid Katumani, andosol and ferralsols from sub-humid Gituamba and Kitale, respectively. The soils were selected on types, pH, soil organic carbon content, land use and Climate. The soils were incubated aerobically in polythene bags for 120 days at room temperature and mineral N determined at specified periods during the experiment. Mineralized N was significantly higher (p≤0.05) under the various treatments compared to the control except for Kitale ferralsols. In the ferralsols, liming though it increased N mineralization was not significant compared to the control. Addition of salts increased production of mineral N suggesting a priming effect where DAP, AS and TSP were added. Addition of TSP and DAP increased N mineralization and was attributed to steady increase in microbial biomass as a result of P. The N mineralization rates were higher in the topsoil compared to the subsoil with the Andosols registering highest amounts released. Nitrate production was positively correlated with soil pH in Gituamba andosols only and this could be attributed to presence of acid adopted strains which are active at low pH levels.