Nitrogen and Phosphorus Fertilization Effects on Crop Residue and on Soil Carbon,Nitrogen and Phosphorus in Northern Ghana.

Sustainable management practices are needed to enhance soil productivity in degraded soils in semi-arid West Africa. Field experiments were conducted during 2003 to 2006 cropping seasons to study the effects of three nitrogen (N) and three phosphorus (P) fertilization rates on crop biomass returned to the soil, the C, N and P concentration of crop residue, and the impact on soil organic carbon (SOC), total soil nitrogen (TSN) and total soil phosphorus (TSP) in the 0-20 cm soil depth. Annual biomass production and crop residue returned to the soil was significantly increased 60 – 70% when N and P fertilizers were applied compared with no fertilization or when only N and P was applied. Residue C, N and P concentrations were greater with N or P fertilization than when fertilizer was not applied. Total soil N was not affected by N and P fertilization but TSP was increased significantly with P fertilization. Averaged across years, SOC and TSP in the 0 – 20 cm soil depth was greater with N and P fertilization compared with no fertilization or only N or P fertilization. We conclude that SOC and TSP can be enhanced by increasing crop residue production through adequate N and P fertilization and returning residues to soil over a longer period as observed in some studies.