1 International Plant Nutrition Institute, Box 30772, Nairobi, Kenya, 00100, www.ipni.net, email@example.com
Poor soil fertility is a major constraint to crop productivity on smallholder farms in sub-Saharan Africa. This study evaluated the effects of soil type, soil fertility status and nutrient source on maize productivity and partial factor productivity (PFPN) of fertilizer N in north-east Zimbabwe. Four on-farm sites representative of major soil fertility categories in the region were selected for the study: (i) depleted sandy soil (DSS); (ii) sandy soil (SS); (iii) depleted clay soil (DCS); and clay soil (CS). Fertilizer and manure treatments were applied over nine cropping seasons as follows: (i) no fertilizer; (ii) 100 kg N/ha; (iii) 100 kg N/ha + cattle manure (15 t/ha); (iv) 100 kg N/ha + 30 kg P/ha in combination with 20 kg Ca/ha, 5 kg Zn/ha and 10 kg Mn/ha. Initial maize yields were in the order DSS<DCS<SS<CS. Across all trials, maize grain yield response and PFPN values in the sole N-fertilizer (100 kgN/ha) treatment were low, indicating multiple constraints to crop productivity. Yields on the sandy soils were marginally increased with balanced fertilizer application. Across all fields, the highest yields and PFPN after nine seasons were achieved with application on N in combination with manure, indicating the importance of manure in maintaining soil fertility, maize productivity and optimum PFPN levels in smallholder farming systems where crop residues are removed to use as livestock feed.