Soybean contribution to nutrient balance in a cassava (manihot esculenta crantz) based cropping system.

The effects of varying levels of applied fertilizer and nutrient contribution of soybean on soil nutrient nitrogen and potassium (N and K) balance in a cassava/soybean intercrop system was studied at Nsukka in a derived Savannah location of South Eastern Nigeria. Two varieties of cassava and six varieties of soybean of three maturity groups were grown as sole and intercrop with four rates of N and K fertilizer. Four input and four output processes were used to quantify the partial nutrient balance of the system. The results showed that sole cassava had negative N and K balances at N0K0 and N45K0 fertilizer rates and positive balance at only N45K50 fertilizer rate. Application of N0K50 fertilizer rate gave the highest positive N and K balances. Intercropping cassava (NR 8230) with medium maturing variety of soybean, (TGX 1894-3E) gave the highest N and K balances (+44.06 Kg N ha-1 and +72.70Kg K ha-1 respectively). Soil-N and Soil-K reserve were highest at TGX 1894-3E by N0K50, Addition of soybean residue into the intercropping system improved soil nutrient status and resulted in positive nutrient balance. Cropping cassava without soybean residue management and starter nitrogen (N0K0) led to negative nutrient balance (-27 Kg N ha-1).