Abstract
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).
Highlights
Nutrient budgets are used as indicators for the sustainability of land use system (Dechert et al, 2004)
Four fertilizer rates were randomised in the main plot, while twenty cropping systems comprising six sole soybean, two sole cassava and twelve cassava/soybean intercrop were randomised in the sub- plots
When adequate K was supplied through mineral fertilization and nitrogen made available through biological nitrogen fixation, the nutrient balance improved
Summary
Nutrient budgets (input and output balances) are used as indicators for the sustainability of land use system (Dechert et al, 2004). By using nutrient budget analysis, agricultural production systems which are not sustainable, either because of nutrient depletion, leaching or volatilization are identified. According to FAO (2003), agricultural intensification without adequate restoration of soil fertility threatens sustainability of agriculture. The challenge is to preserve land against nutrient depletion and to make it productive. Loss of soil nutrients a serious threat to sustainable crop production (Van der Pol and Traore, 1993) With the prevailing farming system in the derived Savannah zone, yields are bound to drop because of continuous nutrient mining through crop yield without adequate replenishment from crop cycle to crop cycle. Excessive use of chemical fertilizers results in high soil acidity and increased land degradation (Ladha and Reddy, 2003) Intercropping with soybean and utilizing the crop residue plays important role in improving nitrogen economy (Umeh, 2002)
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