This study set out to (1) calibrate and evaluate the performance of APSIM in simulating maize response to N, P and residue management and (2) identify strategies to reduce instability in crop production, and increase the efficiency of mineral fertilizer use. The response of maize to inorganic nitrogen (N) and phosphorus (P) additions were determined in the coastal savannah agro-ecology in the main rainy and secondary rainy seasons, of 2008 and 2009. Field experiments were set-up in a randomized complete block design with different levels of N (0-120 kg N ha(-1)) and P (0-30 kg P2O5 ha(-1)) mineral fertilizer. The APSIM model adequately simulated agroecosystem dynamics, resulting in the following RMSE values: anthesis (1.2 days), maturity (2.0 days), maximum LAI (0.18 m(2)m(-2)) total-biomass (543 kg ha(-1)), grain yield (318 kg ha(-1)), N uptake (12.6 kg ha(-1)), P uptake (2.2 kg ha(-1)) and in-season soil water content (0.01 mm). A long-term simulation study (30 years) showed that probabilities of obtaining higher yields were higher in the main growing season than in the secondary growing season. The efficiency of mineral N fertilizer use was also higher in the main growing season. The use of 40 kg N ha(-1) mineral N fertilizer in both seasons was more efficient than using 80 kg N ha(-1). The variability in the efficiency of mineral fertilizer use was higher in the secondary growing (44-96 %) than in the main growing season (27-48 %). Retaining crop residues yielded higher stability in grain production and increased the minimum grain yield production significantly. Applying 40 kg N ha(-1) and 30 kg P2O5 ha(-1) mineral fertilizer with crop residue retention will reduce the uncertainty in maize production, particularly in the secondary growing seasons which are characterized by prolonged drought spells. This study suggests that resource-poor farmers will be better off prioritizing the main growing season for rainfed maize production and applying a moderate amount (40 kg N ha(-1)) of N fertilizer rather than the 90 kg N ha(-1) currently recommended for the coastal savannah of Ghana in the secondary growing season because of the higher instability in yields associated with N fertilizer use in this season.
