Simulating nitrogen fertilizer response in low-input farming systems of Malawi

This paper reports on the validation of the Agricultural Production Systems Simulator (APSIM) model for simulating the response of maize to N fertilizer in low-input maize production systems in Malawi and Zimbabwe, with a special focus on the marginal benefit from using small amounts of fertilizer, rather than applying it at optimal rates. In 1998/99, in experimental plots where no N fertilizer was applied, yields varied from 442 to 4,800 kg/ha across 5 sites. The model simulated yields in the range of 1,277-4,784 kg/ha for the same locations. Actual response to 69 kg/ha of applied N varied over the 5 experimental sites chosen for the validation exercise using data for 1997/98 and 1998/99. The model accurately simulated a response to applied Nat four of the five trial sites selected for the validation test.