The effect of nitrogen (N) fertiliser on maize grain yield was measured at 42 sites over three seasons.In 20 trials there was no significant increase in grain yield (P0.05).A single predictive relationship was derived for the N response of maize grain crops across a wide range of climates, crop managements, and soil types.It is therefore possible to predict the increase in grain yield following N fertiliser application, by using the expected yield when a given amount of N is applied in starter fertiliser and the potential yield of each crop.The former parameter can be derived from a relationship established between mineral N determined in soils (0-600 mm) collected in early October (dried at 33#xB0;C) and maize grain yield, and the latter from district and farm records.A N response curve can then be estimated for a particular crop.This will considerably improve the precision in optimising N fertiliser applications.
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