EFFECT OF THE TYPE OF FERTILIZER AND SOURCE OF IRRIGATION WATER ON N USE IN A MAIZE CROP

An experiment in a maize crop evaluated the influence of several types of commercial nitrogenous fertilizers with different action mechanisms - urea (soluble), Floranid-32 (low water solubility) and Multicote 4 (coated fertilizer) - on maize grain and biomass yields, as well as on plant N use. The fertilizers were applied as a top-dressing of 294 kg N ha(-1). All treatments additionally received 64 kg N ha(-1) as 8.0 (N):6.5 (P):12.5 (K) compound prior to seedbed preparation. The influence of NO3- content in the irrigation water was also assessed, using water with either 2.5 or 35 mg l(-1) of NO3-. Irrigation plus rainfall totalled 513 mm (1.20 potential ET). Nitrogen lost during the cultivation period was calculated from the N balance of the topsoil. Results obtained under these experimental conditions showed that the type of fertilizer did not alter maize grain and biomass yields. Yields for maize irrigated with the higher NO; water were systematically greater than those obtained with irrigation water of low NO3- content. Nitrogen lost from the topsoil during the cultivation period varied between 240 and 280 kg N ha(-1) for all treatments, and was well correlated with NO3--N leached into the aquifer during the same period.