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 mechanism s - urea (soluble), Floranid-32 (low water solubility) and Multicote 4 (coated fertilizer) - on maize grain and biomass yields, as well as o n plant N use. The fertilizers were applied as a top-dressing of 294 k g 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 influ ence 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 cultiva tion period was calculated from the N balance of the topsoil. Results obtained under these experimental conditions showed that the type of f ertilizer did not alter maize grain and biomass yields. Yields for mai ze irrigated with the higher NO; water were systematically greater tha n those obtained with irrigation water of low NO3- content. Nitrogen l ost from the topsoil during the cultivation period varied between 240 and 280 kg N ha(-1) for all treatments, and was well correlated with N O3--N leached into the aquifer during the same period.