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Nitrogen induced an increase in agriculture production and contributed to the growth of the world population. However, the overuse of nitrogen resulted in the pollution of water resources. The expansion of agriculture in Argentina is a good example of the abuse of nitrogen fertilization, but little is known about the damage induced in water quality. The objectives of this study were to (i) Adjust and validate the LEACH-W model simulations with data observed in the field, (ii) quantify nitrate concentrations in the drainage water, (iii) quantify N leaching from a corn-cropped soil, (iv) calculate a simplified soil-plant N balance. Treatments consisted of 0, 100 and 200 kg N ha-1 applied at planting in a RCBD with 4 replications. Ceramic suction cups, and the LEACH-W model were used to measure and model nitrate leaching, respectively. Nitrate leaching was related to drainage events, and nitrate levels in drainage water surpassed 10 mg L-1 of NO3--N in the fertilized treatments. Nitrate leaching was enhanced by the presence of high residual soil nitrate levels. Losses from the fertilized treatments represented 27 and 17% of the applied N for the 100 and 200 kg N ha rates, respectively. Nitrogen fertilization of maize is a threat of contamination of groundwater in the SE region of Buenos Aires, despite the fact that the doses of nitrogen fertilizer are lower than those used in other parts of the world.