A high nitrate pollution of groundwaters has been detected in recent years in many areas of southwest Spain where maize is cropped. This may be caused by the high fertilization level used in those areas. In this work, maize was grown consecutively for six years (1991–96) under Mediterranean management practices in the Guadalquivir River Valley (southwest Spain), using both a fertilization level widely used in the area (510 kg N ha‐1yr‐1) and one third of it. The effect of the reduced fertilization on crop development, yield parameters and kernel analysis was studied. Nitrate leaching for each fertilization treatment was also monitored, during one experimental year. Crop development was slightly poorer in the plot with reduced fertilization, but no differences in yield were found. The only effect on kernel composition was a higher nitrogen (N) concentration in the kernels of the plot with the higher fertilization level. The amount of N supplied by the reduced fertilization, together with the N in the irrigation water and from the soil mineralization, was enough to counterbalance the N removed by the crop in years of high production. Nitrate leakage was three times greater in the plot with the higher fertilization level than in the plot with reduced fertilization. A marked reduction in crop performance was observed in both plots in the first three experimental years. Some stabilization was observed afterwards.