Simulation of nitrate leaching for different nitrogen fertilization rates in a region of Valencia (Spain) using a GIS-GLEAMS system

The groundwater loading effects of agricultural management systems (GLEAMS) model coupled to a GIS was used to evaluate the effect of different fertilization treatments on the total N leaching in a selected area of eastern Spain with intensive agriculture. Four nitrogen fertilization rates (traditional or base, base rate reduced by 20%, reduced by 50%, and the rate calculated by the N-min recommendation system for vegetables, and reduced by 70% for citrus) were evaluated at a regional scale to find the rate that minimized N leaching without reducing crop N uptake. Nitrate leaching maps were obtained for the different nitrogen rates studied. A great reduction of N leaching (up to 68% for vegetables, and 75% for citrus) was observed under the most reduced fertilization rates and this reduction was greater in areas irrigated with surface water in comparison to those irrigated with groundwater. The GIS-GLEAMS system was a useful tool to assess the N leaching at a regional scale for the different N management considered. For example, it was shown that the N-min recommendation system was the most efficient for vegetables, and for citrus the most efficient fertilization rate was the reduced 50%, that is similar to that recommended by the Code of Good Agricultural Practices. The areas irrigated with groundwater with high nitrate content had a high leaching rate, and the nitrate applied in irrigation water should be considered when planning the crop fertilization. A temporal analysis of the NO3-N in soil, N leaching, crop evapotranspiration and rainfall allowed to identify the influence of the soil NO3-N and the rainfall on nitrate leaching. (C) 2003 Elsevier B.V. All rights reserved.