Application of NLEAP model to evaluate the Nitrogen fertilizer management in Argentina and Spain

LAVADO,R.S.,; DE PAZ,J.M; DELGADO, J; RIMSKI-KORSAKOV,H

Advances in nitrogen management for water quality

SWCS

Lugar: Ankeny IA EE.UU; Año: 2010; p. 314 - 343

  Present Chapter deals with the nitrogen status and the advances in the use of NLEAP model in two countries, located in different continents (South America and Western Europe. Soybean is the most important crop of Argentina and this crop do not receive nitrogen fertilization. When soybean is excluded from calculations, the annual Argentinean nitrogen doses almost doubled, reaching 44 kg N ha-1 instead 26 kg N ha-1 estimated the last year. Anyway, it means around a third of the Spanish consumption of nitrogen. Even taking account this differences of nitrogen fertilization, the problem of the nitrate leaching is present in both countries, as it is summarized below. The nitrogen management and problems in both countries show somewhat similar picture but divided by different factors: fertilizers applied in excess to crop requirement appears to be the main cause of present groundwater enrichment with nitrates. On the other hand, nitrate leaching in Argentina is a new issue and fertilizers are not entirely responsible for the problem. The mineralization of soil organic matter speeded up by the agriculture appears to be the main responsible in the near past. In both cases management of nitrogen became an imperative for a sustainable crop production. In that scenario arise the NLEAP model. This model is a versatile and allows the calculation potential losses of nitrates making use of easily obtained or estimated inputs to run in any local conditions. It needs, however, some additional adjustments to predict residual nitrates and nitrate leaching for a more reliability application of NLEAP in the Argentinean and Spanish conditions. In Spain, the screening analysis of NLEAP model linked to a GIS gives a useful tool to estimate the potential N leaching at regional scale. This tool also can be used to evaluate the NO3-N leaching from different management practices in a cost-effective way. In this study, the nitrogen doses recommended by the GAP reduced the NO3-N leaching 35% from a conventional management. A higher reduction is possible if the farmer use some other fertilizer recommendation system or a detailed simulation model to optimize the management practices. The NLEAP model (monthly analysis) allowed us a more detailed analysis of nitrogen management and uptake efficiency for several crops. After a slight calibration, the model simulated acceptably well both the water drainage and the NO3-N leaching. Although a more extended calibration and validation in other conditions would be needed, the model can be used as a tool to know the effect of the climate, crop, irrigation and nitrogen fertilization practices in the nitrate leaching, and is also valuable to support the fertilizer decision, and provide information about N leaching. The NLEAP model is starting to be used to develop management strategies to improve the nitrogen fertilization efficiency, reducing the nitrates leaching risk increasing crop yield in the less developed area, the Pampas. Future uses of the model using GIS technology would be valuable to detect areas of high risk of aquifer contamination, under some differences in soil properties, management, fertilization doses and application moments, complementary irrigation, crop rotation and so on.