Use of a new GIS nitrogen index assessment tool for evaluation of nitrate leaching across a Mediterranean region Jose M. De Paz a,1 , Jorge A. Delgado b, * , Carlos Ramos a,2 , Marvin J. Shaffer c , Kenneth K. Barbarick d a Centro para el Desarrollo de la Agricultura Sostenible, Instituto Valenciano de Investigaciones Agrarias, Carretera Moncada-Náquera km 4,5. Apdo, Oficial 46113 Moncada, Valencia, Spain b USDA-ARS, Soil and Plant Nutrient Research Unit, 2150 Centre Avenue, Building D, Suite 100, Fort Collins, CO 80526, USA c USDA-ARS (retired), Loveland, CO 80538, USA d Soils and Crops Department, Colorado State University, Fort Collins, CO 80523, USA article info Article history: Received 22 March 2008 Received in revised form 31 August 2008 Accepted 11 November 2008 Keywords: Ammonia volatilization Denitrification Nitrate leaching GIS NUE Nitrogen index summary Traditional nitrogen (N) management practices with excessive N fertilizer application and higher N losses to the environment are more widely used than the recommended best management practices (BMPs) across the nitrogen vulnerable zone (NVZ) of the Mediterranean region of Valencia. Since reported under- ground concentrations for this region are as high as 100 mg NO 3 –N L 1 , nutrient managers and policy makers need quick tools that qualitatively rank N management and their respective N losses to the envi- ronment in order to implement BMPs across the region. Our hypothesis was that a new tier one GIS N index tool (GIS NIT-1), based on quantitative N mass balance and qualitative rankings, can be used to assess N management practices across the NVZ. The new GIS NIT-1 assessment tool was able to simulate N uptake, hydrology characteristics (water leaching), N dynamics and NO 3 –N leaching across several sites of the NVZ (P < 0.001). This study suggests that the GIS NIT-1 can be used to quickly identify practices that produce very low to moderate N losses to the environment from those with high and very high N rankings. Published by Elsevier B.V. Introduction Nitrogen (N) inputs are necessary to maintain viable econom- ical agricultural production across worldwide agroecosystems. Although N inputs are necessary to maintain viable agroecosys- tems, higher than needed N inputs are reported to increase losses of N through the nitrogen cycle, impacting groundwater, air, and soil quality (Antweiler et al., 1995; Gruber and Galloway, 2008; Juergens-Gschwind, 1989; Kronvang et al., 2001; Wriedt et al., 2007). One of the key principles for minimizing nitrate–nitrogen (NO 3 –N) leaching is to manage N applications with a mass bal- ance approach (Meisinger and Delgado, 2002), however the quan- tification and assessment of N lost via surface, leaching, and atmospheric pathways is difficult (Delgado, 2002). Computer models provide a quick way to evaluate the effect of best manage- ment practices (BMPs) across regions, integrating layers of infor- mation and site-specific variability to determine what can be done to protect water resources (Almasri and Kaluarachchi, 2004, 2007; Delgado, 2001; Jordan and Smith, 2005; Morari et al., 2004; Peralta and Stockle, 2001; de Paz and Ramos, 2002, 2004). There is a demand for the development, calibration, and valida- tion of fast-working tools that can assess N losses to the environ- ment, specifically NO 3 –N leaching loss impacts on groundwater in Europe. The European Commission established a series of guidelines and directives to protect water from pollution created by NO 3 –N linked to agricultural sources (CEC, 1991). In Spain, each regional government has to follow this EU directive. The Valencia region (Generalitat Valenciana, 2000a) declared most of the irrigated Med- iterranean region of Valencia a nitrogen vulnerable zone (NVZ) and recommended the application of a new set of BMPs to preserve water quality. However, traditional farm practices are still more widely used than the recommended BMPs across the NVZ. The NO 3 –N con- centrations in groundwater are still high in several Valencian aqui- fers (Rubio et al., 2006). Traditional farming practices apply high N fertilizer rates to the large vegetable and citrus areas across this Mediterranean region of Spain. There is currently a need for scien- tists to develop, calibrate, and validate a quick GIS NIT-1 tool for quick assessment of N management practices across this region. Applying complex models across large areas with scarce data may not be the best approach because of the large uncertainty introduced (Beven, 1989). Simpler models may offer faster 0022-1694/$ - see front matter Published by Elsevier B.V. doi:10.1016/j.jhydrol.2008.11.022 * Corresponding author. Fax: +1 970 490 8213. E-mail addresses: jmpaz@ivia.es (Jose M. De Paz), Jorge.delgado@ars.usda.gov (J.A. Delgado). 1 Dr. De Paz was a Visiting Scientist at the USDA-ARS, Soil Plant Nutrient Research Unit and Faculty Affiliate with Colorado State University, Fort Collins, CO, USA. 2 Tel.: +34 963424000; fax: +34 963424001. Journal of Hydrology 365 (2009) 183–194 Contents lists available at ScienceDirect Journal of Hydrology journal homepage: www.elsevier.com/locate/jhydrol