ARS | Publication request: Use of a new GIS Nitrogen Index Assessment Tool for Evaluation of Nitrate Leaching Across a Mediterranean Region

Submitted to: Agriculture Ecosystems and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 11, 2008
Publication Date: March 1, 2009
Citation: De Paz, J., Delgado, J.A., Ramos, C., Shaffer, M., Barbaarick, K. 2009. Use of a new GIS Nitrogen Index Assessment Tool for Evaluation of Nitrate Leaching Across a Mediterranean Region. Agriculture Ecosystems and the Environment. 365:183-194.

Interpretive Summary: Our new GIS NIT-1 integrating GIS capabilities facilitates the identification of high-risk NO3-N leaching in a cost-effective way, and specific N management practices can be recommend per area to improve water quality. After calibration, the new GIS NIT-1 approach simulated water drainage, N crop uptake, and NO3-N leaching accurately. We can use this tool to evaluate NO3-N leaching for different N management scenarios, such as traditional management practices, BMPs, or N budgets (traditional farming management practices (conventional), BMPs, and Nmin systems) on a regional scale. Our goal was to quantitatively calibrate and validate the new GIS NIT-1 approach to quickly assess the effects of N management practices to distinguish between conditions with potential for moderate NO3-N leaching impact (>50 kg NO3-N ha-1y-1) to those with potential for high NO3-N leaching impact (>100 kg NO3-N ha-1y-1). This GIS NIT-1 shows that we can distinguish between the effects of management practices from the moderate and higher NO3-N leaching impact areas. This study is in agreement with those described by Delgado et al. (2006, 2008). It suggests that the new GIS NIT-1 approach is applicable to this Mediterranean region to distinguish between the NO3-N leaching impacts resulting from management practices used in very low and low leaching risk areas and those resulting from management practices used in medium, high, and very high NO3-N leaching risk areas.

Technical Abstract: The Mediterranean region of Valencia and its Nitrogen Vulnerable Zone have reportedly been affected by Nitrogen (N) losses from agricultural systems. Reported underground water NO3-N concentrations in this area have been as high as 99 mg NO3-N L-1. We tested the approach used by Delgado et al. (2006, 2008) which uses an annual N index tier one tool (NIT-1) to assess N losses to the environment. We developed, calibrated, and validated a new GIS NIT-1 using local and regional data sets with an Arc/Info GIS framework that programmed the algorithms using ARC macro language. This paper is the first test of the Delgado et al. (2006, 2008) NIT-1 approach under Mediterranean conditions; the first NIT-1 evaluation for citrus, artichoke, onion, and cauliflower crops; and the first correlation to outputs from the NIT-1 with underground water NO3-N concentrations. The GIS NIT-1 assessment calibration/validation and evaluation showed that implementations of Generalitat Valenciana Best Management practices can reduce NO3-N leaching by 32%, and if N budget management plans are implemented, the total NO3-N leaching is reduced by 68%. The GIS-NIT-1 approach is a potential tool for assessing N losses to the environment across the Mediterranean region.