Drainage and N-leaching in alluvial soils under agricultural land uses: Implications for the implementation of the EU Nitrates Directive

A combination of factors associated with the physical substrate (soil texture, infiltration rate, field capacity) and the agricultural use (under conventional or ecological production systems) determined the final nitrogen leaching load from each plot. The plots located in the middle section of the aquifer (sites 1 and 2, with shallow, stony soils) generated more intensive drainage and higher N-leaching than the plot located in the lower section (Site 3, with a deep, fine textured soil), where there was no drainage, nor N-leaching. Paradoxically, the Site 3 plot was the only one found within the NVZ designated perimeter. It was also observed that when the degree of vulnerability associated with the textural characteristics of the substrate was high, drainage and N-leaching could be affected by the agricultural production model. These results support the proposal of Arauzo et al. (2011) to designate, as a general criterion, the entire alluvial area as a NVZ.