Assessing the impact of Nitrate Vulnerable Zones in England on nitrate loss from agricultural land

Abstract

The impact of the 2002 Nitrate Vulnerable Zone Action Programme (NVZAP) in England was assessed using survey data linked to modelling. Baseline nitrate losses were estimated using the NEAP‐N national model, and impacts of individual measures were estimated by linking survey data on land management change to models or impact estimates derived from controlled experiments. Results were scaled up using mapped agricultural census data. The reduction in nitrate leaching attributable to the 2002 NVZAP was estimated as 5%, the majority being due to better adjustment of fertiliser inputs to crop requirement and manure‐derived N. Closed periods for manure application in autumn were locally effective, especially within arable systems, but the national impact was small because of the small land area affected. Overall impacts were greatest on sandy soils with large poultry or pig units, where losses were previously very high, and least on extensive grassland systems, where losses were previously low. Some mitigation measures had little impact because good practice is already widespread or because they targeted surface runoff pathways, which are more important for pollutants such as P, sediment, ammonium and pathogens. The potential evolution of measures is discussed along with some key limitations and uncertainties associated with the estimation process.