Estimating the effect of legislation on nitrogen leaching by upscaling field simulations

The aim of this article is to present an approach for estimating nitrogen (N) leaching on a regional scale, e.g. municipality and country. This approach is used in scenario studies of the effects of implementation of legislation on the N fertilization schedules on N leaching. On the basis of simulated results obtained with the deterministic simulation model DAISY by Hansen et al. (Fert. Res. 27 (1991) 245–259.), for different combination of farm types, N-fertilization schedules, soil types, irrigation and climate, a statistical model called General Nitrogen Leaching model (GNL-model) is set up. The model describes the average annual N leaching as a linear function of the number of livestock units per hectare for the selected class variables. The GNL-model is used in a regional model to simulate N leaching at municipality level, in the mid-eighties and after full implementation of the legislation. As input to the regional model are statistical farm data (farm type, number of animals, cultivated area, and irrigated area) in 1985 and 1994 and soil data. Soil data is represented by soil types as distributed at municipality level. The results simulated at municipality level are summarized to give the national level. N leaching was found to be ca. 200 000 t N ha−1 year−1 in the mid-eighties and ca. 130 000 t N ha−1 year−1 after full implementation of the legislation. It was found that the approach worked well in estimating the effect of the changes in N fertilization schedules caused by implementation of the legislation.