The integrated modeling system STONE for calculating nutrient emissions from agriculture in the Netherlands

For the Netherlands, a nutrient emission modeling system, called STONE, has been developed. It was designed for evaluation at the national and regional scale of the effects of changes in the agricultural sector (e.g. changes in fertilizer recommendations and cropping patterns) and in policy measures (e.g. EU nitrate directive for ground water) for the leaching of nitrogen (N) and phosphorus (P) from agricultural land areas to ground water and surface waters. STONE consists of a chain of models, which are applied subsequently to a large number (6405) of unique units that represent the variation in biophysical conditions in the Netherlands. This paper discusses the main components of the STONE model chain, covering manure excretion and distribution, NH3 emission and deposition, N and P uptake by crops, transport and immobilization of N and P in soils, and leaching of N and P to surface and ground water. The plausibility of the results from STONE is studied by analyzing the approach and calibration of the different models within STONE and the validity of the models’ results. An overview of weak and strong components within STONE is presented. It was found that computed results on nutrient leaching to ground and surface waters from STONE compare fairly well with observations. A number of aspects that may limit the plausibility of the results generated by STONE are discussed. The models’ capability is illustrated by results from an application. In this study the effects of a number of possible policy measures on fertilizer use within Dutch agriculture are explored for the coming 30 years. The computed future nutrient emissions indicate the efficacy of various policy measures and the location of eutrophication-sensitive areas in the Netherlands.