Estimation of the impact of fertilisation rate on nitrate leaching in Finland using a mathematical simulation model

Agriculture comprises the largest single source of nitrogen (N) into watercourses in Finland. The emphasis of water protection policy is today on controlling the non-point nutrient losses from agriculture. In this study a mathematical simulation model was used as a management tool to estimate the changes in nitrate (NO3--N) leaching resulting from changes in cultivation practices in Finnish agriculture caused by the Agri-Environmental Support Scheme as a part of the Common Agricultural Policy of the European Union. Detailed data were collected from about 400 farms by interviewing farmers in four study areas in different parts of the country. The potential impacts of these changes on nitrate losses were then assessed by a deterministic nitrogen leaching model and regional assessments were made by combining the results of model calculations with digital spatial data about soils, crops and fertilisation, using GIS-software. In general, the use of nitrogen fertilisers (inorganic fertilisers and manure) has decreased to meet the requirements of the Support Scheme. However, the estimated potential impacts on nitrate losses were rather small (3-14% in different study areas). The model results showed that to achieve the targeted national and international reductions in agricultural nitrate leaching, fertilisation and particularly manure spreading should be reduced and adjusted better to the actual nitrogen requirements of crops. (C) 2000 Elsevier Science B.V. All rights reserved.