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 waterc ourses in Finland. The emphasis of water protection policy is today on cont rolling the non-point nutrient losses from agriculture. In this study a mat hematical simulation model was used as a management tool to estimate the ch anges in nitrate (NO3--N) leaching resulting from changes in cultivation pr actices in Finnish agriculture caused by the Agri-Environmental Support Sch eme as a part of the Common Agricultural Policy of the European Union. Deta iled data were collected from about 400 farms by interviewing farmers in fo ur study areas in different parts of the country. The potential impacts of these changes on nitrate losses were then assessed by a deterministic nitro gen leaching model and regional assessments were made by combining the resu lts of model calculations with digital spatial data about soils, crops and fertilisation, using GIS-software. In general, the use of nitrogen fertilis ers (inorganic fertilisers and manure) has decreased to meet the requiremen ts of the Support Scheme. However, the estimated potential impacts on nitra te losses were rather small (3-14% in different study areas). The model res ults showed that to achieve the targeted national and international reducti ons in agricultural nitrate leaching, fertilisation and particularly manure spreading should be reduced and adjusted better to the actual nitrogen req uirements of crops. (C) 2000 Elsevier Science B.V. All rights reserved.