How to manage nitrogen fertilisation for vegetable crops in accordance with government regulations in the Netherlands

Government regulations in the Netherlands for restricting nitrogen used in vegetable production are based on nitrogen surplus which is estimated using a mineral declaration system (MINAS). The permissible nitrogen surplus is calculated as the difference between the input and output of nitrogen for t he whole cultivated area of the farmer concerned. The N surplus will be set at 150 kg N ha(-1) for the year 2000 and decreased to 100 kg N ha(-1) by t he year 2008. In 1990 PAV began six years of research on Integrated Vegetab le Farming Systems on four experimental farms situated in the main growing areas in the Netherlands. Two sites were situated on sandy soils and two on marine clay soils. At every location there were three or four crop rotatio n plans including systems that were intensive, common to the region and oth ers that were extensive and contained grasses and cereals in addition to ve getable crops. All crops of the four systems at the four locations were har vested and separated into marketable yield and residues and analysed for th eir N content. The N content of the soil was determined in the 0-30, 30-60 and 60-90cm layers at selected growth stages. With this data the MINAS norm could be calculated for the six years of experimentation. The MINAS norm d id not show any surpluses greater than 85kg N ha(-1). This was low enough t o meet the MINAS norm for 2008. But on one site (Westmaas) the MINAS norm f or the 1:3 crop rotation will be exceeded in 2002.