Nitrogen and phosphorus management on Dutch dairy farms: legislation and strategies employed to meet the regulations

Abstract

 The high input of nutrients through the use of fertilizers, manure and animal feed make it possible to reach high levels of agricultural production. However, high nutrient inputs may also result in large nutrient losses and thus have adverse effects on groundwater, surface water, and the atmosphere. To minimize nutrient emissions from agriculture, the Dutch government has introduced regulations on nutrient use. These include: (1) a ban on spreading animal manure on agricultural land during the winter, (2) the obligation to cover storage facilities for animal manure, (3) compulsory low-emission applications of animal manure to land, and (4) applying levies when the maximum permissible annual N and P surpluses for farms are exceeded. The nutrient surplus is the difference between nutrient input into the farm and nutrient output from the farm. The maximum permissible N surpluses for 2000 are 250 kg N ha^–1 year^–1 and 125 kg N ha^–1 year^–1 for grassland and arable land, respectively, and for P, 35 kg P₂O₅ ha^–1 year^–1 for both grassland and arable land. When the annual permissible levels are exceeded, farmers are charged with a levy. Results obtained at the experimental dairy farm "De Marke" showed that a reduction in nutrient inputs via fertilizers and purchased food, in combination with restricted grazing, reduced the N surplus in such a way that the NO₃ ^– concentration in the groundwater decreased to about the maximum permissible level of 50 mg NO₃ ^– l^–1. Since these results were obtained on a sandy soil that is very sensitive to NO₃ ^– leaching, it is suggested that all dairy farmers should be able to sufficiently reduce NO₃ ^– leaching by improving their farm management.