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Leaching of nitrogen surplus to groundwater and surface waters on farms : Recalculation of leaching fractions

De uitspoeling van het stikstofoverschot naar grond- en oppervlaktewater op landbouwbedrijven : Herberekening van uitspoelfracties

Synopsis

In this study, the degree of leaching of the nitrogen surplus to groundwater and surface waters is calculated per soil type for arable land and grassland for the 1991-2009 period. The nitrogen surplus is the difference in the amount of nitrogen, for example, from inputs via artificial fertilisers and manure and removals of nitrogen from the harvest of crops. This amount of nitrogen that remains in the soil can leach to groundwater and surface waters. Leaching differs between soil types and methods of land use. The results of this study differ only slightly from the results of a previous study where data for the 1991-2004 period were used. These data will be used to derive standards (with the use of a model) for environmentally safe use of total nitrogen and animal manure nitrogen. Leaching differs between soil types Of the three soil types considered, nitrogen leaching levels were highest in sandy soils, followed by clay soils and lowest in peat soils. For arable land on well-drained sandy soils, about 90% of the nitrogen surplus leaches from the root zone. This percentage is lower, however, for poorly drained sandy soils with shallow groundwater. This is due to the more favourable soil conditions for the degradation of nitrate nitrogen so that nitrate does not leach to the ground and surface waters. For grassland on peat soils, only 5% of the nitrogen surplus leaches. Here, almost all nitrate nitrogen is degraded. New nitrogen use standards in 2014 These data are important in the prevention of too much leaching of nitrogen to groundwater and surface waters due to fertilisation. The European Nitrates Directive obliges all Member States to prevent this from occurring. The Netherlands have developed a system of nitrogen use standards that limits both total nitrogen use and nitrogen use via animal manure. These standards are evaluated every four years; they will be determined again for the 2014-2017 period. For this study, data were used from the Mineral Policy Monitoring Programme (LMM) of RIVM and LEI, part of Wageningen University and Research Centre.
 

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