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Agricultural practices and water quality on farms registered for derogation in 2014

Landbouwpraktijk en waterkwaliteit op landbouwbedrijven aangemeld voor derogatie in 2014

Synopsis

Dutch agriculture is highly productive and efficient. The use of minerals is necessary for efficient production of crops, but also has undesirable (environmental) effects. The Dutch minerals policy seeks to minimise adverse environmental impacts, whereby monitoring is an essential component. This consists with international agreements on the use of minerals and monitoring the impact of policies.

Conform the EU Nitrates Directive, the member states are required to limit the use of livestock manure to a maximum of 170 kg of nitrogen per hectare per year. Dutch farms growing grass on at least 80 per cent of their total agricultural area were in 2014 allowed to deviate from this requirement under certain conditions. This exemption from the standard of 170 kg nitrogen is referred to as 'derogation'. LEI Wageningen UR and RIVM monitor agricultural practices and water quality at 300 farms, which have been granted derogation and annually report the results to the EU. This study shows the results in 2014 and trends between 2006 and 2015. The report concludes that the average nitrate concentration in groundwater on these farms has stabilized or decreased in this period.

Agricultural practice
This report shows that, on average, derogation farms in 2014 applied 237 kg of nitrogen per hectare in the form of livestock manure. The quantity of nitrogen that can potentially leach into groundwater in the form of nitrate is partly determined by the nitrogen soil surplus. This surplus is defined as the difference between nitrogen input (e.g. in the form of fertilisers) and output (e.g. via harvested grass and maize). The average nitrogen soil surplus in the Netherlands has not changed substantially during the period studied, but in 2014 it decreased considerably due to the good growing season for grass and maize.

Groundwater quality
In 2014, the average nitrate concentration in groundwater on derogation farms in the Sand Region amounted to 40 milligrammes per litre (mg/l), and was therefore below the nitrate standard of 50 mg/l. On average, farms in the Clay Region and Peat Region had lower nitrate concentrations (15 and 9.5 mg/l, respectively). Derogation farms in the Loess Region had an average nitrate concentration in groundwater of 51 mg/l. The differences between the regions are mainly caused by a higher percentage of soils prone to nitrogen leaching in the Sand Region and Loess Region. Less denitrification (microbial decomposition of nitrate) occurs on these soils, and more nitrate can therefore leach into the groundwater.
 

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