Abstract

The RIVM and the LEI have pooled data on farm practices and groundwater quality obtained from agricultural enterprises sampled in 2003 within the framework of the Minerals Policy Monitoring Programme (LMM). The data on farm practices of dairy farms reveal a marked reduction in fertilization application and nutrient surpluses since the late 1990s as well as an apparent stabilization since 2000. This trend is much less evident in the data set on arable farms.
The nitrate concentration in the upper groundwater (recent rainfall surplus) of 42% of the farms sampled is higher than the European target value of 50 mg/l. Most of these exceedances were found on farms situated on sandy/loess soils (53%), while significantly fewer exceedances were observed for farms situated on clay soils (12%). The nitrate concentration has decreased since the 1990s on farms located in both soil regions. All measurements on farms located in peat regions were below the EU target value. A lower concentration of nitrate in the upper groundwater on farms places less strain on the environment.
The LMM has been established to assess and account for the quality of groundwater on farms in relation to environmental pollution, governmental policies and farm practices. The quality of the groundwater is determined by measuring the levels of nutrients (including nitrate) in the upper groundwater (just below the root zone). Measurements in this part of the soil profile reveal the proportion of the nutrient surplus that has been transferred into the groundwater. The measurements were carried out on representatives of the most common types of farms in the Netherlands (arable and dairy farms) in the three main soil regions (sand/loess, clay and peat).