07 July 2012, PDF |
135 pages |
de Goffau A, Doornewaard GJ, Fraters B
RIVM Report 680717010
In 2006, the quality of shallow groundwater (the recent precipitation surplus) on farms showed a slight improvement compared to the previous year. For the regions with sandy/loess soils, the number of farms with an average nitrate concentration below the European target value of 50 mg/l has grown with nearly 10%. For the clay and the peat regions the number of exceedances has remained nearly constant. This is the outcome of data from the Minerals Policy Monitoring Programme (LMM). The LMM has been established to assess and explain the evolution of water quality on farms in relation to sector policies and agricultural practice. Water quality is linked to the agricultural practice in the preceding year. LEI and RIVM administer the programme. Since the nineties of last century, the use of nitrogen in fertilizers as well as the nitrogen soil surpluses at dairy farms has gone down. After 2000 this falling trend flattened out. This declining trend is less clear on arable farms. In 2005, the total nitrogen application for different combinations of farm types and soil types varied between average values of 198 and 424 kg/ha; the corresponding values for phosphorous fertilizer ranged from 85 to 125 kg/ha. The input of nitrogen and phosphate into the soil continues to exceed nutrient removal in harvested crops. The nitrogen surplus on the soil balance varied from 105 to 188 kg/ha and the phosphorous surplus from 23 to 44 kg/ha. The average nitrate concentration measured in the shallow groundwater on farms also decreases since the 1990s. Nevertheless, on 51% of the farms sampled in 2006, the nitrate concentration was found to be above the European target value. Most of the exceedances were encountered at farms in areas with sandy/loess soils (59%). Significantly fewer exceedances were observed at farms in areas with clay soils and peat soils (39 and 0%, respectively).