Concentration of nitrate in upper groundwater

Over the last few years, the amount of nitrate in the upper groundwater layer of agricultural sandy soils has declined to the extent that the target value of 50 mg per litre has been achieved. In regions with clay and peat soil in particular , concentrations have been below the target for some time, mainly due to stricter fertiliser standards. Groundwater concentrations under agricultural loess soils are just above the target value.

The issue

Green growth requires a healthy balance between economy and natural resources. Groundwater is used in the Netherlands to prepare drinking water. Leaching of nitrogen from farmland to the groundwater threatens its quality. High concentrations of nitrate can lead to closure of drinking water abstraction points or to higher purification costs. A key determinant of nitrate concentration in the groundwater is the nitrogen surplus in the soil balance of farms. In order to reduce the load of nitrogen to soil and groundwater, the standards for nitrogen fertilisation on agricultural land have been tightened in stages. The effect of this on nitrate content has become visible in recent years (CBS, PBL, RIVM, WUR, 2016 and LMM, 2018).

Analysis

There is a large spread in nitrate concentrations between agricultural sectors, farm types and regions with regard to soil type. Soils under arable farms generally have a higher nitrate surplus than soils under dairy farms. In the southern part of the Netherlands, with sandy soils, concentrations are generally higher, among other things because crops are cultivated on soil types that are susceptible to leaching.