In 2024, the average quantity of nitrate in upper groundwater under derogation farms was well below the European standard. This was mainly because of the large amount of precipitation in 2023 and 2024, resulting in more nitrate being broken down in the soil and mixed with a greater volume of water. This has become apparent from annual measurements by RIVM at 300 grassland farms using derogation.
Because of the alternating extremely dry and extremely wet years, nitrate levels at farms have fluctuated widely in recent years. Since 2017, there has barely been any improvement in groundwater quality. In some regions, the quantity of nitrate in groundwater has been structurally too high. Efforts to improve groundwater quality therefore remain necessary at derogation farms.
What is derogation?
Since 2006, some farms in the Netherlands have been allowed to use more animal manure on their land than is permitted under the European Nitrates Directive. These are dairy farms with a lot of grassland, because grass easily breaks down nitrate. This partial exemption is known as a ‘derogation’. Every year, RIVM and Wageningen Social & Economic Research examine the same 300 derogation farms, looking at how much manure they use and how much nitrate is measured in the groundwater. The current derogationscheme will end this year.
Fluctuating results due to alternating dry and wet years
The low quantity of nitrate in the groundwater is due to above-average precipitation in 2023 and 2024. When the groundwater level is high, more nitrate is broken down in the soil and mixes with more water. This results in less nitrate in the groundwater. The period from 2018 to 2020 was dry, because there was less rainfall. Less nitrate was broken down in the soil in those years, resulting in higher quantities of nitrate in the groundwater. So far, 2025 has been a dry year. This may affect water quality.
No improvement in the long term
Between 2006 and 2017, there was a clear reduction in the average quantity of nitrogen in groundwater under derogation farms. This was the result of smarter use of manure and a higher percentage of grassland. After 2016, instead of clear improvements, the measurements showed fluctuating nitrate levels resulting from extreme weather conditions.
Impact of drought on water quality
Earlier this year, RIVM published a study on the regional effects of drought on the quality of groundwater in agricultural areas. This study showed that drought results in more nitrogen remaining in the soil in the form of nitrate. Among other reasons, this is due to groundwater levels, which drop during long droughts. If there is less water in the soil, bacteria are less able to break down nitrate and plants do not absorb as much nitrogen.
After a dry spell in summer, the built-up nitrate leaches into the surface water or groundwater in the autumn due to rain. However, if the autumn and winter likewise see insufficient rainfall, the ground remains too dry. It then takes longer for the built-up nitrate to leach into the surface water or groundwater. How fast this happens following a drought depends on the type of soil.