In 2024, the average nitrate level in the upper groundwater under derogation farms was well below the European norm. This is mainly due to the heavy rainfall in 2023 and 2024, which led to more nitrate being broken down in the soil and mixed with water. This is evident from the annual measurements by the RIVM on 300 agricultural businesses that use derogation.
Due to the alternation of very dry and very wet years, the nitrate levels under the farms have fluctuated greatly in recent years. Since 2017, there has been hardly any improvement in groundwater quality. In some regions, the amount of nitrate in the groundwater remains structurally too high. Therefore, efforts to improve groundwater quality are also needed on derogation farms.
What is derogation?
Since 2006, some agricultural businesses in the Netherlands have been allowed to use more animal manure on their land than the European Nitrate Directive prescribes. This applies to dairy farms with a lot of grassland, as grass easily breaks down nitrate. This relaxation is called derogation. The RIVM and Wageningen Social & Economic Research annually investigate how much manure these businesses use and how much nitrate is in the groundwater at 300 of the same derogation farms. The current regulation ends this year.
Alternation of dry and wet years causes fluctuations
The low amount of nitrate in the groundwater is due to the fact that in 2023 and 2024 more rainfall fell than average. When the groundwater is high, more nitrate is broken down in the soil and mixed with more water. The amount of nitrate in the groundwater is then lower. From 2018 to 2020, it was dry due to less rain. In those years, less nitrate was broken down in the soil, and the amount of nitrate in the groundwater was higher. 2025 has also been a dry year so far. This may affect water quality.
No improvement in the long term
Between 2006 and 2017, there was a clear decrease in the average amount of nitrate in the groundwater under derogation farms. This was due, for example, to increasingly smarter use of manure and a higher percentage of grassland. After 2016, the measurements show no clear decrease anymore, but strong fluctuations due to more extreme weather conditions.
Impact of drought on water quality
The RIVM conducted a study earlier this year on the regional effects of drought on the quality of groundwater in agricultural areas. This study showed that due to drought, more nitrogen in the form of nitrate remains in the soil. This is related to groundwater levels, which drop when it is dry for a long time. When there is little water in the soil, bacteria can break down nitrate less effectively. Plants also take up less nitrogen from the soil during drought.
After a dry period in the summer, the accumulated nitrate is washed away by rain in the autumn to the groundwater or surface water. However, if it also rains too little in the autumn and winter, the soil is too dry for that. It then takes longer for the accumulated nitrate to wash out to the groundwater or surface water. How quickly nitrate washes out after a dry period varies by soil type.