Plant nutrients in drainage water

The aim of the study is to assess the implementation and impact of the Estonian RDP interventions in the agri-environmental scheme, environmentally friendly management and organic farming on the aquatic environment, and to compare these with areas that have not joined any environment-related support scheme. During the hydrological survey, the flow of surface water and the use of fertilisers are assessed in an integrated manner. The study contributes to the Focus Area 4B (improving water management, including fertiliser and pesticide management).

Flows of drainage water shall be measured from the estuaries of the collector drains of the monitoring fields, and water samples shall be taken at an interval of two weeks. In the laboratory, the plant nutrient content of water samples shall be determined. The quality of drainage water is assessed on the basis of the nitrate ion concentration set out in the legislation, and, since drainage water flows to water bodies through collector ditches, it is also assessed in accordance with the requirements for these. Surface water quality is then compared against these requirements in three status classes. Based on field record book data, the total NPK balance for the monitoring fields is calculated using the OECD methodology. According to this methodology, plant nutrients removed from the field and returned with organic and mineral fertilisers, biologically bound nitrogen and seeds are taken into account when compiling the overall balance.

In 2022-2023, the average phosphorus leaching from the environmentally friendly management monitoring field was 0.07 kg/ha, from the non-environmental support field 0.12 kg/ha, and from the organic field 0.17 kg/ha per year. Compared to previous support periods (2007-2013 and 2014-2022), phosphorus leaching in the fields did not change.

If organic fertilisers are applied more than once during crop rotation, the total nutrient balance is also in large surplus, averaging 97-129 kg/ha of nitrogen for the period 2014-2023. This ensures soil fertility – both plant nutrients and organic carbon – but also indicates a risk of plant nutrient leaching.