Cultivation of grass reduces the leaching of nitrogen and organic carbon from peat fields
University of Oulu and Natural Resources Institute Finland (Luke) study in the NorPeat research field of the Ruukki experimental station of the Natural Resources Institute Finland (Luke), it was observed that farming methods affect leaching. Runoff during winter was also found to have a significant effect on the resulting leaching, contrary to what has been thought before, which is especially important if winters become milder in the future.
In the study, the concentrations of soil nutrients (nitrogen, phosphorus, organic carbon) and other substances harmful to water bodies (sulfur, iron, aluminum and acidity) were measured year-round from the runoff water of the peat field for three years (2018-2021). The amount of substances released from the field was examined in relation to the time of year, soil properties and the cultivation of the field in order to identify the most important factors affecting leaching.
The study found that when barley was grown on the field or the field was left bare for the winter, the leaching of nitrogen from the field was high, especially from the field blocks where the peat layer was thicker (more than 75 cm). Perennial grass cover, on the other hand, led to a significant reduction in nitrogen leaching and a decrease in phosphorus leaching. On the other hand, phosphorus leaching from Ruukki's NorPeat research field remained relatively low compared to the average leaching of Finnish fields. Despite the grass cover, the leaching of organic carbon, sulfur, acidity and iron was considerable. In terms of leaching, the most important period was the spring runoff, but the leaching was also high during the warm winter seasons.
About 10% of Finland's arable land is peat fields, but in Northern Ostrobothnia and Northern Finland the share is even 30% in some places. In most of these peat fields, forage grasses are cultivated for milk and beef production. This study showed that nitrogen and phosphorus and their leaching are not necessarily a significant problem in grass cultivation, but some other load factors may be. The ongoing research at Ruukki and the results it produces help farmers in developing better farming practices on peatlands to balance productivity and environmental impact.
The year-round monitoring of leaching in the Ruukki research field continues. In terms of the overall picture of the environmental effects of peat fields, it is important to study the combined effect of both leaching and greenhouse gas emissions. This will be investigated in the future at the NorPeat research field in a new experimental arrangement, where the groundwater level is controlled with the help of controlled sub-irrigation and the extra water provided by the water storage reservoir. Water management methods are used to mitigate greenhouse gas emissions while at the same time studying the leaching effects on water bodies.
Contact information:
Researcher Maarit Liimatainen, Natural Resources Institute Finland, Ruukki/Oulu, maarit.liimatainen@luke.fi, 050 301 9564
Researcher Timo Lötjönen, Natural Resources Institute Finland, Ruukki/Oulu, timo.lotjonen@luke.fi, 040 556 5926
PhD researcher Tung Pham, University of Oulu, Water, Energy and Environmental Research Unit, thanh.pham@oulu.fi, 046 884 9788
Additional information:
Ruukin tutkimusinfrastruktuuri | Luonnonvarakeskus (luke.fi)