Nitrogen losses from drained temperate agricultural peatland after mineral soil coverage

Drainage for agriculture induces peatland decomposition, subsidence, and nitrogen (N) losess, thereby contributing to climate change. In order to maintain the productivity of agricultural managed peatland, and to counteract soil subsidence, mineral soil coverage is becoming an increasingly used practice in Switzerland and other European countries. Mineral soil coverage may change the N balance from the corronsponding organic soil. To explore the effect of this practice on the N flow within the plant – soil system and the N loss, we carried out a field experiment on a peatland in the Swiss Rhine Valley that was managed as an intensive meadow. The peatland was divided into two parts, either without (Ref) or with mineral soil coverage, thickness ~ 40 cm (Cov). In this experiment, ¹⁵NH₄¹⁵NO₃ were applied on field plots to follow the recovery of ¹⁵N in grass, root, and soil over 11 months. The ¹⁵N that was not recovered was designated as lost via leaching or gaseous emissions. Soil N mineralization was measured in a laboratory incubation. And the gaseous N loss as N₂O was determined by automatic time integrating chamber systems (ATIC) over two years. The experimental results showed that the total ¹⁵N loss from Cov was lower (p < 0.05) than from Ref, even though plant ¹⁵N uptake did not vary between the two sites. The lower net N loss from the Cov site was accompanied by higher soil ¹⁵N retention in the soil. The laboratory incubation revealed a ~2 times higher specific N release per unit soil N at Cov than at Ref, suggesting a faster SOM turnover rate at Cov. Regarding the N loss as N₂O, emissions from Ref were at the upper end of previously measured fluxes in drained peatland. In contrast, N₂O emissions from Cov were reduced by a factor of nine over two years. Overall, the mineral soil cover increased the retention of fertilizer-N in the soil, thus reducing the system N losses, especially N loss as N₂O emissions. Our results indicate agricultural production on drained peatland is less harmful to the environment with mineral soil coverage than using drained peatland directly.