N2O emissions from fertilised peat soils under different water infiltration systems and groundwater levels

Agricultural use of peat soils results in large amounts of GHG emissions. Drainage of peat soils leads to mineralisation and thus CO₂ emissions. Wet conditions and copious amounts of carbon in fertilised peat soils generally also lead to high N₂O emissions. Water infiltration systems (WIS) could regulate the groundwater table (GWT), allowing agricultural use of these soils while at the same time reducing peat oxidation, CO₂-emissions and land subsidence. These changes to the groundwater will also affect N cycling processes yet it remains unclear how N₂O emissions will be affected. We hypothesised that 1) active drainage reduces N₂O emissions due to increased GWT stability, 2) a high GWT reduced N₂O emissions due to limited mineralisation and 3) active drainage prevents large peaks in N₂O emissions otherwise expected from fertilisers with a high mineral N content.  

In this study, we conducted two one-year field studies. In the first study (2024), we tested how N₂O emissions from peat soils were affected by grazing (urine and dung patches) and groundwater management (GWT and WIS). Treatments consisted of urine, dung patches and compaction or combinations thereof. These were laid out in a full factorial block design on 4 field parcels. In the second study (2025) we tested how different fertilisers affect N₂O emissions from peat soils under two GWTs. Treatments consisted of an unfertilised control, standard synthetic fertilisers (CAN and Urea), Urea + urease- or nitrification inhibitor, cattle slurry and manure derived bio-based fertilisers (liquid and solid fraction of cattle slurry and ammonium sulphate). In both studies N₂O emissions were measured using a closed chamber technique and gas monitor. In addition, grass yield and nitrogen uptake were recorded.

In 2024, N₂O emissions were highest from all treatments containing urine patches. N₂O emissions were highest from the field with a GWT. This could be explained by higher nitrogen mineralisation of peat, resulting in a high carbon availability for denitrification and thus increased N₂O fluxes. Surprisingly we did not see an effect of WIS on N₂O emissions. In 2025 GWT did not affect N₂O emissions, yet crop N uptake was higher from the field with a low GWT. Emissions from ammonium sulphate (1% of applied N) were highest compared to the other fertilisers. Surprisingly all other treatments resulted in similarly low N₂O emissions (<0.5%) with no effect of nitrification or urease inhibitor. Perhaps conditions such as temperature and precipitation inhibited emissions in 2025.