Addition of softwood biochar did not reduce N₂O emissions or N leaching from peat soil in the short term

Drained agricultural peat soils pollute both the atmosphere and watercourses. Biochar has been observed to decrease greenhouse gas (GHG) emissions and nutrient loading in mineral soils. We studied effects of three biochar types with two application rates (10 and 30 Mg ha^-1) on GHG fluxes as well as N and P leaching on peat soil. Peat monoliths were drilled from a long-term cultivated field and were watered either slightly (five dry periods) or heavily (four rainfall periods) during an 11-month laboratory experiment with intact peat columns. The incubation of bare peat profiles enhanced peat decomposition leading to high CO₂ (up to 1300 mg CO₂ m^-2 h^-1) and N₂O emissions (even 10,000-50,000 μg N₂O m^-2 h^-1) and NO₃^--N leaching (even 300-700 mg L^-1) in all treatments. In the beginning of the experiment, the lower application rate of pine bark biochars increased N₂O emission compared to control, but otherwise none of the biochars or their application rates significantly affected gas fluxes or nutrient leaching. These results indicate that moderate softwood biochar application does not help to mitigate the environmental problems of agricultural peat soils. Higher application rate of biochar pyrolyzed at high temperature is recommended for further studies with peat soils.