Biochar Simultaneously Reduces Nutrient Leaching and Greenhouse Gas Emissions in Restored Wetland Soils

Organic soil amendments such as biochar and compost are thought to improve soil development, but it is unclear whether they affect nutrient leaching and greenhouse gas emissions. Using mesocosms, we investigated the effects of biochar and compost on nutrient leaching and greenhouse gas emissions across varying hydrologic regimes. Increased biochar decreased nutrient leaching and greenhouse gas emissions: the highest application rate (10% wt/wt) decreased cumulative phosphate leaching by 63% (SE 1.4), ammonium leaching by 65% (SE 0.8) and nitrate leaching by 92% (SE 0.3). Likewise, 10% biochar application decreased cumulative methane emissions by 92% (SE 3.7), carbon dioxide emissions by 48% (SE 7.0), and nitrous oxide emissions by 89% (SE 4.1). Biochar effects varied with hydrology for each greenhouse gas: stronger reductions in methane and nitrous oxide emissions were observed under waterlogged conditions, whereas stronger reductions in carbon dioxide emissions were observed at field capacity. In contrast with biochar, compost was the largest contributor to nutrient leaching and greenhouse gas emissions. These results suggest that biochar is most effective in soils with episodic flooding and drying rather than continuous flooding, and that compost should be avoided. We conclude that biochar can promote desirable functions simultaneously in restored wetland soils.