Impacts of changes in peat soils due to agricultural activities on greenhouse gas (especially N2O) emissions and their mitigations

Natural peatlands are a source of CH4 emission but a sink of CO2 and N2O. On the other hand, peatlands drained for agricultural use suppress CH4 emission but become a source of CO2 and N2O emissions. Drained peatland area accounts for 2% of the world's agricultural land, but its greenhouse gas (GHG) emissions account for 7% of global GHG emissions. Immediately after land clearing, N2O emission significantly increases due to nitrogen (N) fertilization. Furthermore, in tropical peatland fields that have been cultivated for a long term, annual N2O emission increased to 700 kg N ha-1 year-1. This shows that a successive process of organic matter decomposition, nitrification, and denitrification has been developed. On the other hand, in newly cleared oil palm plantations with proper water and fertilizer managements, both N2O and CO2 emissions decreased over time. Capillary risen from groundwater could increase water-filled pore space of the top layer, improve plant N uptake, and suppress organic matter decomposition. This is thought to have consumed surplus NO- 3-N, decomposed easily decomposable organic matter, and reduced N2O emission. Further research to verify its effectiveness over a long term will help to create sustainable peatland management.