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

Abstract

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 NO₃^--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.