Potential contribution of water management practices under intensive crop production to climate-change-associated global warming

Optimizing water management practices to mitigate greenhouse gas (GHG) emissions in agroecosystems is of increasing interest under climate change. However, previous studies have focused more on paddy fields, little is known as to how water table management in subsurface drained fields or how irrigation practices in humid areas might affect the global warming potential (GWP). Drawing upon experimental data from four intensive crop production sites in Eastern Canada operating under different water management practices, the DeNitrification-DeComposition (DNDC) biogeochemical model was used to assess potential GHG emissions under twelve different sets of General Circulation Models coupled with Regional Climate Models (GCM-RCM) climate projections (2046–2075). Simulations showed that water table control/sub-irrigation and sprinkler irrigation might decrease GWP by allowing greater soil organic carbon (SOC) sequestration, despite increased N₂O and CO₂ emissions than non-irrigated systems. While drip irrigation marginally increased the SOC sequestration, GWP still increased because the C gains from the residues generated by the greater crop biomass were offset by increased CO₂ and N₂O emissions. Compared with surface drip irrigation, subsurface drip irrigation reduced the GWP by reducing N₂O emissions, as well as increasing crop yield and SOC stock. Although greater crop biomass was expected to return to soil under projected climate change, simulations showed a consistent increase in the GWP of tomato cropping system alone under climate change.