Degassing of greenhouse gases from groundwater under different irrigation methods: A neglected carbon source in agriculture

The degassing potential of supersaturated dissolved greenhouse gases (N2O, CO2, and CH4) in groundwater has often been overlooked as a source of emissions in irrigated agriculture. Quantifying the degassing potential and investigating measures are essential for agricultural carbon mitigation. This study estimated for the first time the direct greenhouse gas degassing potential from groundwater under different irrigation methods and explored mitigation strategies in the Guanzhong Basin, Northwest China. The results revealed that while short-term degassing potential from groundwater irrigation exceeds that reported for global inland waters and fertilized soils, the interannual degassing potential (13,819–52,163 t CO2-eq year−1) represents only 0.3–1.1 % of annual emissions from regional agricultural soils. The degassing potential exhibited a trend of over-surface drip irrigation (ODI) > surface drip irrigation (DI) > subsurface drip irrigation (SDI) > flood irrigation (FI) under equivalent irrigation volumes. Notably, SDI emerges as a promising strategy for concurrent water conservation and greenhouse gas mitigation. Switching from over-surface and surface drip irrigation to subsurface drip irrigation yields a reduction of 60.8 % and 46.3 % in carbon emissions per cubic meter of water saved, respectively. This study provides valuable insights for the development of sustainable irrigation practices and emphasizes the importance of integrating groundwater degassing potential into agricultural carbon budgets and emission mitigation strategies.