Net global warming potential and carbon sequestration dynamics of deep straw incorporation with contrasting C:N...

Deep straw incorporation (DSI) has emerged as a promising soil amendment strategy for rehabilitating saline-alkaline lands, yet comprehensive quantification of its climate impacts-balancing carbon sequestration against greenhouse gas (GHG) emissions-remains limited. This study provides comprehensive estimates of net global warming potential (GWP) from a 4-year field experiment (2021-2024) examining DSI effects under varying straw C:N ratios in Northwest China's oasis agroecosystems. Three straw types-maize (C:N 60.2), wheat (C:N 42.8), and soybean (C:N 26.4)-were buried at 40-60 cm depth at rates of 0, 9.0, 13.5, and 18.0 Mg ha^-1. DSI significantly enhanced soil organic carbon (SOC) stocks by 8.2-22.4 Mg C ha^-1, with soybean straw achieving the highest sequestration rate of 5.6 ± 0.8 Mg C ha^-1 yr^-1. While anaerobic decomposition increased CH₄ emissions (1.8-4.2 kg CH₄ C ha^-1 yr^-1) and N₂O emissions (0.6-2.4 kg N₂O N ha^-1 yr^-1), net GWP revealed a critical temporal transition: positive values in Year 1 (+0.5 to +2.2 Mg CO₂-eq ha^-1 yr^-1) shifted to increasingly negative values by Years 3-4 (-1.6 to -5.8 Mg CO₂-eq ha^-1 yr^-1). The duration of this transition period was inversely related to straw C:N ratio: soybean straw (C:N 26.4) achieved net carbon sequestration within 1.2 years, compared to 2.4 years for maize straw (C:N 60.2). Soil moisture emerged as the dominant control on CH₄ production (R² = 0.76, P < 0.001), with emissions increasing exponentially above 65 % water-filled pore space. The optimal configuration-13.5 Mg ha^-1 soybean straw-delivered the most rapid climate benefit transition while achieving 52 % yield enhancement and 25-35 % improvement in nitrogen use efficiency. These findings demonstrate that DSI, despite an initial period of net GHG emissions, transitions to function as a sustained carbon sink, providing critical insights for designing climate-smart agricultural practices in water-limited arid regions.