Optimizing soybean production and emission reduction through biogas slurry substitution and straw incorporation: A five-year field study in northeast China's black soil region

Abstract

To address the dual challenges of enhancing soybean yield and mitigating greenhouse gas (GHG) emissions in sustainable agriculture, this five-year field study (2020–2024) in Northeast China's black soil region evaluated the synergistic effects of biogas slurry substitution (0–100 % nitrogen replacement) and straw incorporation methods (deep ploughing vs. surface covering) on soil carbon-nitrogen dynamics, GHG emissions, and agronomic performance. Results demonstrated that a 75 % biogas slurry substitution (R3) combined with deep ploughing maximized soybean yield (4.24–18.36 % increase over conventional nitrogen fertilization) while significantly improving soil organic carbon (SOC, +10.52–25.72 %), dissolved organic carbon (DOC, +1.36–5.58 %), and nitrogen availability (NO₃^--N: +11.47–25.27 %; NH₄⁺-N: +10.04–22.74 %). Crucially, deep ploughing with R3 reduced GHG emissions by 4.29–18.63 % (CO₂, N₂O, CH₄), global warming potential (GWP) by 8.96–17.63 %, and emission intensity (GHGI) by 9.26–16.29 % compared to surface covering. Structural equation modeling revealed that elevated SOC and NO₃^--N mediated the trade-off between yield enhancement and emission reduction. These findings highlight that integrating 75 % biogas slurry substitution with deep straw incorporation optimizes the carbon-nitrogen cycle, achieving synergistic yield growth (13.31 % maximum), carbon sequestration (SOC, +25.72 %), and GHG mitigation (CH_4, −18.63 %), providing a transformative strategy for climate-resilient soybean production in temperate agroecosystems.