Abstract
BACKGROUND AND AIMS: Biochar is a widely recognized amendment for augmenting crop productivity and mitigating greenhouse gas (GHG) emissions, particularly in degraded soil. However, optimal biochar rate and their mechanisms remain uncertain across different salinity severities. METHODS: To address this knowledge gap, a two crop seasons experiment was conducted from 2022 to 2023 on mildly (S1) and moderately (S2) saline soils, employing four biochar application rates: 0, 10, 20, and 40 t·ha(-1). This study systematically evaluated the effects of biochar on crop yield, GHG emissions, and soil organic carbon. RESULTS: The results revealed significant disparities in GHG emissions and carbon sequestration capacity between the two soil salinity levels. Under identical treatments, total soil CO(2) emissions in S2 were 14.70%-26.99% lower than those in S1, whereas total soil N(2)O, CH(4) emissions were elevated by 37.94%-61.04% and 34.41%-94.74%, respectively. For every 0.5 g·kg(-1) increase in soil salinity, the soil organic carbon storage (SOCS) declined by 6.09%. Biochar application substantially increased crop yield (↑14.51%-30.65%) and SOCS (↑218.51%-404.52%) while concurrently mitigating global warming potential (GWP, ↓10.08%-24.12%), greenhouse gas intensity (GHGI, ↓20.75%-41.84%), and net greenhouse gas emissions (NGHGE, ↓205.83%-437.14%) (P< 0.01). Pearson's correlation analysis demonstrated significant negative correlations between SOC/SOCS and GHG emission indicators as well as a strong relationship between crop yield and GHGI. CONCLUSION: Regression optimization modeling identified the optimal biochar application rates as 26.67 t·ha(-1) for S1 and 30.82 t·ha(-1) for S2, which achieved the most favorable balance between agricultural productivity and environmental benefits. This study demonstrates that appropriate biochar application can significantly enhance the carbon sink function of saline-alkali farmlands, reduce climate risks, and provide a promising strategy for sustainable agriculture in marginal lands.