Regulation of CH4 and N2O Emissions by Biochar Application in a Salt-Affected Sorghum Farmland

The ameliorative mechanism of biochar in reducing soil greenhouse gas emissions in arid saline farmland remains unclear. A two-year field study in sorghum farmland in China’s Hetao Irrigation District was conducted to assess the influence of corn straw-derived biochar on GHG emissions and explore the role of soil physicochemical properties in regulating GHG fluxes. Four different biochar application rates were tested: 0 (CK), 15 (C15), 30 (C30), and 45 t hm−2 (C45). Compared to CK, C15 reduced CH4 emissions by 15.2% and seasonal CH4 flux by 77.0%. The N2O flux followed CK > C45 > C30 > C15 from 2021 to 2022. C15 and C30 significantly decreased GWP, mitigating GHG emission intensity. Biochar application enhanced sorghum grain yield. Soil temperature was the primary determinant of CH4 flux (total effect = 0.92). In the second year, biochar’s influence on CH4 emissions increased by 0.76. Multivariate SEM identified soil moisture (total effect = −0.72) and soil temperature (total effect = −0.70) as primary negative regulators of N2O fluxes. C40 lead to salt accumulation, which increases CH4 emissions but inhibits N2O emissions. Averaged over two years, GWP under C15 and C30 decreased by 76.5–106.7% and 5.3–56.1%, respectively, compared to CK. Overall, the application of biochar at a rate of 15 t hm−2 significantly reduced CH4 and N2O emissions and increased sorghum yield.