Greenhouse Gas Emissions from Soils Amended with Cornstalk Biochar at Different Addition Ratios

Biochar addition has been recommended as a potential strategy for mitigating climate change. However, the number of studies simultaneously investigating the effects of biochar addition on CO₂, N₂O and CH₄ emissions and sequentially global warming potential (GWP) is limited, especially concerning its effect on native soil organic carbon (SOC) mineralization. An incubation experiment was conducted to investigate soil physicochemical properties, CO₂, N₂O and CH₄ emissions and GWP in the treatments with 0% (CK), 1% (BC1) and 4% (BC4) cornstalk biochar additions, and clarify the priming effect of biochar on native SOC mineralization by the ¹³C tracer technique. Generally, biochar addition increased soil pH, cation exchange capacity, SOC and total nitrogen, but decreased NH₄⁺-N and NO₃^--N. Compared with CK, BC1 and BC4 significantly reduced CO₂ emissions by 20.7% and 28.0%, and reduced N₂O emissions by 25.6% and 95.4%, respectively. However, BC1 significantly reduced CH₄ emission by 43.6%, and BC4 increased CH₄ emission by 19.3%. BC1 and BC4 significantly reduced the GWP by 20.8% and 29.3%, but there was no significant difference between them. Biochar addition had a negative priming effect on native SOC mineralization, which was the reason for the CO₂ emission reduction. The negative priming effect of biochar was attributed to the physical protection of native SOC by promoting microaggregate formation and preferentially using soluble organic carbon in biochar. The N₂O emission decrease was rooted in the reduction of nitrification and denitrification substrates by promoting the microbial assimilation of inorganic nitrogen. The inconsistency of CH₄ emissions was attributed to the different relative contributions of CH₄ production and oxidation under different biochar addition ratios. Our study suggests that 1% should be a more reasonable biochar addition ratio for mitigating greenhouse gas emissions in sandy loam, and emphasizes that it is necessary to furtherly investigate nitrogen primary transformation rates and the relative contributions of CH₄ production and oxidation by the ¹⁵N and ¹³C technique, which is helpful for comprehensively understanding the effect mechanisms of biochar addition on greenhouse gas emissions.