Mechanistic insights into the role of biochar C:N ratios in modulating greenhouse gas emissions and soil organic carbon fractions in contrasting soil types

Abstract Role of varying C:N ratios of biochar to enhance soil health and impacts across soil types remain inadequately understood. Therefore, this study aimed to elucidate the mechanisms of change in soil organic carbon (SOC) fractions and greenhouse gas (GHG) emissions under nitrogen‐enriched biochar (NB) application in sandy soil and loamy soil. A control (CK; without biochar) and four biochar types, including one pristine biochar (PB) and three types of NB (NB1, NB2, and NB3), were applied at two rates (20 t ha −1 [L1] and 40 t ha −1 [L2]). Biochar types and application levels significantly influenced CH₄ and CO₂ emissions. NB effectively reduced CH₄ while increased CO₂ emissions in both soil types. NB enhanced the SOC pools, which is primarily attributed to increased mineral‐associated and particulate SOC in both sandy and loamy soils. β‐glucosidase, cellobiohydrolase, and β‐xylosidase were significantly enhanced by NB, particularly at a higher application rate of biochar (L2) compared to CK, with more pronounced increases in loamy soil. Structural equation modeling showed that biochar types and application levels significantly influenced CH₄ and CO₂ emissions and SOC. The results provide valuable insights for guiding biochar applications aimed at reducing CO₂ and CH₄ emissions while improving soil fertility, with potential benefits for diverse agroecosystems and farming communities worldwide.