Straw return with chemical fertilizer improves soil carbon pools and CO2 emissions by regulating stoichiometry

Abstract Straw return with chemical fertilizers is integral to improving soil quality and the sustainability of agricultural production. However, little is known about how straw return with chemical fertilizer application affects CO 2 emissions and carbon pools from the perspective of nutrient stoichiometry. We conducted a 2‐year (2020–2021) field experiment in a wheat–maize rotation system in silty clay loam to study the effects of straw return and fertilizer application on CO 2 emissions, soil carbon pools and yields by applying stoichiometry. A split‐plot experimental design was used (straw was main treatment, and fertilizer was the split‐plot treatment). The treatments were no straw return + no fertilizer (S 0 W), no straw return + mineral nitrogen fertilizer (S 0 N), no straw return + mineral nitrogen and phosphorus fertilizer (S 0 NP), straw return + no fertilizer (SW), straw return + mineral nitrogen fertilizer (SN) and straw return + mineral nitrogen and phosphorus fertilizer (SNP). The results indicated that, compared with S 0 W, the SNP treatment significantly increased soil organic carbon (SOC) storage by 17% and 13% in the 0–20 cm and 20–40 cm soil horizons, respectively. Additionally, compared with S 0 W, the SNP and SN treatments significantly increased the annual cumulative CO 2 emissions by 85% and 41%, respectively. Furthermore, the SNP and SN treatments significantly increased the annual yield by 61% and 38%, respectively, compared with S 0 W. Our results indicated that straw and fertilizer inputs reduced the C:N imbalance in the topsoil (0–20 cm), with fertilizer inputs showing a more pronounced effect. However, straw incorporation increased the C:N imbalance in subsoil (20–40 cm). Redundancy analysis (RDA) and structural equation models (SEM) suggested that 0–20 cm carbon‐phosphorus ratio (C:P) and nitrogen‐phosphorus ratio (N:P) could be significant predictors of annual yield and CO 2 emissions. In conclusion, straw and fertilizers enhanced soil nutrient effectiveness and reduced carbon mineralization in favour of SOC storage. However, the input of exogenous materials (straw and fertilizers) disrupted the soil ecological stoichiometric balance and stimulated microbial activity, leading to increased CO 2 emissions. Overall, this study provides theoretical guidance and scientific support for the green development of agriculture.