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 CO₂ 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 CO₂ 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 (S₀W), no straw return + mineral nitrogen fertilizer (S₀N), no straw return + mineral nitrogen and phosphorus fertilizer (S₀NP), 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 S₀W, 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 S₀W, the SNP and SN treatments significantly increased the annual cumulative CO₂ emissions by 85% and 41%, respectively. Furthermore, the SNP and SN treatments significantly increased the annual yield by 61% and 38%, respectively, compared with S₀W. 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 CO₂ 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 CO₂ emissions. Overall, this study provides theoretical guidance and scientific support for the green development of agriculture.