Straw return and nitrogen-phosphorus fertilization coordinates crop yields, soil nutrient function and carbon emissions

Addressing the key challenge of reconciling agricultural intensification with ecological sustainability, this study investigated the synergistic effects of straw return and fertilization on winter wheat production systems in the Loess Plateau of China. Through a two-year field split-plot experiment, six treatments were established: control (S₀W), mineral nitrogen application (S₀N), nitrogen-phosphorus application (S₀NP), straw return (SW), straw return combined with nitrogen application (SN), and straw return combined with nitrogen-phosphorus application (SNP). This study systematically assessed their impacts on soil nutrient function index (NFI), ecological stoichiometry, crop yield, and CO₂ emissions. Our findings revealed that SNP and SN treatments elevated NFI by 258.29 % and 186.69 %, respectively, compared to S₀W. The SNP treatment achieved optimal yield enhancement (28.95-31.19 %) through optimization of NFI. In addition, compared to SW treatment, the SN treatment demonstrated a pronounced inhibitory effect on CO₂ emissions, achieving a reduction effect of 27.01 %. We applied the sustainability performance index (SPI) to assess the interdependence of yield-NFI-CO₂ emissions. The SNP obtained a better SPI (3.58) through the compensatory mechanism in the presence of increased CO₂ emissions. Partial least squares path model revealed that straw and fertilization directly increased carbon-nitrogen availability (P < 0.001) and indirectly enhanced NFI through improving physicochemical properties (P < 0.001). On the other hand, straw return combined with fertilization significantly reduced the dissolved organic carbon:nitrogen ratio and imbalanceCN. Enzyme stoichiometric analysis indicated that SNP treatment reduced vector length by 34.22-47.12 %, significantly alleviating carbon limitation. This mitigated competition between microorganisms and crops for resources, enhanced nutrient synchronization, and ultimately achieved synergistic improvements in productivity and NFI, but it also significantly increased CO₂ emissions. In conclusion, SNP treatment coordinates CO₂ emissions, crop productivity, and NFI through microbially mediated ecological stoichiometry. However, the long-term stability of these synergistic effects requires further validation through extended field trials under diverse agroecological conditions.