Straw incorporation plus biochar addition improved the soil quality index focused on enhancing crop yield and alleviating global warming potential

The stimulated N2O emission by straw incorporation (S1) is adverse to mitigating global warming potential (GWP). Thus, this study advocated an optimal straw-based system, i.e. S1 plus biochar (SB), to mitigate the straw-induced N2O emission and further promote soil organic carbon (SOC) sequestration. Moreover, this study addressed research gap on quantification of soil quality focused on enhancing yield and alleviating GWP. Greenhouse gas emission intensity (GHGI) was used to relate yield with GWP. A field experiment was conducted to investigate the response of overall soil quality to S1, SB and no straw inputs (S0) under two nitrogen rates (routine rate [N1] and 70% of routine rate [N0.7]). To comprehensively evaluate soil quality, a wide range of soil physical, chemical, biological and ecological properties closely related to yield and GHGI were measured and integrated into a soil quality index (SQI). Although both S1 and SB enhanced the SQI, the SB achieved the highest SQI under N1 rate. Firstly, this is because N1-SB significantly mitigated the straw-induced N2O emission, associated with the declined soil inorganic nitrogen (SIN) and dissolved organic carbon (DOC) contents. Secondly, N1-SB greatly enhanced SOC sequestration, mainly attributed to the increased ratio of microbial biomass carbon to microbial biomass nitrogen (MBC/MBN) and decreased microbial quotient (MBC/soil organic carbon and MBN/total nitrogen), implying the lower efficiency of soil microorganisms to utilize soil organic matter. Lastly, N1-SB markedly increased maize yield in 2019 compared to S0. Overall, the highest SQI for N1-SB was ascribed to the higher soil quality scores in labile nitrogen/total nitrogen (LN/TN) and MBC/MBN, and lower soil quality scores in SIN and DOC.