Drivers of soil quality and maize yield under long-term tillage and straw incorporation in Mollisols

Proper tillage combined with straw management is crucial for maintaining agroecosystem sustainability and crop yield, especially under intensified agricultural activities. However, the optimal depth for tillage in combination with straw incorporation remains unclear. To address this, we established a field experiment in 2011 in Mollisols with five treatments: conventional tillage (CT, tillage depth 20 cm), no-tillage combined with straw return (SNT), conventional tillage combined with straw return (SCT), inversion tillage combined with straw return (SIT, tillage depth 35 cm), and subsoil tillage combined with straw return (SST, straw depth 20-35 cm). We assessed the effects of these treatments on soil quality by evaluating the Soil Physical Property Index (SPI), Soil Chemical Property Index (SCI), and Soil Microbial Property Index (SMI) in relation to the Soil Quality Index (SQI) and crop yield. Our findings shown that tillage combined with straw return significantly improved soil properties. Compared to the CT, SNT, and SST treatments, the SCT and SIT treatments increased SPI and SQI in the 0-20 cm soil layer by 43.9-845.4 %. While the SIT and SST treatments enhanced SPI, SCI, and SMI in the 20-35 cm soil layer by 69.2-307.7 % more than the CT, SNT, and SCT treatments. Among all treatments, SIT treatment resulted in the highest SPI, SCI, and SMI in the 0-35 cm soil layer. Additionally, SQI and maize yield under the SIT treatment were 11.7-140.5 % and 15.6-78.0 % higher, respectively, compared to other treatments. Linear regression analysis revealed that SPI in all layers had a significant impact on maize yield, while SCI and SMI were significantly correlated with yield only in the 20-35 cm layer (P < 0.05). SPI's contribution to maize yield was 18.6-156.8 % higher than that of SCI and SMI. Partial least-squares path modeling identified SPI as a direct influence on SMI and SCI, making it the largest driver indirectly improving SQI and maize yield in Mollisols. Therefore, SIT treatment is a highly effective soil management practice for improving soil quality and crop yields in the Mollisols region. Our study provides guidance for enhancing soil environmental quality and designing sustainable agricultural policies in the Mollisols region and other arable soils.