Effects of Straw Incorporation and Tillage Depth on Soil Quality in Mollisol Profiles

ABSTRACT

Although improvements in soil quality under straw incorporation have been well documented, responses across soil profiles under different tillage depths remain unclear. To address this issue, a field experiment was established in 2011 in Mollisols with conventional tillage (20 cm depth) without straw (CT) and with straw (SCT), no tillage with straw mulching (SNT), inversion tillage (35 cm depth) with straw (SIT), and subsoil tillage (20–35 cm depth) with straw (SST). Compared with CT, nutrient contents, microbial biomass, enzyme activities, and phospholipid fatty acids (PLFAs) increased significantly in 0–60 cm soil layers in each of SCT, SIT, and SST treatments; microbial phosphorus limitation in 20–60 cm layers decreased; and a soil quality index (SQI) increased by 7.35%–45.45% in 0–60 cm layers. Yield of maize in SCT, SIT, and SST increased significantly by 8.62%–30.01%. Dominant factors affecting SQI varied by soil depth. Of soil chemical properties, these included available potassium and nitrogen (0–20 cm), NO ₃ ⁻ –N and dissolved organic carbon (DOC) (20–40 cm), microbial carbon and DOC (40–60 cm), and bacteria and G ⁺ , total PLFAs and G ⁺ , and G ⁺ and G ⁻ among PLFAs, respectively. Partial least‐squares path modeling suggested that straw incorporation directly affected soil chemical properties, reduced microbial phosphorus limitation, and increased the SQI from 0 to 20 cm. Straw incorporation with tillage jointly increased the SQI from 20 to 60 cm. This study provides feasible strategies for improving the quality of soil profiles and provides valuable insights for the sustainable agricultural management of Mollisols.