Objective Effects of tilling and straw-returning on the physicochemical properties and microbial communities of soil on a cotton-potato rotating cultivation field were studied.

Methods Four treatments were established in the potato-cotton rotation field, including no-tillage (NT), no-tillage with straw returning (NTS), rotary tillage (T), and rotary tillage with straw returning (TS). Soil physicochemical characteristics, enzyme activities and rhizosphere soil microbial community structure were determined. Redundancy Analysis (RDA) was adopted to identify key factors driving the variation of microbial community structure.

Results Comparing to NT, by returning the spent straws to the field, NTS significantly increased the contents of soil hydrolyzable nitrogen to 244.66 mg·kg⁻¹ and available potassium to 411.00 mg·kg⁻¹. Similarly, TS significantly increased available phosphorus to 388.73 mg·kg⁻¹ and total phosphorus to 1.82 g·kg⁻¹. Additionally, the treatment significantly reduced the bulk density, enhanced the porosity, and increased the water-holding capacity of the soil at cotton boll stage. But straw-returning did not significantly affect the enzyme activity in soil. However, T significantly heightened the catalase activity at cotton seedling stage and the sucrose enzyme activity at boll stage. Microbiologically, NTS significantly raised the fungal Shannon diversity, while TS significantly increased the taxa of fungi like Aspergillus that related to organic matter degradation. The microbial community became significantly abundant with Proteobacteria and Bacteroidetes, as affected by the changes in organic matter and phosphorus content in soil when straws were returned in NTS and TS. RDA and network analysis revealed that soil microbial community structure was co-driven by soil organic matter, pH and phosphorus content. The bacterial community possessed higher network connectivity, clustering degree and interaction complexity than fungal community, presenting stronger interspecific correlation and functional synergy.

Conclusion TS mode has comprehensive advantages in improving soil physical properties, promoting phosphorus supply and maintaining soil microecological balance. NTS mode saves labor and energy and optimizes nitrogen and potassium nutrition. Appropriate tillage and straw returning combinations can be selected according to local soil conditions and economic demands in practical cotton cultivation.