Tillage With Straw Returning Promotes Soil Functional Microbiomes and Nitrogen Transformation to Increase Cotton Yield

The soil microbial community and its driven nitrogen (N) conversion are the key processes in cotton production. However, the responses of soil microbial communities to changes in farming practices (e.g., tillage and straw returning) remain unknown. This study sampled soil from the 0–20 cm and 20–40 cm layers of cotton fields under no-tillage (NT), tillage (T), no-tillage + straw returning (NT + SR), and tillage + straw returning (T + SR) practices, and high-throughput sequencing approach method was used to investigate the effects of farming practices on soil physicochemical properties, microbial community structure, and N metabolism pathways, as well as their associations with cotton yield. The survival rate (90.44% ± 0.90%) and yield (5314.0 ± 57.04 kg/ha) of cotton were highest under T + SR, and T improved cotton yield more effectively than SR. T increased the relative abundance of beneficial microorganisms and mediated their assimilation of ammonium nitrogen (NH+ 4-N) by improving the soil physical properties. In addition, the survival rate and yield of cotton were primarily related to the fungal communities and their pathways of assimilating NH+ 4-N because fungi had more complex and stable networks. The core microbiota contained most of the taxa that were significantly associated with N cycling genes and cotton yield, and even rare taxa could play an important role in microbial function. This study improves our understanding of the microbial N mechanism; T combined with SR can improve soil quality and establish healthy soil microflora (fungal-dominated type) to improve cotton production.