Effects of Four-Year Oilseed Flax Rotations on the Soil Bacterial Community in a Semi-Arid Agroecosystem

Crop rotation aims to improve the sustainability and production efficiency of agricultural ecosystems, especially as demands for food and energy continue to increase. However, the regulation of soil microbial communities using crop rotation with oilseed flax and its relationship with key soil physicochemical driving factors are still not clear. In order to investigate this matter, we carried out a field study lasting four years involving various crop rotation sequences including FWPF, FPFW, PFWF, FWFP, ContF, and ContF1. In addition to evaluating soil physicochemical parameters, we employed Illumina high-throughput sequencing technology to explore the structure and variety of soil microbial communities. The findings indicated a notable rise in pH value with the FPFW treatment in contrast to other treatments, along with significant increases in AP, MBC, MBN, and qSMBC compared to ContF. The number of OTUs in the FPFW, WFPF, FPFW, and PFWF treatments was significantly increased by 4.10–11.11% compared to ContF (p < 0.05). The presence of Actinobacteria and Acidobacteria was greatly impacted by the FPFW treatment, whereas the presence of Actinobacteria and Chloroflexi was notably influenced by the ContF treatment. The soil bacterial community was primarily influenced by TC, pH, and NO3−-N according to correlation analysis. Specifically, the FPFW therapy notably raised the soil pH level while lowering the TC level. Furthermore, the FPFW therapy led to a notable rise in the proportion of Acidobacteria and a significant decline in the proportion of Actinobacteria. These findings provide important theoretical support for using FPFW rotation to regulate soil microbial communities and solve the problems of continuous cropping.