Objective The aim was to explore the characteristics and influencing factors of soil bacterial community in the plough layer of sunflower and corn fields in the non-growing season after autumn harvest in Hetao Irrigation District of Inner Mongolia, and to provide basic data for further understanding the mechanism of soil bacterial community construction in local farmland.

Method Soil samples were collected from 0 ~ 10 cm, 10 ~ 20 cm and below 20 ~ 30 cm soil layers of sunflower and corn fields in Hetao Irrigation District in early October (after the end of the growing season). The composition and diversity of soil bacterial communities were determined by 16 S rRNA high-throughput sequencing technology. The zero model method based on βNTI and RCbray index was used to distinguish the bacterial community construction process, and the effects of soil water content (SWC), bulk density (BD), total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC) and other physical and chemical properties on soil microbial community construction were analyzed.

Result ① With the increase of soil depth, the relative abundance of soil bacteria in most sunflower and corn fields increased, and the community diversity decreased. The dominant bacteria in soil were Chloroflex, Acidobacteria, Proteobacteria and Actinobacteriota. ② The stability of soil bacterial community in different depths of sunflower and maize farmland was 20 ~ 30 cm > 0 ~ 10 cm > 10 ~ 20 cm and 10 ~ 20 cm > 20 ~ 30 cm > 0 ~ 10 cm, respectively, and the spatial network relationship of soil bacterial community was dominated by cooperation. ③ The construction of soil bacterial community in the plough layer of sunflower farmland was controlled by both random process and deterministic process, while the construction of soil bacterial community in the plough layer of maize farmland was all controlled by random process and dominated by diffusion limitation process. ④ The results of Mantel test showed that although SWC, BD, TN and C: N had significant effects on the soil bacterial community structure of sunflower and maize farmland. TOC and TP were the main factors affecting the construction of soil bacterial community in the plough layer of the two crops.

Conclusion In the non-crop growing season (October) of Hetao Irrigation District, Inner Mongolia, the composition of soil bacterial communities in different depths of sunflower and maize farmland was similar, but the relative abundance was significantly different, and the bacterial community construction was dominated by the diffusion restriction mechanism in the random process. The difference of TOC and TP between different soil layers is the key factor affecting the transformation of bacterial community construction between random process and deterministic process.