Subsoiling tillage increased core microbiome associated with nitrogen fixation in the fallow season under rainfed maize monoculture

Abstract

Subsoiling tillage (ST) is a promising agronomy practice to improve soil physicochemical properties, soil microbial diversity during the crop growing season, and ultimately crop yield, but little is known about whether and how the ST practice will impact soil physicochemical properties and microbial communities in fallow season and their impacts on crop growth in next season. Here, a four-year continuous field experiment was conducted to compare the impacts of three tillage treatments, i.e., the ST, the no-tillage (NT), and the rotary tillage (RT), on soil physicochemical properties and microbial communities in maize fallow season. The results showed that compared with the RT treatment, the ST treatment improved maize yield by 2.3%, 4.2%, 11.4%, and 9.7% from 2018 to 2021, respectively, while there was no significant yield loss between the NT and RT. The ST treatment improved root biomass and soil available nitrogen by 25.1% and 34.0%, respectively, but scarcely impacted soil bulk density and water-filled pore space in comparison with the RT treatment in the maize fallow season in 2021. In addition, changes in root biomass further altered soil bacterial core microbiomes. Compared with the RT treatment, the ST treatment increased the relative abundance of core microbiomes related to nitrogen fixation and denitrification by 169.5% and 62.0%, respectively, but reduced the relative abundance of core microbiomes related to nitrification by 39.0%. The potential functional profile of core microbiomes predicted by the FAPROTAX database also showed that the ST treatment significantly improved nitrogen fixation and ureolysis by 115.9% and 346.9%, respectively, while decreased nitrification by 57.1% in comparison with the RT treatment. The results of the structural equation model showed that ST-induced changes in the function of nitrogen fixation improved soil available nitrogen content in the maize fallow season, which could supply nutrients for maize growth in the next growing season. Additionally, although the NT treatment improved microbial diversities in comparison with the RT and ST treatments, it reduced the relative abundance of microbiomes related to nitrogen cycling in the maize fallow season. These results indicate that the subsoiling tillage could increase the abundance of core microbiomes related to nitrogen fixation and mineralization, which increase soil available nitrogen content in the fallow season of maize cropping in the northeast of China.