Soil moisture influences wheat yield by affecting root growth and the composition of microbial communities under drip fertigation

Water scarcity is a global problem constraining crop production worldwide. Winter wheat is northern China's biggest agricultural crop, but has a high water demand. The effects of different irrigation methods on water and N fertilizer productivity, crop yield, and root-soil-microbe interactions are not yet unclear. In this study, field experiments were conducted for two consecutive winter wheat seasons using four irrigation methods, namely surface drip irrigation (DI), subsurface drip irrigation (SDI), alternate partial rootzone irrigation (PRI), and flood irrigation (FP). The characteristics of soil conditions, root growth, microbial community structure, and grain yield were all measured, as well as water-to-N-use efficiency. Irrigation type significantly affected root growth, relative water content (RWC) in flag leaves, biomass and N content in stems, and the Shannon and ACE indices of bacteria and fungi. Compared with FP, SDI significantly increased root length, total projected area (TPA), and total surface area (TSA) by 121.1 %, 26.3 %, and 69.6 %, respectively. In contrast, DI significantly increased the weight, natural water content, and RWC of flag leaves by 28.8 %, 28.3 %, and 92.9 %, respectively. As compared to FP, DI increased LAI by 31.3 %, and PRI increased SPAD by 18.6 %. Drip irrigation increased the relative abundances of Actinobacteriota (dominant in bacteria, P<0.05) and Ascomycota (dominant in fungi, P<0.05). Soil moisture and root length were the main contributors that affected soil microbial communities. Correlation analysis revealed that increased moisture levels suppressed bacterial abundance, but improved fungal abundance. Additionally, root length, TPA, and TSA were positively correlated with yield. Unfortunately, the lowest yield was found in PRI during 2021 - 2022 in all treatments. Therefore, SDI improved root growth, the abundance of dominant bacterial communities, wheat yield, and water-N-use efficiency, which all contributed toward reducing irrigation water required for proper application.