The synergistic effect of Rhizophagus irregularis and Biochar on the growth of Switchgrass under sodium-saline-alkali stress: insights from soil mechanical property analysis.

Under saline-alkali stress conditions, inoculation with Rhizophagus irregularis or the application of biochar can both promote plant growth and improve soil physicochemical properties. However, the effects of their combined use on switchgrass growth and soil mechanical properties remain unclear. This study established four treatments: no Ri inoculation and no biochar addition (control, CK), biochar addition alone (BC), Rhizophagus irregularis inoculation alone (Ri), and their combination (RB). The aim was to investigate the effects of these treatments on the biomass, root morphology, and soil mechanical properties of switchgrass under saline-alkali stress. The results showed that compared to the CK treatment, the RB treatment significantly increased the root, stem, leaf, and total biomass of switchgrass by 67.55%, 74.76%, 117.31%, and 82.93%, respectively. Among all treatment groups, RB treatment significantly reduced soil bulk density, soil water-soluble sodium ions (Na⁺), soil exchangeable sodium percentage (ESP), and sodium adsorption ratio (SAR), while increasing soil porosity. Furthermore, RB treatment significantly improved infiltration rate and shear strength. Compared to the CK treatment, the stable infiltration rate and shear strength under 400 kPa vertical load increased by 70.69% and 22.5 kPa, respectively. In conclusion, the combination of Ri and biochar has the potential to improve soil mechanical properties and increase the biomass of switchgrass under saline-alkali stress.