Abstract:To comparatively explore the effects of the application of biochar and plant growth-promoting rhizobacteria (Bacillus subtilis and Bacillus mucilaginosus, PGPR) on the soil aggregate content, soil aggregate stability, and soil moisture of the silty loam soil of the mountain apple orchard on the loess hilly region, we adopted field research and set four treatments:65 t/hm2 biochar (BC), 20 t/hm2 B. subtilis (PGBS), 20 t/hm2 B. mucilaginosus (PGBM), and control (CK). The aggregate content of different soil particle size were examined by wet sieving method, and the mean weight diameter (MWD), geometric mean diameter (GMD), and fractal dimension (D) of water-stable aggregates were calculated. The results showed that compared with CK, the soil organic carbon (SOC) increased by 18.04%~206.91%, and the total nitrogen (TN) content increased by 6.11%~66.56% in BC, PGBS, and PGBM treatment. The content of > 0.25 mm aggregates in the 0—60 cm soil layer increased significantly in treatment BC, PGBS, and PGBM. Compared with CK, the fractal dimension D was decreased and the MWD and GMD were increased in different treatments, of which the order of magnitude was PGBS>PGBM>BC and this indicated that the application of amendments can increase the stability of soil aggregates. The saturated hydraulic conductivity and soil water content of the 0—60 cm soil in each treatment were increased. The application of PGPR and biochar could significantly increase the content of soil organic carbon and total nitrogen, enhance the stability of soil structure, and increase soil saturated hydraulic conductivity and water content. The improvements of soil organic carbon and total nitrogen content by biochar treatment was better than that by plant growth-promoting rhizobacteria, while the plant growth-promoting rhizobacteria treatment improved the stability of soil structure better.