Nitrogen Mineralization Effects of Bacillus subtilis Combined with Straw Biochar in Dryland Soil
Biochar and microbial inoculants are widely used for agricultural soil amendment. To investigate the effects of different straw biochars and Bacillus subtilis inoculant, applied individually or combined, on nitrogen transformation in dryland soil, a 60-day laboratory incubation experiment was conducted with six treatments: control (CK), 4% rice straw biochar (S), 4% rapeseed straw biochar (Y), 4% rice straw biochar plus 5 mg/kg inoculant (SJ), 4% rapeseed straw biochar plus 5 mg/kg inoculant (YJ), and inoculant alone (J). Results showed that rice straw biochar significantly increased soil nitrate nitrogen content by 148.74%–152.68% compared to CK, enhancing nitrification. Combined application with inoculant further increased average net nitrogen mineralization rate by 77.28%–99.38%. Conversely, rapeseed straw biochar decreased nitrate nitrogen by 51.66%–57.61%, and combined application reduced net nitrogen mineralization rate by 82.07%–84.73%. Treatments S, Y, SJ, and YJ promoted microbial biomass nitrogen (MBN) synthesis, with S and Y increasing MBN by 2.02- and 2.20-fold over CK, respectively. Combined treatments further increased MBN by 103.26%–149.44% relative to single biochar treatments. These findings indicate that biochar type governs nitrification and net nitrogen mineralization, while combined application exerts synergistic effects on MBN. For comprehensive dryland soil improvement, YJ treatment is optimal, reducing inorganic nitrogen loss risk and enhancing microbial nitrogen activity.