Bioremediation of Saline-Alkali Soil Using a Waste Biomass-Functional Microorganism Composite Amendment and Preliminary Multi-Crop Field Validation

Soil salinization threatens crop production; however, in multi-crop field systems, evidence for the effectiveness of waste biomass-functional microorganism composite amendments remains limited. Here, we developed a composite microbial soil conditioner (F2) using pine needles and crushed corn cobs as carriers combined with salt-tolerant strains Bacillus subtilis (K1), Azotobacter chroococcum (Y1), and Bacillus gelatinus (J3) to remediate moderately saline-alkali soil from central Gansu (pH 8.36 ± 0.18; EC 1658 ± 55.24 μS·cm−1). Saturation screening identified an optimal carrier ratio of pine needles:corn cobs = 1:2 and an inoculum ratio of K1:Y1:J3 = 1:2:1. In pot experiments, F2 increased soil organic matter and water-holding capacity, enhanced alkaline phosphatase, urease, and sucrase activities, and significantly reduced soil pH and EC. Maize seedling height and chlorophyll content increased by 53.87% and 38.88%, respectively. Amplicon-based microbiome profiling indicated enrichment of beneficial microbial taxa and strengthened primary metabolic functions under F2. Field validation across five crops (flax, potato, edible sunflower, sorghum, and maize) showed consistent growth and yield-related improvements. Overall, these results demonstrate that the biomass–microbe composite amendment effectively alleviates saline-alkali constraints by jointly improving soil properties, microbial functions, and crop performance.