Enhanced Sweet Sorghum Growth and Soil Quality in Coastal Saline–Alkali Soils Through Organic Acid-Containing Bio-Based Materials and Microbial Synergy

Coastal mudflats are characterized by high salinity and alkalinity, along with low mineral nutrient availability, making it challenging to achieve high biomass or effective yields when directly cultivating food or fodder crops. Exogenous complex saline soil amendments can enhance forage production, but their effects on soil salinity reduction and nutrient activation remain unclear. This study used pot experiments and laboratory analyses to investigate these effects. A 0.3% saline–alkali soil was treated with a combination of organic acids (fulvic acid and citric acid), bio-based materials (cow dung and pine needles), and beneficial microbial mixtures (Priestia megaterium + Trichoderma harzianum, Bacillus subtilis + Aspergillus niger, and Bacillus pumilus + Paecilomyces lilacinus). The organic acid bio-modifier significantly alleviated salinity stress in sweet sorghum, reducing soil salinity, increasing soil nutrient levels, enhancing root vigor and photosynthesis, and improving plant morphology, resulting in higher biomass yields. Among the factors tested, bio-based materials had the most pronounced effect. Citric acid, pine needles, Priestia megaterium, and Trichoderma harzianum enhanced sweet sorghum growth during the seedling stage, whereas fulvic acid, pine needles, Bacillus pumilus, and Paecilomyces lilacinus were more beneficial during the elongation stage.