Improving soil properties and Sesbania growth through combined organic amendment strategies in a coastal saline-alkali soil

Improving the quality of degraded coastal saline-alkali soil and promoting plant growth are key challenges in the restoration of ecological functions in coastal regions. Organic ameliorants such as effective microbial (EM) agent, biochar, and organic compost have been proposed as sustainable solutions, but limited research has explored the combined effects of these amendments. This study investigates five organic improvement strategies: individual applications of EM, corn straw biochar (CSB), and sewage sludge-reed straw compost (COM), along with combined treatments of CSB + EM and COM + EM, on Sesbania growth in a pot experiment. The results demonstrated that, compared to the separate applications, the combined strategies (CSB + EM and COM + EM) exhibited a greater improvement in Sesbania growth; for instance, the plant dry weight was 4.61-12.1 times that of the control. The improved plant growth was linked to enhanced nutrient uptake and changes in soil properties. The combined strategies, particularly COM + EM, resulted in greater decreases in soil pH (decreased by 2.79%-3.49% compared to the control) and better improvements in soil nutrient content, quantity and quality of dissolved organic matter, microbial community diversity, and the abundance of plant growth-promoting rhizobacteria (PGPR), e.g., Bacillus. Spearman correlation and structural equation modeling confirmed that these soil improvements directly contributed to enhanced plant nutrient uptake. Overall, these findings suggest that combined strategies of COM + EM and CSB + EM, particularly the former, are highly effective for the remediation of coastal saline-alkali soils, offering a promising approach for improving soil fertility and plant productivity in degraded coastal ecosystems.