Effects of different exogenous additives on humification and microbial community during tomato straw composting process

The composting of agricultural organic wastes faces challenges such as prolonged maturation and inconsistent product quality, particularly for lignocellulose-rich materials like tomato straw. To address these limitations, this study investigated the effects of biochar, phosphogypsum, and calcium superphosphate as additives in tomato straw composting. These additives were selected for their documented roles in improving nutrient retention (biochar), pH regulation (phosphogypsum), and phosphorus supplementation (calcium superphosphate), which are critical for optimizing humification and microbial activity. To improve compost quality and reduce composting duration, four treatments were tested: T1 (tomato straw + 0.5% EM bacterial agent, control), T2 (tomato straw + 10% biochar + 0.5% EM bacterial agent), T3 (tomato straw + 10% calcium superphosphate + 0.5% EM bacterial agent), and T4 (tomato straw + 10% phosphogypsum + 0.5% EM bacterial agent). Results demonstrated that all additives prolonged the thermophilic phase and enhanced maturity compared to T1, with T2 (biochar) exhibiting the most pronounced effects. By the end of composting, T2 achieved the highest humic acid content increase (127.01%), along with the greatest organic matter and cellulose degradation (63% and 69.82%, respectively), significantly outperforming T1 (p < 0.05). Microbial analysis revealed Firmicutes, Actinobacteriota, and Proteobacteria as dominant phyla, while key genera driving decomposition included Bacillus, Weissella, Staphylococcus, and Halocella. Redundancy analysis and Mantel tests identified Corynebacterium as a critical genus linked to maturation. This study conclusively demonstrates that biochar significantly accelerates humification and organic matter degradation in tomato straw composting, providing a cost-effective strategy to enhance agricultural waste recycling. The findings highlight the importance of additive selection in optimizing microbial communities and functional outcomes during composting.