Microbial valorization of mung bean residues into a slow-release multi-nutrient biofertilizer via EPS-mediated...

Agricultural biomass valorization is a critical component of the circular bioeconomy for improving resource efficiency and sustainable nutrient management. Large quantities of mung bean (Vigna radiata) plant residues are generated after harvest and are often burned or discarded, resulting in environmental pollution and nutrient loss. Here, we developed a microbially mediated strategy to convert mung bean plant residues (MBPR) into a slow-release multi-nutrient biofertilizer through lignocellulose biodegradation and phosphorus biomineralization. Lignocellulose-degrading bacteria (Paenibacillus glycanilyticus, Metabacillus endolithicus, and Pseudomonas citronellolis) were applied during composting, significantly accelerating biomass decomposition and compost maturity. The C/N ratio decreased from 39.86 in untreated residues to 17.73 and 19.01 within 40 days in P. glycanilyticus and P. citronellolis treatments, respectively. All strains produced extracellular polymeric substances (EPS; 1.29-1.32 g/L), which promoted Ca²⁺/Mg²⁺ interactions and induced phosphate mineral nucleation. X-ray diffraction confirmed the formation of magnesium ammonium phosphate and Ca/K-based pyrophosphate phases. Nutrient leaching was substantially reduced, with the lowest losses observed in the P. glycanilyticus treatment (K: 0.31%, P: 13.61%, Mg: 14.26%). The resulting fertilizer significantly enhanced mung bean growth. These findings demonstrate that EPS-mediated biomineralization enables MBPR valorization into a dual-phase nutrient system that improves nutrient availability while maintaining long-term stability, offering a sustainable pathway for recycling agricultural waste and developing slow-release fertilizers.