The increasing reliance on chemical fertilizers has raised environmental concerns and highlighted the need for sustainable alternatives. This study aimed to (i) optimize the carrier-to-substrate ratios and moisture content during composting with potassium-solubilizing purple nonsulfur bacteria (K-PNSB) and (ii) evaluate the growth-promoting effect of the optimized biofertilizer on maize seedlings. Three K-PNSB strains (Cereibacter sphaeroides M-Sl-09, Rhodopseudomonas thermotolerans M-So-11, and Rhodopseudomonas palustris M-So-14) were used. Composting experiments were conducted using different carrier-to-substrate ratios and moisture levels with K-PNSB inoculation. Compost quality was assessed through nutrient dynamics, bacterial density, and physicochemical properties over four weeks. The results showed that the 1:1:3 substrate ratio combined with 50–60% moisture content consistently enhanced K solubilization, bacterial survival, and compost maturity indicators. Application of the optimized biofertilizer improved maize growth traits compared with the non-inoculated control. These findings demonstrate that controlling material ratios and moisture content improves compost quality and plant growth performance, providing a sustainable alternative to chemical fertilizers. This study provides a practical framework for developing sustainable K-solubilizing biofertilizers from agricultural residues.
Nguyen et al. (Fri,) studied this question.