Enhancing the Efficiency of Compost Pellets for Organic Farming via Beneficial Microbial Enrichment

ABSTRACT Introduction Compost from organic fraction of municipal solid waste (OFMSW) is a valuable organic amendment for organic farming; however, its low immediate nutrient availability requires the application of large amounts to meet crop demands. Although pelletisation improves handling and reduces the volume rate, this process decreases the viability of beneficial microorganisms and slows down nutrient mineralisation. To counteract these limitations, this study evaluated the enrichment of compost pellets with a consortium of plant growth‐promoting rhizobacteria (PGPR), accelerating organic matter decomposition and enhancing nutrient availability. Materials and Methods A microcosm experiment was conducted to test three types of compost pellet in acidic and basic soils cultivated with tomato ( Solanum lycopersicum L.) and broccoli ( Brassica oleracea L. var. italica Plenck); the three pellet types differed in the origin of the OFMSW and in the composting duration. The pellets were tested both in their original state and when enriched with a bacterial consortium comprising Bacillus mojavensis , Azotobacter chroococcum , and Proteus cibi . Crop biomass production, soil and plant nutrient dynamics, nutrient use efficiency, soil respiration, and structure, diversity, and potential functionality of soil microbiome were assessed. In addition, microbial load resulting from the enrichment process was assessed. Results Microbial enrichment successfully restored and increased the bacterial load reduced by the pelletisation process. Enriched compost pellets significantly increased crop biomass and improved nutrient use and recovery efficiencies compared with non‐enriched pellets and the control without compost addition. Furthermore, microbial enrichment promoted more diverse and functionally active soil communities, increasing the abundance of beneficial taxa involved in nutrient mineralisation and biocontrol while reducing potentially pathogenic microorganisms. Conclusion Overall, these results demonstrate that microbial enrichment of OFMSW compost pellets mitigates the drawbacks associated with pelletisation, enhances nutrient availability, and improves crop performance, highlighting its potential as a promising strategy for organic farming, pending validation under field conditions.