Biochar as a biofertilizer carrier: Synergistic effects on inoculant survival and native microbial communities in Mediterranean soils

Abstract

Biochar has emerged as a promising carrier for microbial inoculants, yet its capacity to enhance inoculant persistence while preserving native soil microbial communities remains insufficiently documented. This study evaluated an olive-pomace-derived biochar as a carrier for Bacillus velezensis and Trichoderma virens in a Mediterranean Cambisol under controlled conditions. Biochar supported high initial microbial loadings (>10⁸ CFU or spores g⁻¹ biochar), strong short-term viability (76–88%), and clear colonization of pore surfaces as observed by scanning electron microscopy. Following a 30-day pot incubation, biochar-based inoculation enhanced microbial persistence compared with direct soil application, maintaining recoverable inoculant populations close to or above initial levels. Findings revealed that biochar maintained community-level structural and functional patterns at the resolution detectable by fingerprinting and metabolic profiling approaches. These results suggest that biochar functioned primarily as a physical carrier, providing protected microsites that may have contributed to the stabilization of introduced microorganisms while maintaining overall soil functional diversity. Our findings demonstrate that olive-pomace biochar can be valorized as an effective microbial carrier, suited to Mediterranean soils where early inoculant establishment is often constrained. Future research should assess the durability of these mechanisms under field conditions to determine their long-term relevance for soil biological functioning and restoration.

Graphical abstract

Keywords

biochar carrier / microbial inoculants / Bacillus velezensis / Trichoderma virens / soil amendment / soil microbial communities

Highlight

	● Biochar derived from olive pomace functions as an efficient microbial carrier.
	● Biochar pores provide protected microsites for bacterial and fungal colonization.
	● Carrier-based inoculation improves early establishment of microbial inoculants.
	● Biochar microhabitats stabilize inoculants with limited community disruption.
	● Olive waste valorization supports sustainable soil biofertilizer strategies.

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