Biochar-based carriers for microbial inoculants in sustainable agriculture: a study on surface properties, microbial viability and persistence

Köves, M. and Szegedi, Á. and Kotroczó, Zs. and Ringer, M. and Madár, V. and Utassy, K. and Kocsis, T. (2025) Biochar-based carriers for microbial inoculants in sustainable agriculture: a study on surface properties, microbial viability and persistence. HUNGARIAN AGRICULTURAL ENGINEERING (44). pp. 57-65. ISSN 0864-7410

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Abstract

Biochar-based carriers have emerged as a potential tool to support microbial inoculants in sustainable agriculture, but their effectiveness depends on the viability and persistence of the inoculated microorganisms. In this study, the viability and persistence of three beneficial microorganisms (Bacillus amyloliquefaciens, Streptomyces griseus, and Trichoderma harzianum) were evaluated on five biochar feedstocks: sunflower husk, wood chips, green waste, pelletized green waste, and a wood–zeolite composite (75:25 ratio). Each biochar was characterized for Brunauer–Emmett–Teller (BET) surface area and pore volume to assess physicochemical properties relevant to microbial habitation. Under sterile conditions, each biochar was inoculated with a single microbial strain and incubated under controlled conditions for ten weeks. Microbial viability was quantified weekly using Most Probable Number (MPN) counts to monitor population dynamics, and a follow-up assay was conducted two months after the initial incubation to evaluate longerterm persistence. The results showed that Bacillus amyloliquefaciens remained viable throughout the ten weeks, and at the follow-up, Trichoderma harzianum similarly persisted across the experimental timeframe, especially on specific biochar types. In contrast, Streptomyces griseus declined rapidly and became undetectable by week seven under the tested conditions. The wood–zeolite composite biochar consistently supported higher survival of the tested microorganisms. In contrast, pelletized green waste exhibited the lowest microbial survival across all strains, despite not having the lowest BET surface area and pore volume. These observations indicate that measuring the biochar surface area alone is insufficient to determine the suitability of carriers for microbial inoculants. Instead, selecting biochar based on a combination of physicochemical properties can improve the design of biochar-based microbial carriers. Overall, these findings support targeted biochar selection to enhance the viability and persistence of beneficial microbes in sustainable agricultural applications.

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