Chemically and biologically activated biochars as potential inoculant carriers, biofertilizers or plant disease suppressors

Abstract Background The interaction of biochar with beneficial microorganisms and its role as a plant disease suppressor has garnered significant research interest, yet these roles in activated or oxidized biochars remain insufficiently explored. This study investigated three activated biochars derived from the same wood-based biochar: biochar treated with hydrogen peroxide (H 2 O 2 -biochar), biochar treated with nitric acid (HNO 3 -biochar), and biochar treated with elemental sulfur and chitin (biochar + S + chitin), produced by incubating the raw biochar with elemental S and chitin. To evaluate the fungal carrier capacity, activated biochars were inoculated with a plant-beneficial fungus ( Trichoderma asperellum ), and population growth was measured using colony-forming unit (CFU) counts. Plant disease suppressive capacity was assessed by measuring leaf area and root development in cress plants inoculated with the plant pathogen Globisporangium ultimum. Results First, the inoculation of activated biochars with T. asperellum showed that the H 2 O 2 treatment significantly boosted its microbial carrier capacity (4.99 × 10 6 CFU g −1 biochar) as compared to untreated or HNO 3 -biochar which reached up to 1.03 × 10 6 CFU g −1 biochar. Second, we studied the application of chitin, an organic fertilizer, to activate the biochar biologically and increase its N content. The addition of chitin to biochar increased the microbial activity when using H 2 O 2 -biochar or combining biochar with S, as observed by the increase in either sulfate, nitrate, or electrical conductivity. When added to the growing media for cress cultivation, H 2 O 2 -biochar incubated with chitin demonstrated disease suppression against G. ultimum . Chitin also notably increased the mineral N concentration of biochar’s blend, particularly when combined with S, with concentrations reaching 835 mg mineral N L −1 biochar after 12 weeks of incubation. Conclusions Activated biochar with H 2 O 2 demonstrated effective plant growth-promoting fungi carrier capacity. The combination of elemental S and chitin not only enhanced the suppressive potential of biochar, but also showed promise for the development of biochar-based N fertilizers. Graphical abstract