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 (H2O2-biochar), biochar treated with nitric acid (HNO3-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 H2O2 treatment significantly boosted its microbial carrier capacity (4.99 × 106 CFU g−1 biochar) as compared to untreated or HNO3-biochar which reached up to 1.03 × 106 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 H2O2-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, H2O2-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 H2O2 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.