Biochar As a Carrier Substrate for Microbial Inoculants.

Many bacteria and fungi are added to agricultural soils purposefully to enrich soil populations of organisms that perform desirable functions, such as the nitrogen-fixing root nodule bacteria, rhizobia. Inoculant organisms are supported in a carrier material to keep them stable and present in high numbers until they can be used in the field. For rhizobia, the preferred carrier substrate is finely ground peat, although vermiculite and bagasse, among other stable carbon substrates including charcoal, have been used successfully. We evaluated the use of biochar as a carrier substrate for Rhizobium phaseoli and Bradyrhizobium japonicum. A range of biochars, varying in biomass source (feedstock) and temperature of pyrolysis, were compared to the peat standard by assessing their respective abilities to support high numbers of these rhizobia over time when held at 30C. Selected biochar inoculants were examined by electron microscopy to visualize the cell –biochar interface and evaluate colonization patterns and biochar coverage. Biochar colonization was also examined using the Bac-light approach to distinguish live from dead cells over months of incubation. Biochar has high promise as an alternative, readily available substrate for rhizobia bacteria inoculants. Evaluation of biochar as a carrier substrate for Trichoderma, arbuscular mycorrhizae and phosphate solubilizing bacteria are in the pipeline.