Evaluation of Biochars as Carriers for Rhizobium leguminosarum.

Peat is the standard carrier material used for commercial microbial inoculants produced in Canada and the US. Peat is a slowly-renewable resource and its production is extremely vulnerable to variable weather conditions. Furthermore, it may not be widely available in all countries. We investigated the potential to develop biochar as a carrier material. Our goal was to evaluate if different biochars perform comparably in supporting rhizobial survival, and what characteristics contributed to their ability to support rhizobial survival. Evaluation included characterization of the biochars, assessment of biochar phytotoxicity, survival of Rhizobium on biochars and growth chamber evaluation of two biochars as Rhizobium carriers for inoculating pea. Of the original nine biochars evaluated, six supported Rhizobium leguminosarum for 84 days at 4 C; two supported numbers >1x106 cfu g-1 biochar. The only characteristics that correlated with survival were C:N and % C. The two biochars evaluated delivered R. leguminosarum to pea that initiated nodulation, biomass production and biomass N at levels higher than a non-inoculated control and heat-killed inoculated biochars. We demonstrate that there is considerable potential to develop biochar as a carrier for rhizobial inoculants.