Activating biochar by manipulating the bacterial and fungal microbiome through pre‐conditioning

Biochar can enhance plant growth and reduce diseases, but frequently the optimal doses for these two benefits do not coincide. An approach is needed that will extend the range of biochar doses resulting in a concurrence of maximum benefits for both plant productivity and disease suppression. A biochar-amended growth medium was pre-conditioned by pre-planting fertigation in order to enhance the indigenous microbial community structure and activity. Cucumber plant performance and resistance against damping-off caused by Pythium aphanidermatum were monitored. Soil microbial activity, as well as bacterial and fungal community structure, were assessed by high-throughput 16S rRNA and ITS1 gene amplicon sequencing. Pre-conditioning enhanced the efficacy of biochar for improving plant performance and suppressing soilborne disease through enriching the medium in beneficial soil microorganisms, increasing microbial and fungal diversity and activity, and eliminating biochar phytotoxic compounds. The pre-conditioning process brought dose-response curves for both growth and disease resistance into sync, resulting in maximum benefits for both. These findings suggest that pre-conditioning should be incorporated as an important stage during biochar application in soil and soilless media.