2018 ASHS Annual Conference

Biochar has been shown to improve soil conditions such as cation exchange capacity, porosity, pH, and beneficial microbial activity, and to suppress infection by soil-borne pathogens, but it has received relatively little attention in the horticulture industry. Two experiments were conducted in a greenhouse to determine the potential of using biochar as a soil amendment for northern highbush blueberry (Vaccinium corymbosum L. ‘Legacy’). In Expt. 1, plants were fertilized once per week with a complete fertilizer solution (30–10–10) and irrigated twice per week. In Expt. 2, plants were fertilized once per month with 600 ppm of ammonium sulfate and irrigated three times per week. In both cases, the plants were grown in 4-L pots filled with soil (sandy clay) only or with soil amended with biochar or a biochar/bokashi blend at rates of 10% or 20% by volume. Half of the plants in each soil treatment were then inoculated with Phytophthora cinnamomi, which causes root rot. In the absence of P. cinnamomi, plants amended with 20% biochar or 10% or 20% biochar/bokashi blend had greater leaf area and 30% to 70% more total dry weight than those amended with 10% biochar or soil only. The biochar amendments also increased soil aggregation and root colonization by ericoid mycorrhizal fungi. The percentage of roots colonized by mycorrhizal fungi was ≤ 10% in soil only and ranged from 54% to 94% with the amendments. Plants inoculated with P. cinnamomi were stunted and showed typical symptoms of root rot. Root infection by the pathogen negated any growth benefits of biochar or biochar/bokashi and was greater in plants grown with the amendments than in those grown without them. Overall, amending soil with biochar appears to be a promising means of promoting plant growth and mycorrhizal colonization in northern highbush blueberry, but it may not suppress phytophthora root rot.