Amending sandy soil with biochar promotes plant growth and root colonization by mycorrhizal fungi in highbush blueberry

Authors: SALES, BRYAN - Oregon State University; Bryla, David; Trippe, Kristin; Weiland, Gerald - Jerry; Scagel, Carolyn; STRIK, BERNADINE - Oregon State University; SULLIVAN, DAN - Oregon State University

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2019
Publication Date: 3/1/2020
Citation: Sales, B.K., Bryla, D.R., Trippe, K.M., Weiland, G.E., Scagel, C.F., Strik, B.C., Sullivan, D.M. 2020. Amending sandy soil with a softwood biochar promotes plant growth and root colonization by mycorrhizal fungi in highbush blueberry. HortScience. 55(3):353-361. https://doi.org/10.21273/HORTSCI14542-19.
DOI: https://doi.org/10.21273/HORTSCI14542-19

Interpretive Summary: There is renewed interest in using biochar as a soil amendment for production of horticultural crops. Biochar is a highly stable, carbon-rich residue produced by pyrolysis, a process by which biomass is thermally decomposed under low oxygen conditions and typically at temperatures less than 700 degrees C. ARS scientists at Corvallis, OR and collaborators at Oregon State University conducted a greenhouse study to evaluate the use of biochar alone or in combination with bokashi (fermented wheat bran) as a soil amendment for blueberry. Benefits under controlled conditions included more plant growth in soil with biochar than in unamended soil and much greater levels of root colonization by beneficial mycorrhizal fungi. Biochar also improved soil aggregation. Addition of bokashi to the biochar improved plant growth and nutrition, particularly under nutrient-limited conditions. Our next step is to test biochar in a new, field planting of blueberry and identify the best method and rate to apply it. Successful practices for using biochar will depend on plant response as well as the cost.

Technical Abstract: Biochar is known to improve soil conditions and to suppress infection by soil-borne pathogens, but its use as a soil amendment has received relatively little attention by the horticulture industry. Two 12-week experiments were conducted in a greenhouse to determine the potential of using biochar as a soil amendment for highbush blueberry (Vaccinium hybrid ‘Legacy’). Plants in the first experiment were fertilized once a week with a complete fertilizer solution and irrigated twice per week, while those the in the second experiment were fertilized once a month with ammonium sulfate and irrigated three times per week. In both cases, the plants were grown in 4-L pots filled with unamended soil (sandy loam) or soil amended at rates of 10% or 20%, by volume, with biochar or a 4:1 mix of biochar and bokashi. Half of the plants in each soil treatment were inoculated with Phytophthora cinnamomi, which causes root rot in blueberry. Although pH of the raw biochar was high (8.5), soil pH averaged 4.5-5.5 in each treatment. In the absence of P. cinnamomi, plants grown with 20% biochar or 10% or 20% biochar-bokashi had greater leaf area and 30% to 70% more total dry weight than those grown with 10% biochar or unamended soil. Biochar also improved soil aggregation and increased root colonization by ericoid mycorrhizal fungi. The percentage of roots colonized by mycorrhizal fungi was 54% to 94% in plants grown with the amendments but was less than or equal to 10% in those grown in unamended soil. Plants inoculated with P. cinnamomi were stunted and showed typical symptoms of root rot. Root infection by the pathogen was unaffected by biochar or biochar-bokashi and negated any growth benefits of the amendments. Overall, amending soil with biochar appears to be a promising means of promoting plant growth and mycorrhizal colonization in blueberry, but it may not suppress phytophthora root rot.