Biochar as an alternative soil amendment for establishment of northern highbush blueberry

Authors: SALES, BRYAN - University Of North Carolina; Bryla, David; Trippe, Kristin; Scagel, Carolyn; STRIK, BERNADINE - Oregon State University; SULLIVAN, DAN - Oregon State University

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2021
Publication Date: 1/17/2022
Citation: Sales, B.K., Bryla, D.R., Trippe, K.M., Scagel, C.F., Strik, B.C., Sullivan, D.M. 2022. Biochar as an alternative soil amendment for establishment of northern highbush blueberry. HortScience. 57(2):277-285. https://doi.org/10.21273/HORTSCI16257-21.
DOI: https://doi.org/10.21273/HORTSCI16257-21

Interpretive Summary: Blueberry is adapted to well-drained soils with low pH and high organic matter. To increase organic matter, growers often incorporate bark or sawdust into the soil prior to planting blueberry and use them as mulch afterwards; however, the cost of these materials is increasing and availability is limited in many regions. Recently, we conducted a set of preliminary trials in a greenhouse to determine whether biochar could be used as an alternative amendment for highbush blueberry. Within 12 weeks, the plants grown in soil with the biochar were larger and more heavily colonized by beneficial soil fungi, called mycorrhizae, than those grown in unamended soil. Additional growth and colonization was achieved under nitrogen-limited conditions by adding bokashi (a mix of fermented wheat bran, molasses, and naturally occurring microbes) to the biochar. The objective of the present study was to determine whether biochar could improve growth and early fruit production of highbush blueberry under field conditions. Biochar, alone or in combination with bokashi or sawdust, was incorporated in the planting hole or row and compared to unamended soil and the conventional practice of incorporating sawdust in the row. Plant response as well as amendment costs were considered to identify the best practices for using biochar in blueberry. Based on the results of this study, biochar appears to have considerable potential for improving growth and fruit production in new plantings of highbush blueberry. The most cost-effective method to apply biochar was adding it to the planting hole. Doing so was much more economical than applying it to the row and cost $535 per acre less than the industry standard of incorporating sawdust in the row. These findings indicate that biochar is a promising soil amendment for commercial production of highbush blueberry.

Technical Abstract: Biochar, as a soil amendment, has been reported to improve plant growth by increasing soil moisture and retaining nutrients. In a previous 12-week greenhouse study, we found that amending soil with biochar alone or in combination with bokashi (fermented wheat bran) increased plant growth relative to unamended soil in highbush blueberry (Vaccinium sp.). The biochar was produced by gasification (700–800 C) of douglas fir [Pseudotsuga menziesii (Mirb.) Franco] bark, wood chips, and wood fiber (referred to as “hog fuel”). In the current study, we aimed to confirm those findings under field conditions in western Oregon. The specific objectives of this 2-year study were to determine the effect of amending soil with biochar or a combination of biochar and bokashi on growth and early fruit production during establishment of highbush blueberry. To achieve these objectives, we transplanted ‘Duke’ northern highbush blueberry (V. corymbosum L.) into soil that was unamended or amended with biochar, 4 biochar : 1 bokashi (by volume), or 4 biochar : 1 douglas fir sawdust (by volume). Each amendment was either applied in the planting hole or incorporated into the row. A treatment with douglas fir sawdust incorporated into the row was also included and represented the industry standard for the region. Plants grown in soil amended with biochar (in the planting hole or row) had 40% to 74% greater total dry weight at the end of the first growing season and 70% to 82% greater fruit yield in the second season than those grown with no amendments or in soil with sawdust. However, leaf Mg concentrations were lower with biochar, suggesting it could limit Mg uptake in blueberry. Soil amended with sawdust, on the other hand, was higher in organic matter, microbial activity, and wet stable aggregates than the other soil treatments but resulted in lower leaf N concentrations during the second year after planting. Unlike in the greenhouse, there was no benefit to using biochar with bokashi. Adding 4 L of biochar to the planting hole was considerably more economical than applying it to the row and cost $1320/ha less than the industry standard of incorporating sawdust in the row. These findings indicate that biochar is a promising soil amendment for commercial production of highbush blueberry.