Beneficial use of biostimulants in Northern highbush blueberry

Authors: Bryla, David; VARGAS, OSCAR - Dole Chile Sa

Submitted to: Acta Horticulturae
Publication Type: Proceedings
Publication Acceptance Date: 7/26/2022
Publication Date: 3/1/2023
Citation: Bryla, D.R., Vargas, O.L. 2023. Beneficial use of biostimulants in Northern highbush blueberry. Acta Horticulturae. 1357:44-50. https://doi.org/10.17660/ActaHortic.2023.1357.7.
DOI: https://doi.org/10.17660/ActaHortic.2023.1357.7

Interpretive Summary: Biostimulants are a rapidly expanding sector within agriculture. They are typically used as soil supplements in agriculture and include various products such as organic acids. Previously, we found that organic acids increased growth of blueberries during the first year after planting and improved root production by at least 50% by the following year. Since then, many growers have started using these products. In this study, we confirmed that organic acids are beneficial to blueberry, particularly during establishment, but we still have questions on whether they are useful in healthy, mature plantings. Growers are also starting to use other types of biostimulants such as seaweed extract and bacterial amendments. Here, we found preliminary evidence that seaweed extract may also provide a benefit to blueberry; however, we found no benefit to amending the soil with commercially available strains of nitrogen-fixing bacteria. Recently, we initiated new studies to examine the response of blueberry to different rates of organic acids in various cultivars and soil types. Once completed, the results will help growers improve production in blueberry and enhance fruit quality for consumers.

Technical Abstract: Many growers are using biostimulants such as humic substances and natural extracts from seaweed in an effort to improve plant growth and production in their crops. These products are typically used as foliars or soil supplements and often work best when applied with fertilizers. Initially, we discovered that application of humic substances (humic and fulvic acids) increased plant growth during the first 2 years after planting in ‘Draper’ northern highbush blueberry (Vaccinium corymbosum L.). The effects of the humic substances on root growth were particularly apparent and resulted in 49-52% more dry root biomass than either conventional fertigation or a control treatment that lacked humic substances but contained exactly the same nutrients as the treatment with humic substances. We then conducted a trial in a mature planting of ‘Bluecrop’ northern highbush blueberry. In this case, humic substances increased root growth and the availability of P and Zn in the soil relative to controls with fertilizer only, but after 3 years, they had no effect on shoot growth, yield, or fruit quality. Next, we tested several different biotimulants, including humic substances, extracts from Ascophyllum seaweed, and a mix of N-fixing bacteria (Azorhizobium caulinodans, Azoarcus indigens, and Azospirillium brasiliense), on potted plants of ‘Draper’ blueberry. Fertigating with humic substances or seaweed extract increased growth of the plants relative to using the bacterial mix or nutrients only; however, the response was quite different between the two products. Plants grown with humic substances were greener and contained more N than those in the other treatments, while those grown with seaweed extract tended to be taller and more upright. Clearly, the use of these products can be beneficial during establishment of highbush blueberry, but more research is needed to determine exactly how they work and whether they are useful under all circumstances.