Practices for increasing calcium content and improving fruit quality and shelf life of blueberries

Authors: Bryla, David; Orr, Scott; DEVETTER, LISA - Washington State University; YANG, WEI - Oregon State University

Submitted to: Acta Horticulturae
Publication Type: Proceedings
Publication Acceptance Date: 10/9/2023
Publication Date: 11/16/2023
Citation: Bryla, D.R., Orr, S.T., Devetter, L.W., Yang, W.Q. 2023. Practices for increasing calcium content and improving fruit quality and shelf life of blueberries. Acta Horticulture Proceedings. 1381:309-316. https://doi.org/10.17660/ActaHortic.2023.1381.40.
DOI: https://doi.org/10.17660/ActaHortic.2023.1381.40

Interpretive Summary: Calcium (Ca) contributes to firmness and longer shelf life of fruits and is usually applied to plants by adding gypsum or lime to the soil or by using foliar sprays. However, these materials tend to be ineffective for increasing Ca in berry crops. In cooperation with faculty at Washington State and Oregon State University, an ARS scientist in Corvallis, OR determined whether fertigation, the practice of applying fertilizers through an irrigation system, was an effective means of increasing Ca content and improving fruit quality in blueberry. Fertigation increased Ca in the soil solution but had little effect on the concentration of Ca in the leaves or fruit because applications were limited by low solubility of the fertilizer or to low label rates. Next, we will try fertigating more frequently and using an injector designed specifically for fertigating with relatively insoluble Ca fertilizers.

Technical Abstract: Calcium is a key component of fruit quality and is known to increase berry firmness and shelf life in blueberries. Usually, Ca is applied by adding gypsum or lime to the soil or by using foliar sprays. However, these materials tend to be ineffective for increasing Ca in the fruit. Previously, we determined that nearly all Ca in the fruit is taken up during the short period between the early green and late green stages of berry development. Therefore, maintaining a high concentration of Ca in the root zone during these stages may facilitate uptake of the nutrient into the fruit. One potential way of doing this is to inject Ca fertilizer into the drip irrigation system and apply it by fertigation. Currently, there are a number of Ca products that can be used for fertigation, including micronized solution grade gypsum (which is certified organic) and Ca thiosulfate. We are testing fertigation with both of these products in five cultivars of northern highbush blueberry (Vaccinium corymbosum L.), including ‘Duke’, ‘Earliblue’, ‘Bluecrop’, ‘Elliott’, and ‘Aurora’, and are comparing them to soil applications of gypsum, foliar applications of CaCl2, and control treatments with no Ca fertilizer. So far, we found that fertigation increased Ca in the soil solution relative to the other treatments but had no effect on fruit Ca. In this case, we fertigated once a week from petal fall to fruit colouring using water-driven injectors. Fertigation rates were limited by low solubility of the micronized gypsum and the label rate for calcium thiosulfate. Foliar applications of CaCl2, on the other hand, increased fruit Ca but had negative effects on yield and fruit quality in two of the cultivars. Specifically, it reduced average berry weight by 8% in ‘Bluecrop’ and resulted in 10% more fruit loss from heat damage in ‘Aurora’. Next, we plan to fertigate more frequently (e.g., two or three applications per week) in an effort to increase Ca in the fruit. We will also test a different type of injector for gypsum.