Optimizing Nutrient Management for Organically Grown Blueberries East of the Cascade Range
- Research Status: Project completed 2019 - 2023
Lisa W. DeVetter
Gwen Hoheisel, Joan Davenport, and Gabe LaHue
Northern highbush blueberry (Vaccinium corymbosum) production east of the Cascade Range is an important contributor to the national supply of organic blueberries. However, native soil conditions are alkaline, have high free calcium content, and low in organic matter.
Northern highbush blueberry (Vaccinium corymbosum) production east of the Cascade Range is an important contributor to the national supply of organic blueberries. However, native soil conditions are alkaline, have high free calcium content, and low in organic matter. Although growers amend soils to lower pH and provide organic matter, these soil characteristics influence nutrient cycling and availability.
Growers need data-driven guidelines on how to optimize nutrient management for their unique growing conditions, but few studies have been conducted in this important region. This project addressed that need with an emphasis on organic nitrogen fertility practices by evaluating the effects of commercially available organic nitrogen fertilizer sources applied at low, medium, and high rates on blueberry yield, fruit quality, and various plant and soil variables. Organic fertilizer nitrogen mineralization dynamics were also characterized via a laboratory incubation study at different temperatures. Four different fertilizer sources (blood meal, fish emulsion, WISErganic, and a combination of 40% blood meal and 60% WISErganic) were applied at rates of 50, 100, or 150 lbs N/acre in a randomized complete block split plot design study using ‘Duke’ grown in Prosser, Washington between 2018-2023. Results indicate established ‘Duke’ blueberry is tolerant to a range of organic nitrogen fertilizer sources and rates but is slightly more sensitive to fertilizer rate than source. Based on this long-term study, growers in eastern Washington are advised to avoid high rates of organic fertilizer nitrogen in their mature plantings and rates of 50 lbs N/acre is a good foundation to build a fertilizer program for this unique production region around given it led to no significant yield declines relative to the medium and high rates. Lower fertilizer N rates also minimizes the potential for building up soil EC and potassium to deleterious levels that could threaten crop health and productivity. Throughout the incubation, soils fertilized with fish emulsion, blood meal, and the combination of blood meal plus WISErganic had the highest inorganic nitrogen, with the WISErganic amended soils intermediate between these sources and the unfertilized control soils. The release of nitrogen via mineralization was most rapid in the first 14-28 days and was minimally impacted by incubation temperature, indicating blueberry growers can expect most of the nitrogen in the evaluated fertilizer products to be released relatively rapidly.
Overall, this long-term project provides valuable information that will be incorporated into revised nutrient management guidelines for blueberry in the Pacific Northwest.
Growers need data-driven guidelines on how to optimize nutrient management for their unique growing conditions, but few studies have been conducted in this important region. This project addressed that need with an emphasis on organic nitrogen fertility practices by evaluating the effects of commercially available organic nitrogen fertilizer sources applied at low, medium, and high rates on blueberry yield, fruit quality, and various plant and soil variables. Organic fertilizer nitrogen mineralization dynamics were also characterized via a laboratory incubation study at different temperatures. Four different fertilizer sources (blood meal, fish emulsion, WISErganic, and a combination of 40% blood meal and 60% WISErganic) were applied at rates of 50, 100, or 150 lbs N/acre in a randomized complete block split plot design study using ‘Duke’ grown in Prosser, Washington between 2018-2023. Results indicate established ‘Duke’ blueberry is tolerant to a range of organic nitrogen fertilizer sources and rates but is slightly more sensitive to fertilizer rate than source. Based on this long-term study, growers in eastern Washington are advised to avoid high rates of organic fertilizer nitrogen in their mature plantings and rates of 50 lbs N/acre is a good foundation to build a fertilizer program for this unique production region around given it led to no significant yield declines relative to the medium and high rates. Lower fertilizer N rates also minimizes the potential for building up soil EC and potassium to deleterious levels that could threaten crop health and productivity. Throughout the incubation, soils fertilized with fish emulsion, blood meal, and the combination of blood meal plus WISErganic had the highest inorganic nitrogen, with the WISErganic amended soils intermediate between these sources and the unfertilized control soils. The release of nitrogen via mineralization was most rapid in the first 14-28 days and was minimally impacted by incubation temperature, indicating blueberry growers can expect most of the nitrogen in the evaluated fertilizer products to be released relatively rapidly.
Overall, this long-term project provides valuable information that will be incorporated into revised nutrient management guidelines for blueberry in the Pacific Northwest.
