Fertigation with nitrogen and other nutrients in northern highbush blueberry

Abstract

Most highbush blueberry (Vaccinium sp.) fields are irrigated by drip. A major advantage of drip is the ability to fertigate and apply fertilizers directly through the irrigation water. A series of studies were conducted in western Oregon, USA to identify the best practices for applying N and other nutrients by fertigation. Fertigation with various fluid NH4-N sources, including ammonium sulfate, urea, and urea sulfuric acid, produced more growth and greater yield than conventional granular fertilizers in ‘Bluecrop’ blueberry. Furthermore, applying humic substances in combination with N fertigation nearly doubled root production during the first 2 years after planting. To apply other nutrients, soluble potassium sulfate and potassium thiosulfate are good sources for fertigation in blueberry. Both fertilizers had an immediate effect on availability of K and other nutrients in the soil solution and after 2 years increased the nutrient status of ‘Duke’ blueberry. However, whether applied by fertigation or as a granular product, there was no benefit to fruit production at sites with sufficient soil K. Phosphorus fertilizers also had no effect on mineral nutrition or fruit production, even under P-limited conditions, in ‘Duke’ or ‘Bluecrop’. In this case, the soil was high in clay and likely bound much of the P. The use of B fertilizers, on the other hand, increased the concentration of B in the leaves and fruit of ‘Earliblue’ and ‘Elliott’ blueberry, particularly when it was applied by fertigation or as a foliar fertilizer. Fertigation with Ca products, including micronized gypsum and calcium thiosulfate, had little effect on Ca in the leaves or fruit of ‘Duke’, ‘Earliblue’, ‘Bluecrop’, or ‘Aurora’ but increased fruit firmness of ‘Elliott’ blueberry, particularly in cold storage. Given its potential benefits on fruit quality, we will continue to test fertigation with Ca fertilizers in conventional and organic blueberry fields.