Nitrogen Fertilizer Practices for Rapid Establishment of Highbush Blueberry: a Review of Six Years of Research

Three field trials were conducted in Oregon, USA, from 2006 to 2011 to evaluate nitrogen (N) fertilizer practices for establishment of highbush blueberry (Vaccinium corymbosum L.). In the first trial, planted in April 2006, we compared the effects of N fertigation (injection of fertilizer through a drip system) to conventional granular fertilizer application in 'Bluecrop' blueberry and found that fertigation produced more growth and less salt injury in young plants than granular fertilizers, but fertigation required >= 150 kg . ha(-1) N to reach maximum plant growth potential during the first 2 years after planting. More N was needed by fertigation because NH4-N, the preferred form of N by blueberry, is immobile in soil. Unlike granular fertilizer, which was applied by hand around the base of the plants, much of the injected fertilizer wound up between the young plants and therefore was unavailable for plant uptake. In the second trial, planted in October 2008, we examined the effects of fertigation using three different methods of water placement in six cultivars of blueberry, including 'Earliblue', 'Duke', 'Bluecrop', 'Draper', 'Elliott', and 'Aurora', and found that two laterals of drip, which is now a common practice in blueberry, was worse in each cultivar than a single line. Drip emitters with two lines placed the NH4-N fertilizer too far from the roots of the young plants and resulted in low leaf tissue N levels. The third and most recent trial was planted with 'Draper' in October 2010. The objective of this study was to identify fertilizer practices that increase N uptake and plant productivity during establishment, including humic acids, controlled-release fertilizers, and small but safe application of granular fertilizer shortly after planting. We hypothesized that any fertilizer method that increases availability of soil N in the root zone during establishment will also likely improve early growth and production. After 1 year, we found once again that drip placement was important, where fertigation with one or two laterals located near the base of the plants produced more growth than two laterals located 0.2 m from each side of the plants, even when granular or slow-release fertilizer was applied in early spring prior to fertigation. Fertigation with humic acid fertilizer or urea sulfuric acid also produced better growth than liquid urea commonly used in blueberry. Work is underway to further evaluate the response of blueberry to different forms NH4-N fertilizer.