2014 ASHS Annual Conference

Northern highbush blueberry (Vaccinium corymbosum L.) is a long-lived perennial crop (30+ years) well-adapted to acidic soil conditions (pH 4.5−5.5). Plants acquire primarily NH₄- over NO₃-N and tolerate relatively low concentrations of P, K, Ca, and Mg in the soil and high concentrations of plant available metals such as Al and Mn. Leaf and soil nutrient standards are available for blueberry, but the standards are mostly derived from research on one or two cultivars or from anecdotal evidence collected from commercial plantings. Recently, we found that optimal leaf nutrient concentrations may vary in blueberry, depending on the age of the planting, the cultivar, or the method in which the fertilizer is applied. For example, in a new planting, we found that leaf concentrations of many nutrients were within or above the range considered normal for fully-productive mature plants. Plant uptake of most of the nutrients increased throughout the growing season, indicating that it would be best to apply the majority of fertilizers in the spring. However, uptake of K, Mg, Mn, and Zn was greater later in the season, and therefore, it may be better to apply these nutrients, if needed, in early or midsummer. Leaf nutrient concentrations are also higher, in many cases, in early- than in late-season cultivars, or when the plants are fertilized with granular fertilizers than by fertigation in new plantings. We also found that young blueberry plants were sensitive to high soil salinity levels associated with the use of granular N fertilizers and demonstrated that growth and yields were greater when the fertilizer was applied by fertigation. With granular ammonium sulfate, electrical conductivity of the soil solution (ECw) reached levels as high as 13 dS·m^-1 following the first split application in the spring, 10 dS·m^-1 following the second application, and 8 dS·m^-1 following the third application in early summer, which is 5-fold higher, on average, than the level considered safe for blueberry. In comparison, ECw remained <2 dS·m^-1 when the fertilizer was applied weekly from mid April to late July by fertigation. Fertigation is becoming a common practice for highbush blueberry, but much more research is needed to identify the best fertilizer sources of each nutrient to use, determine precisely how much of each nutrient to apply, and to decide exactly when to apply them to a given cultivar.