Nutrient requirements, leaf tissue standards, and new options for fertigation of northern highbush blueberry

Authors: Bryla, David; STRIK, BERNADINE - Oregon State University

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2015
Publication Date: 9/1/2015
Citation: Bryla, D.R., Strik, B.C. 2015. Nutrient requirements, leaf tissue standards, and new options for fertigation of northern highbush blueberry. HortTechnology. 25(4):464-470.

Interpretive Summary: Northern highbush blueberry is well adapted to acidic soils with low nutrient availability but often requires regular applications of nitrogen (N) and other nutrients for profitable production. Typically, nutrients accumulate in the plant tissues following the same pattern as dry matter and are lost or removed by leaf senescence, pruning, fruit harvest, and root turnover. Leaf tissue testing is a useful tool for monitoring nutrient requirements in northern highbush blueberry, and standards for analysis have been updated for Oregon. Until recently, most commercial plantings of blueberry were fertilized using granular fertilizers. However, many new fields are irrigated by drip and fertigated using liquid fertilizers. Suitable sources of liquid N fertilizer for blueberry include ammonium sulfate, ammonium thiosulfate, ammonium phosphate, urea, and urea sulfuric acid. A number of growers are also applying humic acids to help improve root growth and are injecting sulfuric acid to reduce carbonates and bicarbonates in the irrigation water. Although only a single line of drip tubing is needed for adequate irrigation of northern highbush blueberry, two lines are often used to encourage a larger root system. The lines are often installed near the base of the plants initially and then repositioned 6–12 inches away once the root system develops. For better efficiency, N should be applied frequently by fertigation (e.g., weekly), beginning at bud break, but discontinued at least 2 months prior to the end of the growing season. Applying N in late summer reduces flower bud development in northern highbush blueberry and may lead to late flushes of shoot growth vulnerable to freeze damage. The recommended N rates are higher for fertigation than for granular fertilizers during the first 2 years after planting but are similar to granular rates in the following years. More work is needed to develop fertigation programs for other nutrients and soil supplements in northern highbush blueberry.

Technical Abstract: The differences between fertigation and granular fertilizer were compared using different sources of N fertilizer during the first 5 years of fruit production in northern highbush blueberry (Vaccinium corymbosum). Soil pH was slightly lower with granular fertilizers than with fertigation. However, leaf N was also lower with granular fertilizer, while yield was greatest when plants were fertigated using ammonium sulfate or urea sulfuric acid. The results indicated that northern highbush blueberry is well suited to fertigation. Higher rates of N fertilizer likewise increased plant growth but did not improve yield in any year and reduced berry size during the first few years of fruit production. Whether N was applied by fertigation or as granular fertilizer, only 67-93 kg/ha of N or less was needed per year to optimize fruit production. On most soil types, only one line of drip tubing per row is needed for adequate irrigation, but two lines per row is often used to encourage a larger root system and increase plant access to soil nutrients. The lines are often located near the base of the plants during the first year or two after planting and later repositioned 15-30 cm on each side of the plants as the root system develops. Liquid fertilizers should be injected in small and frequent applications (e.g., once per week), starting at leaf emergence and finishing in late July or early August. Fertigation is not recommended for the entire growing season (e.g., April–September) because N applications in late summer reduce flower bud development in northern highbush blueberry and may lead to late flushes of growth that increase the potential for freeze damage over the winter. Avenues for future research on nutrient management in blueberry include fertigation with other nutrients besides N and more work on soil supplements such as humic and fulvic acids.