Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2007
Publication Date: 3/1/2007
Citation: Bryla, D.R., Strik, B.E. 2007. Effects of cultivar and plant spacing on the seasonal water requirements of the highbush blueberry. Journal of the American Society for Horticultural Science. 132:270-277.
Interpretive Summary: Many growers in the Pacific Northwest are planting blueberry fields at higher densities to improve yields and increase the number of berries harvested per acre in the first few years after planting. The objective of this study was to determine the effect of high-density planting on highbush blueberry water requirements. Although close spacing reduces individual plant size, we expected that plants spaced closer together would require more irrigation per unit land area than those spaced further apart due to increased canopy coverage within rows. The study utilized a 5 year-old planting of highbush blueberry, consisting of three cultivars, 'Duke', 'Bluecrop', and 'Elliott', planted 1.5 (0.45 m) and 4.0 (1.2 m) ft apart within rows. Surprisingly, plants spaced 1.5 ft apart required only slightly more water than those spaced 4.0 ft apart. Close spacing also increased yield per acre and crop water use efficiency. Plants spaced 1.5 ft, however, required more frequent irrigations due to their smaller root systems, especially during fruit filling. A denser canopy at 1.5 ft also reduced water penetration to the roots during irrigation by overhead sprinklers. Water use by each cultivar increased during fruit filling and then rapidly decreased after harvest. 'Duke' required the most water among cultivars, using 0.20-0.39 in/day (5-10 mm/day) from mid-May to mid-August, while 'Elliott' required the least, using 0.12-0.20 in/day (3-5 mm/day).
Technical Abstract: Effects of planting density on irrigation requirements and water use efficiency were investigated in 'Duke', 'Bluecrop', and 'Elliott' northern highbush blueberries (Vaccinium corymbosum L.) spaced 0.45 or 1.2 m apart within rows and 3.0 m apart between rows in October 1999. Plants were irrigated by overhead sprinklers and data was collected at 4 and 5 years after planting. Fruit were harvested late June to early July in 'Duke', early to mid July in 'Bluecrop', and mid July to mid August in 'Elliott'. Each cultivar was shallow rooted and sensitive to water stress; most roots were located <0.4 m deep and plant water potential declined within 5-7 days without rain or irrigation. Plants were smaller when spaced at 0.45 m, but canopy coverage, total dry weight, and water use per ha were higher. Close spacing also increased crop yield and water use efficiency (i.e., kg of fruit produced per cubic meter of water acquired). Water requirements were highest during fruit development, but declined sharply after harvest, especially in Duke, which among cultivars, used the most water at 5-10 mm/day. 'Elliott' used the least at only 3-5 mm/day. Lower water use in 'Elliott' may have been related to a later and extended fruit ripening period, lower plant water status due to its larger canopy size, and lower penetration of water into the root zone during overhead irrigation. Thus, longer irrigation sets or alternative irrigation methods, such as drip, may be required when growing dense canopy cultivars at closer in-row spacings.