Location: Horticultural Crops Research UnitTitle: Potential of deficit irrigation, irrigation cut-offs, and crop thinning to maintain yield and fruit quality with less water in northern highbush blueberry
|ALUMTAIRI, KHALID - Oregon State University|
|STRIK, BERNADINE - Oregon State University|
Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2017
Publication Date: 5/1/2017
Citation: Alumtairi, K., Bryla, D.R., Strik, B.C. 2017. Potential of deficit irrigation, irrigation cut-offs, and crop thinning to maintain yield and fruit quality with less water in northern highbush blueberry. HortScience. 52(4):625-633. doi: 10.21273/HORTSCI11533-16.
Interpretive Summary: Many growers are facing serious water limitations due to warmer and drier weather conditions, increased regulations, and greater demand by other sectors. For example, in 2015, blueberry growers in Oregon and Washington lost an estimated 14 million pounds of fruit due to heat and inadequate water for irrigation. Growers in California are facing even more serious challenges due to a severe on-going drought. If water shortages continue to result in less water for irrigation, the total value of both blueberry production and suitable farmland may be reduced substantially in the region. The objective of the present study was to evaluate the potential of using water-saving management strategies, such as deficit irrigation, irrigation cut-offs, and crop thinning, to maintain yield and fruit quality with less water in northern highbush blueberry. Deficit irrigation is a technique whereby the plants are irrigated with less water than needed during times when yield and quality are uncompromised. Irrigation cutoffs may likewise be effective at reducing water use, provided the cutoffs occur when water demands by the crop are low or less critical to fruit production. Irrigation cut-offs were applied for 4–6 weeks during early or late stages of fruit development. The results indicated that fruit production was unaffected by deficit irrigation and, by the second year, was actually greater with crop thinning than with no thinning in the early cutoff treatment. Late cutoffs, on the other hand, reduced yield but increased several fruit quality characteristics, including firmness, storability, and sugar content of the berries. Compared to using full irrigation, deficit irrigation saved nearly 270,000 gallons/acre of water per year, while early and late irrigation cutoffs saved about 140,000 and 250,000 gallons/acre of water per year, respectively. Implementation of such strategies could result in immediate water savings and would enable growers and irrigation managers to optimize both on-farm and regional water use.
Technical Abstract: Drought and mandatory water restrictions are limiting the availability of irrigation water in many important blueberry growing regions, including Oregon, Washington, and California. New strategies are needed to maintain yield and fruit quality with less water. Three potential options, including deficit irrigation, irrigation cutoffs, and crop thinning were evaluated for 2 years in a mature planting of northern highbush blueberry. Treatments consisted of no thinning and 50% crop removal in combination with one of four irrigation regimes, including full irrigation at 100% of estimated crop evapotranspiration (ETc), deficit irrigation at 50% ETc (applied for the entire growing season), and full irrigation with irrigation cutoffs for 4-6 weeks during early (early to late green fruit stage) or late stages (fruit coloring stage to harvest) of fruit development. Stem water potential was similar with full and deficit irrigation but, regardless of crop thinning, fell by 0.5-0.6 MPa during early irrigation cutoffs and by >2.0 MPa during late cutoffs. In one or both years, fruit ripened fastest with either deficit irrigation or late cutoffs and ripened the slowest with early cutoffs. Yield was not affected by deficit irrigation in plants with a full crop load, but was reduced by an average of 35% with late cutoffs each year and, by the second year, was actually 20% greater with crop thinning than with no thinning in the early cutoff treatment. However, early cutoffs resulted in less soluble solids in the berries than the other irrigation treatments, whereas late cutoffs produced the firmest fruit and the highest soluble solids and acidity in the berries and the slowest rate of fruit loss in cold storage. Based on these results, deficit irrigation and early cutoffs appear to be the most viable options among the treatments tested for maintaining yield with less water in northern highbush blueberry. Relative to full irrigation, deficit irrigation reduced water use by 2.5 ML/ha per year, while early irrigation cutoffs reduced water use by an average of 1 ML/ha per year.