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Four different irrigation treatments were compared for three years in this Lapins cherry orchard in The Dalles, Oregon. reserves) and greater postharvest water stress during flower development likely contributed to lower yields observed in 2010. After harvest, cherry tree photosynthe- sis and water use are greatly reduced to nearly half of pre- harvest levels, according to research of Dr. Matthew Whiting, Washington State University. Nonetheless, severe water stress can develop during this period since temperatures are typically highest in the season. We therefore recommend replenishing the soil profile follow- ing harvest. Irrigation timing and cherry water use In our research, irrigations typically began 20 to 45 days after bloom. Measurement of soil moisture in early spring provided a good estimate of the field capacity of the soil, defined as the maximum amount of water a soil can hold after drainage from macropores (Figure 2; 2- and 3-foot depths). Applying irrigation to soils at field capacity is inefficient, noneconomical due to pumping costs, and can augment leaching of highly mobile nutrients such as nitrate from the rooting zone. The amount of water consumed by a tree is directly, and positively, related to the size of its canopy or leaf area. Sweet cherry fruit load is not a strong sink for water. For example, a 5-ton per acre crop of cherries comprises roughly 1,000 gallons of water. For comparison, one irri- gation event per week can deliver between 25,000 to 50,000 gallons of water per acre. In our study, the irriga- tions of Treatment 1 in 2009 and 2010 supplied about one acre-inch per week or 27,150 gallons. Interestingly, cropload level has little effect on a cherry tree's demand for water, since cherry leaves have been shown to photo- synthesize and transpire at similar rates under widely varying fruit loads, reports Whiting. Conclusions Due to adequate soil moisture in early spring through- out most of the Northwest, the short cell division period of cherry fruit that occurs from 10 to 20 days after bloom, and negligible fruit growth during pit hardening, the two critical time periods for managing water to ensure opti- mum production of premium cherries is the month prior to harvest, and postharvest. Allowing depletion of around 50 percent available water during the preharvest interval did not reduce cherry fruit size. However, postharvest irri- gation management should be used to maintain soil water above 50 percent available water. Based on three years of production, irrigating at 55 to 65 percent ET did not significantly reduce yields. If stem water potential is used to schedule irrigations, values should be maintained above -1.4 MPa. Based on the site characteristics in the study, we cannot recommend an irrigation strategy to control shoot growth. Severe stress can develop rapidly on shallow or lightly textured soils, as well as in orchards with dwarfing rootstocks, such as Gisela 5. Under these conditions, increasing the frequency of irrigation to maintain adequate soil moisture and intensive plant and soil monitoring will be critical. • Funding was provided by the Oregon Sweet Cherry Commission and Soil Water Conservation District, with irrigation supplies donated by United Pipe and Supply and soil moisture measurements by Jac leRoux (Irrinet). Omeg Orchards provided the research site. www.goodfruit.com GOOD FRUIT GROWER APRIL 1, 2012 35 courtesy todd einhorn, osu