INFLUENCE OF VAPOR DEPOSITION ON WILD BLUEBERRY WATER REQUIREMENTS IN A HUMID COASTAL CLIMATE

Growers need recommendations to improve both the timing and amount of irrigation water applied to wild blueberries (Vaccinium angustifolium) in the humid coastal region of Maine where direct vapor deposition may also supply water to the crop. This study was initiated to quantify the rates and timing of vapor deposition in relation to rates of evapotranspiration (ET). Weighing lysimeters were used to determine rates of net water vapor deposition (VD) or vapor uptake (VU) during hours when rainfall and drainage were not occurring. Vapor deposition occurred throughout the evening, night, and early morning during the fruit bearing year of a two year cropping cycle for the period June 11 to October 8, 2003. The mean values of daily VD, VU, and ET were 0.075 cm/d, 0.335 cm/d, and 0.27 cm/d with a coefficient of variability of 71%, 44%, and 71%, respectively. Thus, VD accounted for around 22% of total water taken up by the plants and amounted to 28% of ET. Under these conditions, classical approaches to irrigation scheduling based solely on rainfall measurements may result in over application of water by failing to account for vapor deposition.