LYSIMETER-BASED CROP COEFFICIENTS FOR YOUNG HIGHBUSH BLUEBERRIES

Inexpensive weighing lysimeters ($1475/unit) were constructed for meas uring evapotranspiration of young highbush blueberries (Vaccinium cory mbosum L.). The use of a single load cell and other design characteris tics decreased lysimeter measurement accuracy but minimized lysimeter construction costs. Measurement error was within +/-3%. Crop coefficie nt (CC) curves for 5- and 6-year-old 'Bluecrop' highbush blueberry pla nts in their third and fourth year of production were generated using reference evapotranspiration and crop water use data from the 1991 and 1992 growing seasons, The CC increased during leaf expansion and flow ering in the spring to its maximum value of about 0.19 in 1991 and 0.2 7 in 1992 and remained near these values until leaves began senescing in the fall, Water use on sunny days during June, July, and August ran ged from (liters/bush each day) 3.5 to 4.0 in 1991 and 4.0 to 4.5 in 1 992. During the second year of the study, plants had an average height of 0.9 m, an average diameter of 0.9 m, and covered 18% of the total cultivated area, The maximum calculated CC was equal to 1.5 times the measured canopy cover percentage.