Influence of Coastal Proximity on Evapotranspiration Rates and Crop Coefficients of Maine Lowbush Blueberry (Vaccinium angustifolium).

Supplemental irrigation can be a viable means of increasing lowbush blueberry (Vaccinium angustifolium) crop yields in humid environments. To best utilize this management technique, Maine growers require accurate knowledge of regional crop water demands. Meteorological data and weighing lysimeters were used to determine Penman-Montieth grass reference evapotranspiration (ETo) rates and actual evapotranspiration rates of the lowbush blueberry at five irrigated and two nonirrigated fields of varying distance from the Maine coast. Mean daily values of air temperature, relative humidity range, and solar flux were all found to increase with increasing distance from the coast. The frequency of growing season fog hours increased from 3.7% of all hours at a distance of 22.5 km from the coast, to 11.1% of all hours at a distance of 0.8 km from the coast. Water equivalent inputs from fog per growing season at these two sites averaged 7.2 cm and 18.3 cm, respectively. These geographic climatic differences were reflected in the calculated evapotranspirationo rates, which also generally increased with distance from the coast. Four-year mean weekly ETo rates for July, the month of greatest potential water demand, were 2.76 cm/week, 3.21 cm/week, 3.52 cm/week, and 4.23 cm/week for sites located 0.8 km, 6.4 km, 22.5 km, and 48 km, respectively, from the coast. Actual ET rates for both crop and prune rotations followed a similar pattern of increasing magnitude with distance from the coast. For July, mean crop and prune year pooled weekly ET rates at 0.8 km, 6.4 km, and 22.5 km from the coast were: 1.69 cm/week (0.85), 2.28 cm/week (0.73), and 2.40 cm/week (0.83), respectively. Standard condition crop coefficient (Kc) values for both rotations during the months of May through September were calculated to be 0.68 for sites 6.4 and 22.5 km from the coast. Thus, it would appear that the same Kc value can be used universally within the typical growing range of the Maine lowbush blueberry. These findings should substantially contribute to improved water use efficiency for the irrigated lowbush blueberry in Maine. [ABSTRACT FROM AUTHOR]