|Hunt, James - UNIVERSITY OF MAINE|
|Starr, Gordon - USDA,NRCS,ENGLEWOOD, OH|
|Yarborough, David - UNIVERSITY OF MAINE|
Submitted to: International Journal of Fruit Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 2, 2008
Publication Date: January 28, 2009
Citation: Hunt, J.F., Honeycutt, C.W., Starr, G.C., Yarborough, D. 2009. Evapotranspiration rates and crop coefficients for lowbush blueberry (vaccinium angustifolium). International Journal of Fruit Science. 8(4):282-298. Interpretive Summary: Yield of blueberry plants is strongly influenced by the availability of water. However blueberry growers need recommendations on how much water to apply and when it should be applied in order to use this water most efficiently. We measured the actual water used by blueberry plants at different field sites in Maine over three years. We compared these measurements with particular meteorological (weather) data and determined that plant water use could be predicted from the meteorological data alone. This will allow blueberry growers to determine when to irrigate and how much water should be applied, thereby more efficiently using and conserving this precious resource for growing the highly popular blueberry crops in Maine.
Technical Abstract: Lowbush blueberry (Vaccinium angustifolium) yield is strongly influenced by water availability; however, growers need more specific irrigation recommendations in order to optimize water use efficiency. Weighing lysimeters were used to determine actual evapotranspiration (ET) rates of lowbush blueberry at one non-irrigated and two irrigated sites within 7 km of the Maine coast. For the 3-year study period, overall mean weekly ET rates (with standard errors) during June, July and August were calculated to be 2.13 (+/-0.05), 2.39 (+/-0.07) and 2.19 (+/-0.07) cm/wk, respectively. Mean crop coefficient (Kc) values were determined from the ratio of daily Penman-Montieth grass reference ET to measured daily ET. The combined mean monthly Kc values for the two irrigated sites varied between 0.61 and 0.74 from May through September, with an overall mean Kc value for all sites of 0.69 (+/-0.02). We found that mean monthly ET rates did not differ significantly between irrigated and non-irrigated sites. Crop Kc values showed no significant rotation-year component. Consequently, the Kc value determined in this study can be used in conjunction with meteorological data to provide Maine lowbush blueberry growers with the ability to better predict water demand by their crop. Fog at the irrigated sites was found to contribute approximately 1.3 cm of net water equivalent per growing season. However, the effects of dew formation and fog deposition are already reflected in the Kc value for each site, enabling growers to determine water demand from these values and grass reference ET data alone. These findings may substantially contribute to improved water use efficiency for irrigated lowbush blueberry in Maine.