Measuring evapotranspiration of turfgrass

Abstract

Evapotranspiration (ET) of Kentucky bluegrass (Poa pratensis L.) was measured in urban lawns, in a growth chamber and as part of a study relating canopy temperature to water stress. Lysimeters, 30.5 cm in diameter, were used to measure ET. Lack of control over urban lawn sites restricted the reliability of relating ET to microclimate. In the growth chamber study, ET was influenced by day temperature, night temperature, clipping height and soil texture. It was shown that soils high in clay are not desirable for use in lysimeters due to limited root growth. Average midday canopy temperature was more reliable at identifying water stress than daily ET measurements using lysimeters. Canopy temperature measurements, using an infrared thermometer, were utilized without correcting for canopy quality differences since the thermal emissivity of lush, green turf and dead, brown turf was found to be the same. The Barnes 14-220 infrared thermometer was calibrated and its scale was found to be 8% high for the 0-50°C range.