A Radiometric Surface Temperature Approach To Measure Turfgrass Evapotranspiration.

Accurate measurement of turfgrass evapotranspiration (ET) is valuable for efficient irrigation management and turfgrass germplasm screening for drought response. Inaccurate estimates lead to inefficient water use and poor turfgrass quality which diminishes the multitude of benefits that healthy turfgrass offers. Many methods exist to measure actual or estimated ET, but each with its primary purpose and many with undesirable attributes. This variability makes ET comparison between methods difficult and ultimately turfgrass selection for various water management situations challenging. The objective of this study is to validate the use of a radiometric surface temperature approach to measure turfgrass ET. The remote sensing approach was validated by comparing it to the Bowen ratio, while also demonstrating the use of the lysimeter and FAO-56 Penman-Monteith methods. Evapotranspiration was predominantly measured from for the seven hour primary ET period during the day on more than 50 days in 2012 and 2013 over 6 cm Kentucky bluegrass turfgrass on a silt loam soil in Madison, WI. Penman-Monteith estimates exceeded Bowen ratio measurements, demonstrating the need for crop coefficients. There was variation within lysimeter measurements, making it difficult to determine the accuracy and actual ET value. Some radiometric approaches over estimate sensible heat fluxes from sensors picking up energy associated with the non-transpiring vegetated thatch layer associated with turfgrass. However, the evapotranspiration mapping algorithm radiometric surface temperature approach approximated ET well compared to the Bowen ratio. A radiometric surface temperature approach is an accurate way to measure actual turfgrass evapotranspiration while being far less intrusive to the soil an canopy and less intensive than lysimeter methods.