Estimating Transpiration from Turfgrass Using Stomatal Conductance Values Derived from Infrared Thermometry

Infrared thermometry provides accurate measurements of plant canopy temperature, which, along with basic weather variables, allows estimation of canopy stomatal conductance to water vapor flux (g_c) and transpiration. Our objectives were (i) to compare single- versus two-source energy balance approaches for sensible and latent heat flux calculations; (ii) to use g_c calculated with the method of Blonquist et al. (2009) to estimate transpiration from a dense, well-watered sward of tall fescue (Festuca arundinacea Schreb.) turfgrass; and (iii) to compare calculated canopy transpiration with measured lysimeter evapotranspiration (LYS_ET). The study was conducted from June to October 2012 near Manhattan, KS. Three microlysimeters containing ambient cores of turfgrass were used to measure LYS_ET. Four infrared radiometers, used to measure canopy temperature, were positioned on a weather station that recorded all data necessary for calculating g_c. Transpiration calculated from modeled g_c averaged 1.71 mm d^-1 (29.6%) less than mean LYS_ET, suggesting 29.6% of LYS_ET was from soil water evaporation. Nighttime LYS_ET may have inadvertently contributed to the soil water evaporation component using this method (our conductance model assumed zero nighttime transpiration). Differences were negligible between the single- and two-source energy balance approaches for sensible and latent heat flux calculations. Results indicate transpiration may be reliably estimated via calculation of g_c in turfgrass.