Estimating turfgrass evapotranspiration using atmometers and the Penman-Monteith model

Information is lacking on the precision of atmometers and empirical models used to estimate turfgrass evapotranspiration (ET). Experiments were conducted to evaluate the precision of black Bellani plates, a class A evaporation pan, and the Penman-Monteith empirical model for estimating ET of 'Mustang' tall fescue (Festuca arundinacea Schreb.), 'Meyer' zoysiagrass (Zoysia japonica Steud.), 'Prairie' buffalograss [Buchloe dactyloides (Nutt.) Engelm.], and 'Midlawn' bermudagrass [Cynodon dactylon (L.) Pers. x transvaalensis Burtt-Davy] under well-watered conditions. Tall fescue was mowed once weekly at 6.5 cm, and warm-season grasses were mowed at 4.5 cm twice weekly. Diurnal ET was measured between June and September in 1993 and 1994 using weighing lysimeters and the water balance method. Evaporation from atmometers was measured during the hour that turfgrass ET was determined, and Penman-Monteith-estimated ET was calculated for the same time period. Black Bellani plate evaporation was correlated most closely with measured turf ET (R(2) = 0.73), followed by class A pan evaporation (R(2) = 0.67), and Penman-Monteith-estimated ET (R(2) = 0.60). Ranking of grasses for mean daily ET was tall fescue (6.8 mm d(-1)) > zoysiagrass (5.6 mm d(-1)) > buffalograss (5.1 mm d(-1)) = bermudagrass (5.0 mm d(-1)). The black Bellani plate provides the most precise estimate of turfgrass ET under well-watered conditions.