Evapotranspiration of irrigated alfalfa in a semi-arid environment
1998
We tested Penman-Monteith (PM) and Kimberly Penman (1982) equation predictions of reference evapotranspiration (ETR) against alfalfa (Medicago sativa, var. Pioneer 5454) ET measured to 0.05 mm precision with weighing lysimeters under reference conditions in 1996-97 on Pullman clay loam (Torrertic Paleustoll) at Bushland, TX. Yield from 4 cuttings was 16.5 dry t/ha in 1996, and 16.4 t/ha in 1997. Crop water use averaged 1.01 m per year. Daily alfalfa ETR predicted using PM methods and half-hourly weather data compared well with our measurements (regression r2 of 0.95, SE of 0.6 mm, and slope of 0.97). Use of daily weather data increased SE to 0.8 mm (r2 of 0.90, slope of 0.99) and introduced a positive offset of 0.5 mm. The Kimberly Penman (1982) equation used with daily weather data produced biased predictions (r2 of 0.91, SE of 0.7 mm, intercept of 0.8 mm, and slope of 0.88).
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