Submitted to: World Congress of Soil Science
Publication Type: Proceedings
Publication Acceptance Date: 2/15/2010
Publication Date: 8/6/2010
Citation: Lascano, R.J., Evett, S.R. 2010. Calculation of canopy resistance with a recursive evapotranspiration model[abstract]. World Congress of Soil Science. August 1-6, 2010, Brisbane, Australia. p. 20-23.
Technical Abstract: The calculation of hourly and daily crop evapotranspiration (ETc) from weather variables requires a corresponding hourly or daily value of canopy resistance (rc). An iterative method first proposed by MI Budyko to calculate ETc finds the surface canopy temperature (Ts) that satisfies the crop’s energy balance. This method was used to calculate both hourly and daily values of rc over a well-watered and established alfalfa crop for 26 days during the 1999-growing season in Bushland Texas. Hourly values of rc were obtained using a graphical procedure from first, values of ETc measured with a large weighing lysimeter; and second, from values of Ts measured with a radiometer. Results show that the daily seasonal average alfalfa rc was 45 ± 12 s/m for both methods of calculating rc. In the absence of a lysimeter installation to measure hourly ETc the measurement of Ts with a radiometer provides an alternative and practical means to calculate rc provided that other required weather input variables are also measured over the crop canopy.