Subedi, Abhinaya, authorChávez, José L., authorAndales, Allan A., authorColorado State University, publisher2020-02-132020-02-132013https://hdl.handle.net/10217/201033http://dx.doi.org/10.25675/10217/2010332013 annual AGU hydrology days was held at Colorado State University on March 25 - March 27, 2013.Includes bibliographical references.Accurate estimation of crop evapotranspiration (ET) is important to know how much water is required during the growing season, to improve crop water management, to conserve soil and water resources and for water rights purposes. Various forms of semi-empirical equations have been developed to estimate crop ET. The ASCE-EWRI Standardized Penman-Monteith (PM) equation and the full version of the Penman-Monteith equation have been used in this study to estimate alfalfa ET. The ASCE-EWRI Standardized PM equation along with crop coefficients (Kc) can be used to estimate actual crop ET. The full version of the PM equation can be applied to calculate actual ET directly for unstressed crop conditions using weather and crop variables. In this study, both PM ET methods were evaluated using a monolithic precision weighing lysimeter. The research was carried out at the Colorado State University- Arkansas Valley Research Center, Rocky Ford, Colorado. Data from 2009 and 2010 from a large precision monolithic weighing lysimeter were used. The performance evaluation of the PM equations was done for different atmospheric stability conditions. The statistical analysis included the mean absolute error, mean biased error, root mean squared error, linear regression slope-intercept (and goodness of fit), and the index of agreement. The evaluation was done using days where the alfalfa was at reference conditions. The results showed that both PM ET methods compared satisfactorily with the lysimeter ET values, however, both methods underestimated actual alfalfa ET. It was also observed that the bias was larger in unstable than in stable atmospheric condition for both methods.born digitalproceedings (reports)engCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.Text