Determination of a crop coefficient for evapotranspiration in a sparse sorghum field

✍ Scribed by Tomomichi Kato; Makio Kamichika

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 141 KB
• Volume: 55
• Category: Article
• ISSN: 1531-0353
• DOI: 10.1002/ird.225

✦ Synopsis

Abstract

The FAO basal crop coefficient K~cb~ and the soil evaporation coefficient K~e~ for a sparse sorghum field in one growing season were estimated using the compartment model (Shuttleworth–Wallace model; S–W model), which separately estimates transpiration from crops and evaporation from the soil. The K~cb~ had a low value of 0.10 (K~cb, ini~) during the initial period, increased rapidly to a maximum of 0.98 (K~cb, mid~) at midseason, and decreased rapidly to 0.53 (K~cb, end~) by the end of the growing season. The K~cb~ increased with increasing leaf area index (LAI) rapidly and slowly, respectively, below and above an LAI of 1.0. The K~e~ showed a positive relationship to increasing soil water content (SWC) at a depth of −15.0 cm, but the soil water content indicated a negative relationship to increasing LAI. Using the dual crop coefficients derived by their relationships to the LAI and soil water content, the actual evapotranspiration (ET~a~) was estimated and compared to the ET~a~ derived by the Bowen ratio energy budget (BREB) method. The root mean square error (RMSE) of the ET~a~ obtained from the simulated crop coefficient to the ET~a~ obtained by the BREB method was 0.84 mm day^−1^. Thus, the adjusted relationship of K~cb~ and K~e~ allowed a good estimation of the evapotranspiration in an irrigated field with sparse vegetation cover. Copyright © 2006 John Wiley & Sons, Ltd.