Daily Evapotranspiration Prediction from Louisiana Flooded Rice Field

Abstract

During 1995, daily evapotranspiration (Et) from a flooded rice field was calculated with a water balance equation using measured values of water level, precipitation, irrigation, seepage, and tailwater runoff. Stagewise Et was 6.3, 8.1, and 6.8 mm/d for the vegetative, flowering, and yield formation stages, respectively; average daily Et was 6.8 mm/d. Grass reference Et (Etr) combination models Penman-Monteith, FAO-Penman, and 1963 Penman were evaluated for their capabilities to predict rice Et using daily weather data. Daily Etr was also calculated by summing up hourly values with the Penman-Monteith method. The Penman-Monteith (daily) method had a coefficient of determination (R2) of 63.7%, as compared with 62.9, 60.0, and 61.7% for Penman-Monteith (hourly), FAO-Penman, and 1963 Penman methods, respectively. Crop coefficients (Kc) using the Penman-Monteith (daily) model were 1.39, 1.51, and 1.43 for the vegetative, flowering, and yield formation stages, respectively. Developed Kc values were verified using limited rice Et data in 1996. The Kc values underpredicted rice Et by 3.7%, which was acceptable for water management.