Abstract:
Accurate estimation of evapotranspiration is important in efficient water management for improving water use
efficiency. In order to obtain evapotranspiration and evaporation beneath the canopy using the Food and Agriculture
Organization (FAO) method, pan evaporation was used instead of reference evapotranspiration calculated by the
Penman-Monteith equation with detailed meteorological data. The total crop coefficient and soil evaporation coefficient were
determined using actual measured daytime evapotranspiration and evaporation by the Bowen ratio energy balance and lysimeter,
respectively, in a rice paddy field in Japan. The average evapotranspiration was 5.3 mm/d, 4.4 mm/d, 7.4 mm/d and 6.3 mm/d
and crop coefficient was 0.79, 1.18, 1.01 and 0.86 for the initial stage, development stage, middle-season stage and late-season
stage, respectively. The evaporation was low and almost constant with an average value around 0.77 mm/d when the leaf area
index (LAI) reached 3. The proposed average crop coefficients for different growing stages were applied to estimate daytime
evapotranspiration and found suitable. A simple soil water evaporation coefficient model was developed using leaf area index
for practical use and it was found that it could accurately estimate evaporation
