Few studies are available on evapotranspiration and crop-water relationships of rice in the tropical dry season. We measured evapotranspiration, leaf water potential, stomatal resistance and attendant micrometeorological parameters in an irrigated rice crop during the 1979 dry season. A wind barrier of 50% porosity was used to vary primary meteorological parameters. Diurnal changes in crop water status provided a characterization of the dynamic nature of evapotranspiration, water potential in the crop and stomatal behavior. Modification of vapor pressure deficit (saturation deficit) and wind speed over the canopy by the wind barrier resulted in a 20% decrease in daily evapotranspiration.
Estimations of actual evapotranspiration (Ec) rates based on micrometeorological measurements and a generalized combination formula agreed well with measured evapotranspiration (ET). The concurrence of Ec with ET values and their relation to potential evapotranspiration (E0) indicate a significant crop resistance in these tropical dry season conditions, i.e., Ec (ET)=0.82E0. A significant downward heat flux illustrated the importance of sensible heat in this season. Measurements on five dates throughout the crop season showed that ET is approximately 1.5 times equivalent net radiation.