Energy Balance and Water Use of Rice Grown in the Central Valley of California
1971
Lourence, F. J. | Pruitt, W. O.
Very little basic work has been done within the USA on the energy balance of a rice crop (Oryza sativa L.) as affected by surface and climatic conditions. During 1968 and 1969, energy-balance studies were conducted in the middle of a very large rice field 40.2 km (25 mi) north of Davis, California. Evapotranspiration data obtained were compared with data from a large weighing lysimeter at Davis, planted to grass. From daily ratios thus obtained, estimates of normal monthly evapotranspiration for rice were obtained, using data from the long-term lysimeter study at Davis. For a May 1 to October 1 period, a not~nal seasonal use for rice of 920 mm (36.2 in) was indicated, a value only 3.5% greater than the 10-year mean of 889 mm of water used by rescue (Festuca eliator L.) at Davis during the same period. Air temperature differences between the rice site and the Davis lysimeter were rather minor, but humidities were markedly higher over the rice. Lower wind speed at the rice site, no doubt, contributed to the higher hmnidity, although the very extensive up-wind fetch of rice (2 km or greater) was probably a more important factor. The much higher humidities and somewhat lower wind speeds at the rice site are believed to have reduced the evaporation potential by as much as 20 to 25% below that at Davis. Although in this study evapotranspiration by rice and by grass was very similar, it is estimated that losses by rice, in a plot similar in size to the grass plot, would have exceeded the loss by grass by as much as 20 to 25% if the two crops had been grown at Davis.
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