Energy Balance and Water Use of Rice Grown in the Central Valley of California¹

Abstract

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 normal 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 fescue (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 humidity, 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.

A simple evapotranspiration model of a paddy field in tropical Asia

“…These two estimates would give crop coefficient or pan factor (defined as ratio of crop field's evapotranspiration to class A pan evaporation) of 0.93 and 0.76 with a mean value of 0.85. These values are very close to what has been reported for rice (LOURENCE and PRuITT, 1971;CHAPMAN and KININMONTH, 1972;WICKHAM and SEN, 1978).…”

Water balances and evapotranspiration in water- and dry-seeded rice systems

“…3). A number of studies evaluating ET in rice systems show increasing K c values as the crop progresses through flowering and then decreasing (Tomar and O'Toole 1980;Lourence and Pruitt 1971;Alberto et al 2011;Shah and Edling 2000)-a trend that is not immediately apparent in this study.…”

Seasonal Losses of Dissolved Organic Carbon and Total Dissolved Solids from Rice Production Systems in Northern California

“…Water management affected whether rice productions systems were net importers or exporters of DOC during the growing season. After estimating seasonal water inflows as the sum of outflow and evapotranspiration (9200 m 3 ha −1 ; Lourence and Pruitt, 1971) and estimating growing season influx using average seasonal DOC concentrations in supply canals, rice fields received more DOC than they exported during the growing season. Based on this simple calculation of inflow, which does not account for percolation losses, the average growing season net import of DOC was 13 kg ha −1 Other surface irrigation systems in California have also been shown to result in a similar net import of DOC to the system (21.4 kg ha −1 ; Poch et al, 2006).…”