Crop Coefficient Curve for Paddy Rice from Residual Energy Balance Calculations

Abstract

The crop coefficient (K c) values of rice paddy are important for estimating accurate rice crop evapotranspiration (ET c), water transfers planning, efficient irrigation management, and hydrological studies. In this study, ET c was measured and a generalized K c curve was calculated for paddy rice in the Sacramento Valley, California. Field experiments were conducted in three rice paddy fields during the 2011-2013 growing seasons. Surface renewal analysis, after calibration using eddy covariance method, was applied to obtain sensible heat flux values from high-frequency temperature readings; latent heat flux densities were characterized by the residual of the energy balance method. The results revealed that there is considerable variability in rice water use both spatially and temporally. The average 3-year measured seasonal ET c of the experimental fields ranged from 690 to 762 mm in Butte County and from 681 to 813 mm in the Colusa County. A mean daily seasonal ET c of 5.3 mm d −1 and midseason ET c of 5.8 mm d −1 was observed. The rice K c values were lower than those commonly used to estimate rice ET c during the midseason and were greater than expected during early growth before canopy closure. For a typical growing season of 145 days, the K c values were estimated as 1.10, 1.00, and 0.80 for the initial-growth, midseason, and late-season stages, respectively. The generalized K c curve is quite accurate for practical application and enables growers to determine rice crop water use in a reliable, usable, and affordable format. The proposed K c information can be used to refine the estimates of rice consumptive water use in the Sacramento Valley for the purpose of water transfers to water-short areas of the State. These K c values are likely applicable to other locations having similar climate to the Sacramento Valley in California.

Actual Evapotranspiration and Tree Performance of Mature Micro-Irrigated Pistachio Orchards Grown on Saline-Sodic Soils in the San Joaquin Valley of California

“…Agriculture 2019, 9, x FOR PEER REVIEW 7 of 20 Figure 2 shows an example of the scatter of the H versus H' data obtained during the entire 2016 season in the non-saline orchard. Alpha calibrations were calculated separately for unstable conditions (upward fluxes), represented by positive H, and for stable conditions (downward fluxes), represented by negative H. It is well known that unstable conditions enhance turbulence with respect to stable ones, so separate calibration is common in literature [41,45,46].…”

Feasibility of Moderate Deficit Irrigation as a Water Conservation Tool in California’s Low Desert Alfalfa

“…The actual evapotranspiration (ET a ) was measured using the residual of energy balance (REB) method with a combination of surface renewal (SR) and eddy covariance (ECov) techniques. The SR and ECov are well-recognized methods to estimate the sensible heat flux density (H) and to calculate the latent heat flux density (LE), using the REB approach [23][24][25][26][27][28].…”

“…The SR H and the ECov H were used to determine the LE values. The advantage from using both the ECov and SR methods was that they are independent and similar results provide a high level of confidence in the data used [26,28,29]. Latent heat flux density was calculated using the Residual of Energy Balance equation, as follows:…”

Evaluation of Surface Renewal VS. Eddy Covariance Methods to Estimate Cereal Crops Evapotranspiration

“…Similar to "ETc-SR" at the initial stage, the "ETc-EC" was higher than "ETc-FAO", with "RMSE" of 0.88 mm/day and 18.68% "NRMSE", then the "ETc-EC" values become lower than the "ETc-FAO" during mid-season and lateseason growth stages, by "RMSE" values equal to 0.74 and 0.35 mm/day and "NRMSE" values equal to 13.82% and 7.33% for each season, respectively. Montazar et al (2017) explained the observed high values of the "ETc" determined by "REB" methods, at the beginning of the flooded rice season, as a result to the small canopy cover proportional to the water surface in the flooded field, that in this case the surface area of the water exposed to the weather conditions are higher than the area of the plants canopy, which produce higher "LE". As the size of rice canopy increases, it covers the water surface, and avoid the effect of the water surface in the "LE" values.…”