Date of Graduation

8-2017

Document Type

Thesis

Degree Name

Master of Science in Biological Engineering (MSBE)

Degree Level

Graduate

Department

Biological and Agricultural Engineering

Advisor/Mentor

Runkle, Benjamin R.

Committee Member

Haggard, Brian E.

Second Committee Member

Reba, Michele L.

Keywords

Arkansas; Evapotranspiration; Penman monteith; Rice

Abstract

The goal of this study was to evaluate different methods for quantifying evapotranspiration (ET) in commercial rice fields using different irrigation regimes. The rice fields were located in south central Arkansas. The different irrigation regimes were alternate wetting and drying (AWD) and continuous flooding (CF). Alternate wetting and drying and conventional flooding estimates of ET were 602 mm and 570 mm, respectively, based on field observations using eddy covariance. Models used to estimate ET estimated values between 498 and 653 mm for the 2015 growing season. The Penman Monteith actual evapotranspiration model (PM AET) performed best when compared to the eddy covariance field observations from both irrigation regimes using an iteration of the Jarvis model for conductance, which was scaled using field observations of leaf area index (LAI). The Breathing Earth Systems Simulator (BESS), a global product based on remote sensing data, also served as an acceptable method to estimate ET, though its estimated ET of 498 mm indicates a low bias. AWD showed no significant reductions in ET when compared to CF throughout the growing season, including during periods where the AWD field was confirmed to have a water table depth below zero. This pattern was also consistent in observing the PM AET model over the same periods of time. The lack of disturbance in changed ET rates while the water table was fluctuating implies that while the water table was below zero, the rice plants within the AWD field did not experience significant drought stress. Because the AWD plants were able to retain a normal amount of stomatal activity and production, there were also no significant differences in yield (9.42 ± 0.82 t ha-1 in CF, 9.83 ± 1.02 t ha-1 in AWD). These results indicate that AWD did not induce drought stress within the plants while still being able to take advantage of seasonal rain fall to offset pumping costs.

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