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ARS Home » Southeast Area » Jonesboro, Arkansas » Delta Water Management Research » Research » Publications at this Location » Publication #331434
Title: Evapotranspiration measurement and modeling in Mid-South irrigated rice

Author
item FONG, BRYANT - Orise Fellow
item Reba, Michele

Submitted to: United States Committee on Irrigation and Drainage Conference
Publication Type: Proceedings
Publication Acceptance Date: 9/19/2016
Publication Date: 10/14/2016
Citation: Fong, B., Reba, M.L. 2016. Evapotranspiration measurement and modeling in Mid-South irrigated rice . United States Committee on Irrigation and Drainage Conference. 15-30.

Interpretive Summary: Nearly 75% of US rice is grown in the humid mid-South. Rice requires more water to produce than other crops (corn, soybean, and cotton). The identification of how rice uses water is paramount to understand regional water use and water allocation. Drill-seeded, commercial sized rice fields in Northeast Arkansas were observed under two irrigation managements: continuous flood (CF) and alternate wetting and drying (AWD) in the 2013 and 2015 production seasons. Two eddy covariance (EC) systems were used to measure water vapor loss or evapotranspiration (ET). Measured ET compared to existing models that are often used to help schedule irrigation. These models underestimated and overestimated flux under different field conditions. Daily ET decreased 25-45% with removal of the floodwater, indicating ET was influenced by climate and management practices. AWD reduced ET demand during draw down events due to decreased evaporation. Findings from this research will help inform irrigators and extension personnel involved in irrigation planning on how to adjust management and tools for differences in irrigation strategy in rice.

Technical Abstract: Nearly 75% of US rice is grown in the humid mid-South. Rice requires more water to produce than other crops (corn, soybean, and cotton). The identification of rice evapotranspiration and irrigation demand is paramount to understand regional water use and water allocation. Drill-seeded, commercial sized rice fields in Northeast Arkansas were observed under two irrigation managements: continuous flood (CF) and alternate wetting and drying (AWD) in the 2013 and 2015 production seasons. The initial flood after post nitrogen fertilizer application occurs at the same time in CF and AWD. After two weeks AWD fields are permitted to dry intermittently. Two eddy covariance (EC) systems were used to measure evapotranspiration (ET) and CO2 flux. Measured ET from the EC method was compared to Penman-Monteith/FAO56 and Hargreaves models. The Penman-Monteith model underestimated flux by 5% possibly due to energy gap closure bias from soil heat flux or high humidity. The Hargreaves model overestimated flux especially on cloudy and rainy days. Both models show bias early and late in the production season as field conditions changed from non-flooded to flooded conditions. Daily ET decreased 25-45% with removal of the floodwater indicating ET may be influenced more by climate and management practices than growth stages. AWD reduced ET demand during draw down events due to decreased evaporation. There was no significant reduction in yield between AWD and CF.