Water Resources Research Act Program

Details for Project ID 2015AR365B

REWARD: Rice Evapotranspiration and Water use in the Arkansas Delta

Institute: Arkansas
Year Established: 2015 Start Date: 2015-03-01 End Date: 2016-02-29
Total Federal Funds: $25,000 Total Non-Federal Funds: $50,000

Principal Investigators: Benjamin Runkle

Abstract: A faculty research project, “REWARD: Rice Evapotranspiration and Water use in the Arkansas Delta”, is aimed to resolve uncertainties in the water budget as rice farms transition from conventional to alternate wetting-drying irrigation strategies. This project will generate a comparison of five different experimental and modeling methods that estimate evapotranspiration from a pair of companion production rice fields under different irrigation regimes. The product will be a careful water balance across the growing season for these two fields, ready to enact as a model validation tool. The five measurement methods each have different uncertainties associated with their use at different time frames and environmental conditions, so a cross-comparison will significantly reduce the overall uncertainty of the ET estimate. The methods will also generate predictive, model-ready relationships between ET and its driving atmospheric variables (such as humidity and temperature), field moisture status, crop growth stage, and other factors. The five methods proposed to quantify ET are: i. Modeling based on the Penman-Monteith equation, ii. Atmometers and crop-coefficients, iii. The diurnal cycle of water table fluctuations, iv. Eddy covariance, v. Water balance residual. This project will be performed on the private farm owned and managed by the Isbell Family outside of England, Arkansas (3435'8.58"N 9144'51.07"W). The Isbell farm has a history of scientific partnership and involved cooperation with researchers from the Rice Research and Extension Center. This degree of involvement has included co-authorship in peer-reviewed publications. The farm team can provide extensive logistical and practical support, including the use of machinery, storage facilities, and provision of a safe working environment. This project will resolve research gaps that have thus far prevented a full understanding of the effect of water-saving irrigation practices on all components of the water balance. In particular, due to the difficulty of measuring ET, this important term of the water budget is often estimated through empirical coefficients. Eddy covariance and other ET measurements of rice grown elsewhere in the world may not be directly applicable to the situation in Arkansas due to the many differences in cultivation, climate, and soil characteristics. The project will enhance the current body of knowledge on estimating ET through its comparative, multi-method approach. ET is known to be difficult to measure without error or bias, and the best-practice recommendation is to incorporate rigorous quality assessment and quality control procedures. Results of this research will also assist in creating global-scale estimates of the footprint of irrigation on groundwater supplies. As one of the largest irrigation regions in the United States, the Arkansas Delta and alluvial Mississippi aquifers must contribute adequate and reliable data for model validation efforts. The REWARD project will contribute a valuable dataset to these initiatives.