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Research Project: Optimizing the Management of Irrigated Cropping Systems in the Lower Mississippi River Basin

Location: Delta Water Management Research

Title: The effects of alternate wetting and drying irrigation on water use efficiency in Mid-South rice

Author
item REAVIS, COLBY - US Department Of Agriculture (USDA)
item Reba, Michele
item RUNKLE, BENJAMIN - University Of Arkansas

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2024
Publication Date: 5/17/2024
Citation: Reavis, C., Reba, M.L., Runkle, B.R. 2024. The effects of alternate wetting and drying irrigation on water use efficiency in Mid-South rice. Agricultural and Forest Meteorology. 353(110069):1-21. https://doi.org/10.1016/j.agrformet.2024.110069.
DOI: https://doi.org/10.1016/j.agrformet.2024.110069

Interpretive Summary: Rice is flooded a majority of the growing season, which results in high rates of water use in the fields. Canopy water use is divided into evaporation from open water and transpiration from plants as they undergo photosynthesis. Irrigation practices, like alternate wetting and drying (AWD), can change the portion of water used as evaporation and transpiration. Transpiration is important when determining the impacts of drying. A decline in transpiration could be a sign of plant stress, which can negatively impact yields. When deciding the advantages of using a new irrigation method, understanding and quantifying the potential negative impacts is necessary. The aim of this work is to use a new method for estimating transpiration to see if AWD negatively impacted plant water use. The new method links canopy water use and photosynthesis to determine transpiration. Using the method, we saw no signs of stress or negative impacts on canopy water use during drying. Additionally, we saw that plants used approximately 43-53% of the water during the growing season. Producers and extension agents benefit from this work as the results support AWD as a safe irrigation practice in a production setting.

Technical Abstract: Improved water management is a growing need in areas where rice production is intensive. In the state of Arkansas and other portions of the US, new irrigation practices are being implemented to conserve water during production while maintaining high yields. The goal of this study was to evaluate canopy water use in two commercial rice fields using different irrigation practices across three growing seasons. Canopy water use was assessed across multiple metrics, including different representations of water use efficiency (WUE) as well as their contributing terms, gross primary production (GPP) and evapotranspiration (ET). Furthermore, we validated and employed a methodology for estimating transpiration from ET using the concept of underlying water use efficiency (uWUE). To reduce uncertainty associated with canopy transpiration, we compared estimated transpiration using uWUE to two other micrometeorological models, the FAO Penman-Monteith equation using dual crop coefficients (PM56Dual) and the Priestley-Taylor equation as employed by NASA’s Jet Propulsion Laboratory (PT-JPL). The introduction of periodic drying associated with the alternate wetting and drying irrigation practice during the growing season did not have an observable impact on GPP, ET, or transpiration (T). Our findings from the uWUE method indicate that approximately 43 to 53% of ET is released as T during the growing season. The uWUE method improved the relationship between GPP and ET throughout the growing season by scaling using VPD, which accounted for the limitation of VPD on GPP during the afternoon periods. In comparison to other common ET partitioning methods, we observed significant differences in the timing of peak transpiration and the resultant ratio of T to ET (T:ET) with respect to whether GPP or LAI was used to partition ET during the growing season. In all cases, because peak GPP and peak GPP-derived water use precede peak LAI, methods using LAI with no input from GPP typically suggest a later peak in transpiration and transpirative WUE (tWUE) relative to methods incorporating GPP. Despite differences in peak timing, LAI was still able to explain between 73% and 80% of the variability in growing season T:ET.