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

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 rice cultivation. 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) that includes a sensitivity to vapor pressure deficit (VPD). Periodic drying associated with the alternate wetting and drying irrigation practice did not result in decreased GPP, ET, or transpiration (T). Our findings indicated that approximately 43 to 56 % of ET is released as T during the growing season. The uWUE method improved the relationship between GPP and ET by accounting for the limitation of VPD on GPP during the afternoon periods.