Impacts of Alternate Wetting and Drying and Delayed Flood Rice Irrigation on Growing Season Evapotranspiration

Abstract:

Alternate wetting and drying (AWD) is an irrigation practice used in rice production that has potential to decrease the amount of water applied during the growing season. Strategic drying during the growing season allows producers to better capture rain events to offset field water demand. However, there are concerns with how drying during the growing season will impact plant growth and yield. We observe ET as an indicator of canopy productivity across three growing seasons between two fields under different combinations of AWD and conventional delayed flood (DF) treatment. Our results indicate that there are no significant differences in DF and AWD fields with respect to ET and implied canopy water use, especially during canopy closure (leaf area index; LAI>5). Drying events appeared to only have an observable effect during the early growing season (LAI<0.5). ET was largely energy driven, and there were no observable limitations placed on its process based on observed vapor pressure deficit, soil moisture, and above-canopy air temperature throughout the daytime period. Investigations into canopy conductance based on ET observations show no observable or consistent controls of local biometeorological drivers (net radiation, vapor pressure deficit, temperature) on canopy water transport, likely due to uninhibited plant access to water. We observe similar lack of response when observing conductance based on CO₂ exchange using the Ball-Berry approach. We conclude that, if properly managed, AWD is a suitable practice that does not noticeably inhibit water exchange between the canopy and atmosphere. To further analyze the measures of plant health, we provide insight on the development and application of conductance-based models used to estimate ET and CO₂ fluxes in rice in the Mid-South region.