Evaluation of growth-stage-based variable deficit irrigation strategies for cotton production in the Texas High Plains

Irrigated agriculture in the Texas High Plains (THP) region faces severe challenges due to rapidly declining groundwater levels in the underlying Ogallala Aquifer, recurring droughts, and projected warmer and drier future climatic conditions. Scheduling irrigation with appropriate deficits in different crop growth stages could improve irrigation water use efficiency (IWUE), and thereby enable additional savings in valuable groundwater without severely compromising the crop yield. Our objective was to identify efficient growth-stage-based variable deficit-irrigation (GS-VDI) strategies for cotton production in the THP region. For this purpose, we used an evaluated Decision Support System Agrotechnology Transfer (DSSAT) CROPGRO-Cotton model based on measured data from a cotton IWUE field experiment conducted at Texas A&M AgriLife Research Center at Halfway, TX, in the THP region. This study considered four growth stages: (i) first leaf to first square (GS1), (ii) flower initiation/ early bloom (GS2), (iii) peak bloom (GS3), and (iv) cutout, late bloom, and boll opening stage (GS4). Long-term (1977 - 2019) simulations were conducted with four deficit levels (30%, 50%, 70%, and 90% evapotranspiration [ET] replacements) implemented in the above described four different growth stages, resulting in 256 combinations of deficit-irrigation scenarios. Based on the results of simulated seed cotton yield and IWUE, efficient GS-VDI strategies were suggested for dry, normal, and wet years. For example, a strategy of 90% ET-replacement in GS1 to GS3 and of 30% ET-replacement in GS4 was found to be an ideal strategy in normal years to achieve higher seed cotton yield (similar to 8% less than that for the baseline scenario with 100% ETreplacement implemented in all growth stages) while saving 65 mm of irrigation water. Results from this modeling study provide useful recommendations on appropriate irrigation management strategies for sustaining cotton production under different weather conditions while conserving valuable groundwater resources of the Ogallala Aquifer.