Simulated Crop-Growth-Stage-Based Deficit Irrigation Strategies for Cotton for Increasing Water Productivity and Net Returns

Water saving in irrigation is of utmost importance in the Texas High Plains (THP) region because of rapidly declining groundwater levels in the underlying Ogallala Aquifer and increasing variability in weather. This study was aimed at suggesting efficient crop-growth-stage-based deficit irrigation strategies for cotton (Gossypium hirsutum L.) based on simulated cotton yield, irrigation water use efficiency (IWUE), water productivity (WP) and net returns under long-term weather conditions. The CROPGRO-Cotton module available in the Decision Support System for Agrotechnology Transfer (DSSAT) Cropping System Model was used in this study, which is designed for a center pivot irrigation system. Five growth stages, namely, germination and seedling emergence (GS1), squaring (GS2), flower initiation/ early bloom (GS3), peak bloom (GS4), and v) cutout, late bloom and boll opening stage (GS5) were considered in this study. Applied seasonal irrigation water varied from 260 to 480 mm under five different irrigation-scheduling scenarios. Under each scenario, six crop-growth stage-based irrigation treatments were adopted (irrigation skipped in each of the five growth stages in the first five treatments and irrigation was applied in all growth stages in the sixth treatment), resulting in a total of 30 irrigation strategies. The peak bloom growth stage (GS4) was found to be the most sensitive stage to water stress, and imposing water deficit during this stage resulted in the lowest cotton yield, IWUE, WP and net economic returns under all weather conditions. In general, irrigation treatment in which irrigation was skipped during GS1 growth stage was found to be the best irrigation treatment for maximizing seed cotton yield, IWUE, WP and net returns. Overall, results showed that higher crop WP and net returns could be achieved with the application of about 360, 420 and 480 mm of irrigation water in wet, normal and dry years, respectively, through appropriate crop-growth-stage-based deficit irrigation strategies.