Assessment of Deficit Irrigation Strategies for Cotton Production in the Texas High Plains

Texas High Plains (THP) is an important agricultural region in the United States and it contributes to about 25% of the US cotton (Gossypium hissutum L.) production. Production of cotton in the THP region depends mainly on irrigation with groundwater from the underlying Ogallala Aquifer. However, rapidly declining groundwater levels in the aquifer and increasing pumping costs pose challenges for sustainability of irrigated cotton production in this region. The main objective of this study was to assess the sensitivity of cotton crop to water stress during five critical growth stages and identify appropriate crop-growth-stage-based deficit irrigation strategies for maximizing irrigation water use efficiency (IWUE) and cotton yield during 1978-2016 using the CROPGRO-Cotton module available in the Decision Support System for Agrotechnology Transfer (DSSAT) Cropping System Model (CSM). Critical cotton growth stages considered in this study include: i) germination and seedling emergence, ii) squaring, iii) flower initiation/early bloom, iv) peak bloom, and v) cutout, late bloom and boll opening stage. The amount of seasonal irrigation water applied under seven different irrigation scenarios varied from 120 to 600 mm with three different irrigation application rates of 3, 6 and 10 mm/day, and a total of six treatments (5 treatments in which irrigation was turned off in one of the five critical growth stages and the sixth treatment in which irrigation was applied during all critical growth stages) were implemented, resulting in a total of 42 treatments. The simulated results from this study revealed that water deficit imposed during initial stages of growth (germination and seedling emergence) or after the peak bloom stage did not contribute much towards increasing IWUE and cotton yield. Water stress during peak bloom growth stage caused greater losses in cotton yield and IWUE, because of the high demand of water in this stage.