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Effects of irrigation level and timing on profile soil water use by grain sorghum

Bell, Jourdan M., Schwartz, Robert C., McInnes, Kevin J., Howell, Terry A., Morgan, Cristine L.S.
Agricultural water management 2020 v.232 pp. 106030
Sorghum bicolor, crop yield, deficit irrigation, developmental stages, drought, grain sorghum, growing season, irrigation rates, irrigation scheduling, plant available water, rooting, water stress, High Plains (United States), Texas
Although deficit irrigation (DI) may have the potential to optimize crop yields in water limited environments, the success of such strategies may depend on the ability to manage variability in profile stored soil water during periods of drought. Understanding variability in stored soil water and crop rooting depth is an important component of successfully managing a deficit irrigation strategy. Traditionally, DI is applied at a fraction of the full irrigation (FI) requirement, but managed deficit irrigation (MDI) may optimize yield and irrigation by coordinating irrigation timing with the crop’s reproductive stages through the management of soil water depletion and water stress. The depth of the soil water use by grain sorghum [Sorghum bicolor (L.) Moench] was evaluated in the High Plains of Texas, USA under FI, DI, and MDI strategies: during the 2010–2012 growing seasons. Crop water use during critical growth stages was year specific due to variable precipitation and antecedent soil moisture even though irrigation strategies were maintained as planned in all years. In 2010, soil water contents within the rooting zone (0–1.6 m) were > 50 % of the potential plant available water (PPAW) in the soil at emergence under all treatments, and soil water contents remained > 50 % PPAW at half-bloom for FI and MDI. Soil water contents were < 50 % PPAW at half-bloom for both DI and MDI in 2011 and 2012. In 2011, water contents only remained> 50 % PPAW under FI from 0- to 0.6-m through the growing season. Due to variability in the depth of the stored soil water, irrigation scheduling based on managed allowed depletion below PPAW may need to be modified to account for greater sparse root densities deeper in the profile.