Deep Tillage and Gypsum Amendments on Fully, Deficit Irrigated, and Dryland Soybean

A major limitation to soybean [Glycine max (L.) Merri.] yield is the availability of water for crop production; however, water available for irrigation is declining in many of the crop growing regions. The objectives of this study were to validate and/or refine current allowable deficit recommendation for evapo-transpiration (ET)-based irrigation scheduling for furrow irrigated soybean and to examine the effects of deep tillage and gypsum amendment on yields and water use efficiency (WUE). This experiment was conducted near Stuttgart, AR, across three growing seasons on a soil type described as a fine, smectitic, thermic Typic Albagualf. The soil management treatments were deep tillage, deep tillage/gypsum application, conventional tillage/gypsum application, and conventional tillage. Irrigation treatments (fully irrigated, +1 deficit, +2 deficit, and non-irrigated), were replicated three times within each soil treatment. Increases in soybean yields above 20% (2013), 9% (2014), and above 10% (2015), were observed in the deep tillage treatments. No yield benefits were observed in the gypsum amendment treatments. The +1 deficit resulted in reduction of irrigation water used and can be used in conjunction with deep tillage to obtain similar yield responses as fully irrigated treatments. In conventional treatments reduction in yield was observed at all levels of irrigation deficit except for fully irrigated treatments, indicating that conventional soil management practices should follow Arkansas allowable deficit recommendation for ET-based irrigation scheduling as a maximum allowable deficit to prevent yield loss.