Effects of Deficit Irrigation on Plant Available Water, Cotton Root Growth, and Cotton Yield in the Rio Grande Plains of Texas John Shallock, Diane L. Rowland, Cristine L.S. Morgan, T.D.A. Forbes, and Bethany Speer ABSTRACT Water conservation in South Texas is crucial for preserving the region’s ecological and economic resources. Improving our understanding of the relationship between crop physiology and soil physical properties can improve management of these agricultural systems, particularly in areas supported by the Edwards Aquifer, which also supplies water to San Antonio, TX. The purpose of this study is to identify the effects of deficit irrigation on plant available water, root growth, and crop yield. Cotton (Gossypium hirsutum) was planted at the Texas AgriLife Research Center in Uvalde on approximately 4.38 hectares and irrigated with a Low Energy Precision Application center pivot system. Three irrigation regimes were implemented, including full irrigation at 100% of crop need, deficit irrigation at 70% of crop need, and primed acclimation, which provides 70% of needed water from the time of planting until flowering, and then delivers 100% for the remainder of the growing season. Two tillage treatments were implemented: strip till and conventional till. Neutron scattering was used to measure soil moisture to a depth of 100 cm, and a minirhizotron camera was used to quantify root development over the course of the season. Physiological response was monitored with respect to irrigation and tillage type.