The number of acres of sub-surface drip irrigation (SDI) is growing in the Texas High Plains (THP). Some producers claim cotton production yields of 4-5 bales acre-1 using this method of irrigation. However, little research has been done to determine best management practices under SDI and with limited irrigation. Since 2004, a field study at the ARS Plant Stress and Water Conservation Laboratory in Lubbock, Texas has investigated cotton lint yields using SDI. We observed the growth patterns of two cotton varieties (Paymaster HS-26 and Fiber Max 958) on four water treatments (dryland, 2.5, 5.0, and 7.5 mm irrigation day-1). Measurements have focused on root growth, transpiration, and soil wetting patterns around the drip line. Transpiration data from 2005 suggested that the water use efficiency (WUE) of the low (2.5 mm day-1) irrigation treatment was larger than the high (7.5 mm day-1) treatment. We speculate that the different water regimes and varieties combined in such a way to promote a more favorable root growth in the upper portion of the soil profile thus influencing the use of rainwater.