Optimizing Subsurface Drip Irrigation in the Texas High Plains.

In the Texas High Plains (THP), irrigated agriculture accounts for half of the cultivated area and > 80% of crop production and gross incomes. This agriculture depends on water extracted from the Ogallala Aquifer, which is declining because withdrawals exceed natural recharge. This fact compromises the aquifer’s long-term sustainability. The purpose of this study was to measure soil water content in an Amarillo soil series under cotton irrigated with subsurface drip (SDI). The objective was to optimize the SDI wetted patterns around emitters through irrigation strategies to increase rainfall harvesting and increase water use efficiency. Soil volumetric water content (VWC) was measured using Time Domain Reflectometry with 30 soil probes in three irrigation treatments (2.5, 5.0, and 7.5 mm d^-1). We also measured soil texture, bulk density, saturated hydraulic conductivity and soil water potential release curves at different locations within treatments. Results show 1) higher bulk density values (1.45 to 1.70 g cm^-3) than expected for this soil (1.35 to 1.50 g cm^-3); and 2) high saturated conductivity (10² to 10³ cm d^-1) in the first 0.35 m soil layer and lower values (< 10 cm d^-1) from 0.35 to 1 m, showing two distinct soil horizons. The effect of these soil properties was clearly observed in the shape of the wetted pattern around drip emitters in all three treatments, i.e., narrow from 0 to 0.35 m soil depth and wide from 0.35 to 1 m soil depth. Further, all of the irrigation events created a 0.4-m wide pattern at a 0.3 m soil depth. Additional field data will be collected, and the Hydrus 2D/3D model will be used to simulate different irrigation strategies to optimize the wetted soil volume around drip emitters, improve rainfall harvesting and increase water use efficiency in the Ogallala Aquifer area of Texas High Plains.