Investigation into rainwater use by cotton under multiple irrigation management conditions in the Texas High Plains

Irrigation management practices in the Texas High Plains (THP) might be improved if we could ascertain the proportion of rainfall utilized by the crop in any given rainfall event. For instance, the primary source of irrigation water in the THP is pumped from the Ogallala Aquifer (OA), and can be enriched in ¹⁸O compared to rainfall-captured water. Given this expected difference, it should be possible to determine if the crop is utilizing the water from a rainfall event. To this end, cotton was grown using three irrigation management practices: subsurface drip, center pivot, and no irrigation (dry land). The water used for irrigation was pumped from the Ogallala aquifer, and rainfall was gathered in a rain gauge with mineral oil to prevent evaporation. Additionally, plant and soil samples were collected following each precipitation event every two hours and every eight hours respectively. Water was then extracted from the soil and plant samples using cryogenic vacuum distillation, and analyzed for ¹⁸O/¹⁶O ratios using the DLT-100 Liquid-Water Isotope Analyzer from Los Gatos Research Inc. The difference in isotope concentrations in the extracts from soils was used to determine infiltration depth into the soil profile at each location. The isotopic composition of the plant water was used to determine if the was used to compare rainwater use across the different irrigation management practices. Results might suggest changes to the way in which we apply irrigation water that would improve root growth and distribution to enhance the capture of rainfall.