GEOPHYSICAL STUDIES OF THE CHARACTERISTICS OF FLUVIAL AND DESERT SOILS IN WEST TEXAS AND SOUTHERN NEW MEXICO

Agriculture in aridlands, such as in the Rio Grande Valley in west Texas, relies on flood irrigation. However, irrigation can be a major emitter of greenhouse gases by releasing CO₂ and causes salt buildup in the soil. The effects of irrigation are controlled, in part, by soil grain size, larger scale soil structures (e.g. layering, abandoned channels) and mineralogy. A variety of shallow geophysical methods such as ground penetrating radar (GPR), ground conductivity, magnetics, seismic and resistivity, will be utilized to investigate the grain size, mineralogy and larger scale structures at 3 field sites in west Texas and southern New Mexico. The first site is a managed pecan orchard, located near Tornillo, TX. The second site is a relatively undisturbed water well-field near Canutillo, TX. The third site is a natural desert located in the Jornada Experimental Range northeast of Las Cruces, NM.

As a first step, we evaluated previously collected DC resistivity (Ohm-mapper, multi-electrode DC) and soil conductivity (EM31) studies within the pecan grove and compared these geophysical surveys to borehole measurements of grain size, soil geochemistry, soil gas composition and tree size/growth to reveal how the variation of soil properties influences water drainage and salt build up at the site. These data will help guide the collection of additional GPR, resistivity and seismic data at the site as well as the other 2 sites. Our results will help provide insight into which geophysical techniques will be best for characterizing soil properties controlling salt build up, CO₂ emission and plant growth in flood irrigated fields in arid regions.