ABSTRACT:

Water availability is crucial for organismal survival and growth in dryland environments, affecting both ecological interactions and carbon dynamics. The goal of this thesis is to develop soil water release curves (SWRCs) that link soil water potentials (Ψ) to soil water content (θ). Using the SWRCs, temporal soil water sufficiency curves are developed, which quantify the amount of time that dryland critical zones have enough water to sustain the physiology of organisms. These curves allow for effectively indicating water availability across different species, coverage types, and soil conditions, enhancing our understanding of water dynamics in drylands and contributing important parameters for a variety of studies. I examine the interaction between water, soil, and plant dynamics at two sites: the Ivey pecan farm in Tornillo, Texas and the Jornada Experimental Range in Las Cruces, New Mexico. I assess physical soil properties, including depth, texture, and ground cover types such as bare ground, creosote, mesquite, and grass. At the Ivey Pecan Orchard, fine and coarse sites were sampled to analyze variations in soil texture. Data from moisture sensors for the period of 2011-2021 were cross-verified with direct soil gravimetric measurements and SWRCs at corresponding depths. A corresponding adjustment in data allowed for accurate quantifications of soil moisture and subsequently conversions of these measurements into water potentials using the Fredlund-Xing (1994) model, thus providing a detailed view of moisture trends across different soil coverages and textures. At the Jornada Experimental Range, it was found that shallow soils at depths of 5 and 10 cm experienced significant increases in water loss (retained water less well), whereas deeper soils exhibited more water retention stability. Our refined data showed that the upper 30 cm of soils under creosote and mesquite shrubs typically maintained water availability above the wilting point of creosote (-6 MPa) only slightly more than 50% of the time. Thus, we conclude that shallow (0-30 cm) soils in the shrubland has insufficient water availability for sustained plant health year-round, which is consistent with seasonal grass dieback at the site. Shrub species, such as creosote and mesquite, likely compensate with access to deeper water sources via their rooting structures. Preliminary correlations of soil moisture data with carbon exchange measured via eddy flux tower were inconclusive, but further modeling could reveal important connections between water sufficiency and net carbon balance. The development of temporal soil water sufficiency curves and their ability to predict water availability for organisms contribute to a broader understanding of organism water availability in drylands. This tool provides a solid foundation for future studies in drylands and works to advance the understanding of soil-plant-atmosphere relations in dryland critical zones.

ABSTRACT:

This data product provides soil hydraulic and texture data from fine- and coarse-textured intensive sampling sites within the Ivey Pecan Orchard in Tornillo, Texas. The orchard is located on floodplain deposits of the Rio Grande with substantial spatial variation in soil texture, and previous work at the site has shown differences in pecan tree size and soil moisture dynamics between fine- and coarse-textured areas. These data were collected to characterize how soil texture influences water retention and water availability in this flood-irrigated dryland agroecosystem. The dataset includes HYPROP/WP4C-derived soil water retention information exported to spreadsheet format, original HYPROP software files, associated diagnostic plots, and PARIO particle size analysis files. Samples represent multiple depths, primarily within the upper 30 cm of soil, with additional deeper samples near 120 cm. Soil water release curves were fit using the Fredlund-Xing model, and the exported HYPROP spreadsheets include fitted model parameters and associated uncertainty estimates. These measurements can be used to relate volumetric water content to soil water potential and to compare water retention behavior between fine- and coarse-textured orchard soils. The dataset provides reusable soil physical parameters for studies of soil moisture dynamics, plant water availability, and soil–plant–atmosphere interactions in flood-irrigated dryland agroecosystems. The dataset was developed as part of Lindsey Dacey’s thesis research, which used soil water release curves to evaluate texture-related differences in soil water availability at the Ivey Pecan Orchard.