Estimating Soil Hydraulic Properties Using Pedotransfer Functions in Texas: The Role of Soil Organic Carbon.

Hydrology models have become a primary tool for assessing the effects of land use decisions. A component of hydrology modeling is the soil-plant-water interface, and water movement in this interface is determined by soil hydraulic properties. To model water movement through soil and across landscapes, spatial information on soil hydraulic properties is needed, but these properties are difficult to measure. Traditionally, soil hydraulic properties are estimated by empirical relationships to other soil properties, such as particle size distribution (texture), that are easier to measure and hence can be obtained at finer spatial resolutions. While soil scientist know that soil organic matter is an important factor in soil, current hydraulic model predictions do not take organic matter into consideration. New releases of fine-resolution spatial data on soil organic matter product may provide an opportunity to improve estimates of soil hydraulic properties. The overall goal of this project was to assess the impact of using soil organic matter content to improve estimates of water contents (field capacity and permanent wilting point) and soil porosity on a Texas-wide dataset. I analyzed the effect of organic matter on the soil water contents and porosity estimates by comparing multiple linear regression predictions calculated with organic matter and without organic matter to actual measurements. In general, organic matter was found not to have a significant effect on field capacity or permanent wilting point estimates; however, estimates of porosity were significantly improved by including organic matter into the prediction model. The results indicate that organic matter needs to be incorporated to improve model prediction of soil porosity, however the lack of improvement on the water content estimate indicates that other soil properties might be more important to evaluate and map spatially.