Geographic Patterns of Soil Water‐Holding Capacity in the Contiguous United States

Abstract

AbstractThe geographic patterns of soil water‐holding capacity are important for studying the response of vegetation and water supply to climate change. This study was conducted to evaluate which dataset to use for national‐scale water balance modeling. Spatial databases of soil properties for the contiguous USA were derived from the USDA national soil database (NATSGO) and the United Nations soil map of the world. The NATSGO data generally resulted in finer textures, greater rock fragment content, and more shallow soils. The organic matter content in the surface was similar, but the NATSGO database did not contain sufficient information to estimate organic matter content of the lower soil. The Rawls model was used to estimate soil water‐holding capacity of the 0‐ to 50‐cm depth from particle‐size distribution, organic matter content, rock fragment content, and soil depth data. The Saxton model was used to estimate the water‐holding capacity of the 50‐ to 150‐cm depth interval, because it didn't require organic matter data. The water‐holding capacity in the surface layer based on the NATSGO data was larger than that based on the soil map of the world despite greater rock fragment contents and shallower soil depths. There were few similarities in the water‐holding capacities of the 50‐ to 150‐cm depth layer because of large differences in rock fragment content and soil depth. The NATSGO dataset is recommended because the map unit composition was based on a statistical framework with a large sample size and it better characterizes rock fragment content and soil depth.