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Soil Physics and Soil & Water Management & Conservation

Soil Water Regime in Space and Time in a Small Georgia Piedmont Catchment under Pasture

USDA-ARS, J. Phil Campbell Sr. Natural Resource Conservation Center, 1420 Experiment Station Road, Watkinsville, GA 30677

^* Corresponding author (dendale{at}uga.edu)

Soil water influences hydrological, biological, and biogeochemical processes that determine on- and off-site response of landscapes under different agricultural uses. There are relatively little detailed spatial and temporal soil water measurements to validate current representations of spatial and temporal soil water variability. Soil water was measured over 3 yr at 12 sites to a 1.2-m depth in a 7.8-ha pasture catchment in the Georgia Piedmont in southeastern USA. The Mahalanobis statistical difference was estimated between all pairs of measurement sites for soil water. Multidimensional scaling of the Mahalanobis differences showed that only a single statistical dimension was separating the observed soil water variations at measurement sites (r = 0.99). This statistical dimension was then found to be most closely correlated with the depth to the Bt and the depth of the Ap horizons for explaining the observed variation in soil water between sampling sites (r = 0.69 and r = 0.8, respectively). Those sites where the Bt, an argillic horizon, was close to the surface, even when higher up the landscape, were generally wetter than those in which the Bt was deeper, even in the lower part of the landscape. The depth to the Bt horizon may serve as an indicator of the portions of the watershed most likely to be primary sources of runoff in association with the depth of overlying coarse-textured soil. Volumetric soil water content was generally greatest in winter (22 to 30% average) and least in summer (8 to 12% except when influenced by intense summer storms). To fully understand the soil water dynamics of Piedmont or similar landscapes, it is important to know the spatial distribution of the depth to the Bt horizon. Improved understanding of the soil water dynamics could lead to improved land use decisions, erosion control, and management of water resources. This should be of interest to many researchers across many disciplines.

Abbreviations: MD, Mahalanobis distance • MDS, multidimensional scaling • TDR, time domain reflectometry