Evaluating and Validating the Soil Vulnerability Index (SVI) and Leaching Index (LI) Across Diverse Bio-Physical Regions in the United States.

Major concerns from agricultural lands in the United States include soil erosion and nutrient loss from surface runoff and sub-surface flows. The NRCS proposed the Soil Vulnerability Index (SVI) and the Leaching Index (LI) to evaluate inherent vulnerability of soils to runoff-induced soil erosion and sediment loss, and loss of nutrients in subsurface flows. The SVI is derived using hydrologic soil group (HSG), slope, and K-factor (soil erodibility factor) while LI also accounts for organic soil. The goal of this study is to evaluate SVI and LI for quantifying the inherent vulnerability of soils to sediment and nutrient loss in agricultural lands with differing physiographic and hydrogeomorphic characteristics within the United States. Altogether nine different sites in the central US (Missouri, Iowa, Arkansas, Mississippi) and the eastern US (Pennsylvania, Georgia, Maryland) were selected. Drainage area for sites ranged from 6 to 1048 km2.  A preliminary analysis, including risk mapping, was performed to evaluate SVI and LI. In most of the sites, the SVI and the LI identified the most vulnerable areas, thereby assisting in determining areas that are in need of improved conservation and management practices. Notable exceptions for SVI included areas with HSG-A, slope >4% and HSG-D, and slope >6% and HSG-B or HSG-C. Exception for LI included areas with slope >12%. Areas with slope <2% were not properly assessed using SVI and LI. Highly gullied areas are not assigned any HSG in SSURGO, therefore could not be categorized. The SVI and the LI have potential to be effective indices in categorizing soils inherent vulnerabilities to runoff and leaching, and thus in planning for conservation practices. They are expected to be used by local stakeholders to identify areas inherently vulnerable to erosion and nutrient loss; and to improve land management decisions.