Purpose, development, and synthesis of the Soil Vulnerability Index for inherent vulnerability classification of cropland soils

The Soil Vulnerability Index (SVI) was developed by the USDA Natural Resources Conservation Service (NRCS) to classify inherent vulnerability of cropland soils based on field sediment and nutrient transport resulting from surface runoff and leaching. The primary purpose of the SVI is to aid conservation planners in more rapidly assessing managed lands and inherent resource concerns. The index is based on hydrologic soil group, slope, and soil erodibility for cultivated cropland soils, with the addition of percentage rock fragments and organic matter when considering leaching. Although the SVI is intended for use throughout the United States, its development was based on the physiographic and rainfall characteristics of the Upper Mississippi and Ohio-Tennessee River basins. The purpose of this study was to evaluate the SVI in areas both in and outside of the area for which it was developed. Thirteen different watersheds were selected to conduct this evaluation. Vulnerability classifications using the SVI were compared with those from on-site experts9 knowledge and with model simulations using local data. Four companion papers in this special collection discuss SVI classification based on the effects of land slope, artificial drainage, sediment and nutrient loads, and vulnerability assessment using hydrologic simulation models. Using results from the various sites, the objective of this paper was to synthesize the interpretation of the value and applicability of SVI vulnerability classification to sediment and nutrient loss across various physiographic regions and suggest where improvement in the SVI could be made.