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ARS Home » Midwest Area » Columbia, Missouri » Cropping Systems and Water Quality Research » Research » Publications at this Location » Publication #371508
Research Project: Long-term Management of Water Resources in the Central Mississippi River Basin

Location: Cropping Systems and Water Quality Research

Title: Sensitivity of the Soil Vulnerability Index to thin topsoils above a restrictive layer

Author
item Baffaut, Claire
item THOMPSON, ALLEN - University Of Missouri
item DAVIS, AUSTIN - University Of Missouri
item PHUNG, QUANG - University Of Missouri

Submitted to: Soil and Water Conservation Society
Publication Type: Abstract Only
Publication Acceptance Date: 2/19/2020
Publication Date: 7/27/2020
Citation: Baffaut, C., Thompson, A., Davis, A., Phung, Q. 2020. Sensitivity of the Soil Vulnerability Index to thin topsoils above a restrictive layer [abstract]. Soil and Water Conservation Society International Annual Conference, July 26-29, 2020, Des Moines, Iowa.

Interpretive Summary:

Technical Abstract: Soil vulnerability describes the risk of sediment and nutrient losses into surface and ground waters when land underlain by that soil is cultivated. The Soil Vulnerability Index (SVI) developed by the Natural Resources Conservation Service ranks this vulnerability. The SVI uses slope and SSURGO soil properties such as erodibility, hydrologic soil group, fraction of coarse fragments, classification as an organic soil, and presence of artificial drainage. Previous investigations highlighted limitations of the SVI in the case of a thin layer (< 4”) above a substrate or a restrictive soil layer because 1) hydrologic processes or farm operations may expose the second layer, and 2) a thin topsoil above a restrictive layer may bring additional risks of nutrient and soil losses. Therefore, the objectives of this study were to: 1) evaluate the effect on SVI of using the soil properties of the second layer when the first layer is less than 4” thick, and 2) evaluate the need for additional considerations when thin topsoils are present. The study included four Conservation Effects Assessment Project (CEAP) watersheds in Idaho, Missouri, Pennsylvania, and Maryland, selected for the presence of soils with topsoil above a restrictive layer. Methods to assign missing erodibility and coarse fragment content were proposed and evaluated. Preliminary comparison of SVI calculated with first and second layer soil properties showed that changes were either negligible or in the direction of increasing vulnerability to runoff and leaching. Sediment yields within each studied watershed were simulated using the Soil and Water Assessment Tool (SWAT) and the Annualized Agricultural Non-Point Source Pollution Model (AnnAGNPS). Sensitivity of the results to the thickness of the topsoil layer will guide how to include the effect of a thin topsoil layer into the SVI classification.