Evaluation of the Soil Vulnerability Index for artificially drained cropland across eight Conservation Effects Assessment Project watersheds

Authors: Baffaut, Claire; LOHANI, SAPANA - University Of Nevada; THOMPSON, ALLEN - University Of Missouri; DAVIS, AUSTIN - University Of Missouri; ARYAL, NIROJ - North Carolina Agricultural And Technical State University; Bjorneberg, David - Dave; Bingner, Ronald - Ron; Dabney, Seth; DURIANCIK, LISA - Natural Resources Conservation Service (NRCS, USDA); James, David; King, Kevin; LEE, SANGCHUL - University Of Maryland; McCarty, Gregory; PEASE, LINDSAY - University Of Minnesota; Reba, Michele; Sadeghi, Ali; Tomer, Mark; Williams, Mark; Witthaus, Lindsey

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2019
Publication Date: 1/1/2020
Citation: Baffaut, C., Lohani, S., Thompson, A., Davis, A.R., Aryal, N., Bjorneberg, D.L., Bingner, R.L., Dabney, S.M., Duriancik, L.F., James, D.E., King, K.W., Lee, S., McCarty, G.W., Pease, L.A., Reba, M.L., Sadeghi, A.M., Tomer, M.D., Williams, M.R., Yasarer, L.M. 2020. Evaluation of the Soil Vulnerability Index for artificially drained cropland across eight Conservation Effects Assessment Project watersheds. Journal of Soil and Water Conservation. 75(1):28-41. https://doi.org/10.2489/jswc.75.1.28.
DOI: https://doi.org/10.2489/jswc.75.1.28

Interpretive Summary: EThe Soil Vulnerability Index (SVI) utilizes soil properties and topographic slope to classify inherent vulnerability of cropland to loss of sediment and nutrients by runoff and leaching. Management is not taken into account in this classification, except for the presence of artificial drainage. When cropland is artificially drained by any means, vulnerability to leaching is raised by two classes out of four while vulnerability to runoff remains unchanged. There is a need to assess SVI when drainage is present, across a range of regions and drainage methods. The objectives of this evaluation were to determine whether: 1) SVI vulnerability assessment for runoff and leaching matched expert assessment, and 2) SVI could be improved. SVI was evaluated for eight sites where soil drainage was present. Seven watersheds, ranging in size from 600 to 113,600 ha, all had cropland with rotations including row crops or small grains. The eighth site consisted in six pairs of fields with and without a specific practice. Overall, vulnerability to runoff and leaching was considered adequate for sites with subsurface drainage and with climate similar to what exists in the Upper Mississippi and Ohio-Tennessee River Basins, which was the region used for the development of SVI. Vulnerability assessment did not match expert assessment in case of surface drainage (with surface ditches) and when rain intensities were different from those typically found in the Upper Mississippi and Ohio-Tennessee River Basins. In addition, soil map units that include several components can cause misevaluation of vulnerability at field scale in drained situations. Meanwhile, at watershed or regional scale, the leaching component should be considered both with drainage and without drainage so that the causes of the vulnerability (permeable soils or artificial drainage) can be distinguished.

Technical Abstract: The Soil Vulnerability Index (SVI) classifies inherent vulnerability of cropland to loss of sediment and nutrients by runoff and leaching and is linked to soil properties and topographic slope. Management is not taken into account in this classification, because it is not readily feasible with the lack of a national database, except for the presence of surface or subsurface drainage. When cropland is artificially drained by any means, vulnerability to leaching is raised by two classes out of four while vulnerability to runoff remains unchanged. There is a need to assess SVI when drainage is present, across a range of physiographic regions and drainage methods. The objectives of this evaluation were to determine whether: 1) SVI vulnerability assessment for runoff and leaching matched expert assessment, and 2) SVI could be improved. SVI was evaluated for eight sites where soil drainage was present. Seven watersheds, ranging in size from 600 to 113,600 ha, all had cropland with rotations including row crops or small grains. The eighth site consisted in six pairs of fields with and without a specific practice. Overall, vulnerability to runoff and leaching was considered adequate for sites with subsurface drainage and with climate similar to what exists in the Upper Mississippi and Ohio-Tennessee River Basins, which was the region used for the development of SVI. Vulnerability assessment did not match expert assessment in case of surface drainage and when rain intensities were different from those typically found in the area used for SVI development. In addition, complex soil map units can cause misevaluation of vulnerability at field scale in drained situations. Meanwhile, at watershed or regional scale, the leaching component should be considered both with drainage and without drainage so that the causes of the vulnerability (permeable soils or artificial drainage) can be distinguished.