DO SOIL SURVEY AND TERRAIN ANALYSES IDENTIFY SIMILAR PRIORITY SITES FOR CONSERVATION?

Authors: Tomer, Mark; James, David

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2004
Publication Date: 11/1/2004
Citation: Tomer, M.D., James, D.E. 2004. Do soil survey and terrain analyses identify similar priority sites for conservation?. Soil Science Society of America Journal. 68:1905-1915.

Interpretive Summary: The targeting of conservation practices to sites where the greatest environmental benefits can be realized will optimize returns from the public's investment in agricultural conservation. Analyses of digital elevation data offer a way to precisely target conservation efforts. However soil survey is the traditional basis for conservation planning. This study evaluated the correspondence between soil survey information and data obtained from terrain analyses in two Iowa (West Nishnabotna and South Fork) watersheds. Major resource concerns are soil wetness in the South Fork's glacial terrain, and soil erosion in the West Nishnabotna's loess hills. Results showed targeting of conservation practices using terrain analysis can be consistent with soil survey information, but to a degree that varies with terrain and resource concern. For example, the largest 20% of terrain wetness index (W) values were about 80% hydric soils in the South Fork, and the largest 20% of terrain erosion index (E) values were about 80% HEL in the West Nishnabotna. But similar statements on E and HEL in the South Fork, and W and hydric soils in the West Nishnabotna, applied to few cells with <70% accuracy. Therefore, while terrain analyses can be a viable tool to supplement soil survey information and target conservation practices, this targeting will need to be put in context with local soil information for each resource problem being addressed. These results are important to conservation professionals, who in the future may increasingly apply results of terrain analysis to target conservation planning. Targeting criteria will need to be related to soils information if conservation planners are to apply these new methods with confidence. This study's results can also impact land managers by helping them understand new approaches to target conservation planning.

Technical Abstract: Terrain analyses may help target conservation practices, but soil survey is the traditional basis for conservation planning. This study's objective was to identify correspondence between terrain and soil-survey attributes. Iowa's South Fork (78000 ha) and West Nishnabotna (64000 ha) watersheds provided example datasets. Major resource concerns are soil wetness in the South Fork's glacial terrain, and soil erosion in the West Nishnabotna's loess hills. Slope, contributing area, curvature, and indices for wetness (W) and erosion (E), calculated from National Elevation Database data, were each divided into two groups according to erodible land (HEL), hydric-soil, drainage-class, topsoil-thickness, clay, and organic-matter-content attributes. All groupings had different means (p < 0.001), but proportions of captured variance ranged from <0.1 to 22%. 'Critical' values of slope and W segregated hydric, drainage, and topsoil-thickness groups with 66-74% accuracy in both watersheds, and slope and E segregated HEL groupings with 71-76% accuracy. Finer spatial detail in the terrain data appeared useful in dissected terrain, but artificial in near-level terrain. The largest 20% of W values were about 80% hydric soils in the South Fork, and the largest 20% of E values were about 80% HEL in the West Nishnabotna. But similar statements on E and HEL in the South Fork, and W and hydric soils in the West Nishnabotna, applied to few cells (<2%) with <70% accuracy. This indicates that targeting of conservation priorities using terrain analysis can be consistent with soil survey information, but to a degree that varies with terrain and resource concern.