Fragipan Horizons: Definition, Properties, Genesis, and Influence on Soil Behavior

Abstract

Many Missouri forest soils exhibit fragipans, which influence soil productivity, ecosystem services and land management. Fragipan bearing soils tend to occur where loess thickness is moderate (1 to 2 meters) or where the soil profile exhibits evidence of mass wasting of weathered limestone residuum. Consensus is consolidating around the self-weight collapse of loess and residuum after repeated wetting and desiccation. The use of gravel as an indicator of parent material differences and its correlation with fragipan development is not perfectly aligned, thus although most fragipans do exhibit a bisequal soil profile, the placement of the lithologic discontinuity is difficult given mass wasting, eluviation-illuviation, side slopes, and other soil processes that contribute to increasing the bulk density and conferring strength. Fragipan genesis is evolving; however, research involving Ecosystem Site Descriptions are a fusion of a land parcel’s soil properties, vegetational community, hydrology, and climate to guide land management. Ecological Site Descriptions associated with fragipan bearing soils are necessary, especially when making land management decisions.