Fragipan soils of the eastern United States.

Publisher Summary This chapter presents an overview of the fragipan soil of the Eastern United States. Fragipans are subsoil horizons that are brittle and rigid when moist, that restrict root growth, and that transmit low-tension water more slowly than the overlying horizons. They occur in soils subjected to net downward water movement. Some fragipans have undergone strong eluviation, illuviation, or both. Others occur in soil materials that exhibit only the weak alteration of the parent material. Depth to the fragipan largely determines its influence on plant growth. Soils with shallow fragipans commonly have high water tables that may be a factor in restricting rooting depth. The importance of fragipans to the mechanical manipulation of soils is largely relatable to their slow transmission of low-tension water. In the Comprehensive Soil Classification System, fragipans are diagnostic at the great group level and they are recognized in that category in four soil orders. Fragipans unfavorably influence growth by restricting rooting, either through mechanical impedance or by creating saturated conditions.