(or Hardpan) -- a hard impervious layer typically made from the downward translocation of clays in soil profiles. Water movement vertically across such a barrier is limited.
a dense and brittle pan, or layer, or soils. Its hardness results mainly from extreme density or compactness rather than from high clay content. The material may be dense enough to restrict root, nutrient, and water penetration.
A naturally occurring subsurface horizon that is low in organic matter, has a high bulk density, is slowly or very slowly permeable to water, is mottled and traversed by vertical or reticulate grey veins. It is hard when dry but exhibits a certain brittleness when moist; a common feature of New Zealand yellow-grey earths.
Brittle subsurface restricting soil horizon, usually loamy textured and weakly cemented.
A loamy, brittle subsurface horizon low in porosity and content of organic matter and low or moderate in clay but high in silt or very fine sand A fragipan appears cemented and restricts roots When dry, it is hard or very hard and has a higher bulk density than the horizon or horizons above. When moist, it tends to rupture suddenly under pressure rather than to deform slowly.