hardpan

A dense, compacted, nearly impervious layer of soil or clay found beneath the surface — so hard that roots cannot penetrate it and water cannot drain through it. Hardpan forms naturally through the cementation of minerals leached downward, or artificially through repeated mechanical compaction (tractor traffic, livestock trampling). A hardpan layer can turn productive land into a shallow basin that floods in rain and bakes in sun. Breaking a hardpan — with a subsoil plow, a keyline pattern, or deep-rooted plants — is one of the most consequential acts in land rehabilitation.