Psamment

In USDA soil taxonomy, a psamment is defined as an entisol which consists basically of unconsolidated sand deposits, often found in shifting sand dunes but also in areas of very coarse-textured parent material subject to millions of years of weathering. This latter case is characteristic of the Guiana Highlands of northern South America. A psamment has no distinct soil horizons, and must consist entirely of material of loamy sand or coarser in texture. In the FAO soil classification, psamments are known as arenosols.

Psamments cover 3.4% of the global land mass. They occur throughout the world, being especially abundant in the deserts of Africa and Australia and on the ancient landforms of eastern South America. Areas dominated by psamments also occur in other humid regions, notably in Florida and Nebraska (the Sand Hills).

Psamments typically have very low water-holding capacities because the sand in the soil is not graded so that sands of varying coarseness are constantly mixed right through the soil. Because most sands are highly siliceous, psamments are also extremely low in all essential nutrients, most especially phosphorus and are highly acidic in all except very arid climates. Psamments formed as a result of glacial erosion (common in northern Europe) are typically of rather higher native fertility because of their youth, but are still much less fertile than most soils in the regions they are located in.

The vegetation on psamments varies enormously owing to the variety of climates, but in many cases is remarkably well-adapted to the climate, as with the Fynbos of the Cape region in South Africa—famous for its remarkable biodiversity and the equally species-rich Kwongan of southwestern Western Australia. The campinas and kerangas are healthy forests typical of psamments in South America and Borneo.

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