The Bio History of a Fragipan Soil

[shearwater]

A fragipan soil is one which has large prisms located beneath the soil surface anywhere from 18 to 30 inches or more. The peds are characterized by a very dense soil material that fractures with strong pressure from the fingers, forming a sort of pop when they break. Fragipans develop in acid soil conditions of grasslan and the grass is thought to have made possible their formation. Grass has within its leaves silica particles called phytoliths. The theory goes that successive years of grass foliage lays down successive layers of this silica which is deposited on the soil surface and is dissolved by the water and acidity associated with decomposition. As the silica is liquified, it moves down the soil by gravity and recrystalizes in the lower depths. This crystalization cements soil particles to form very hard prisms which have a definite shape. Fragipan soils are impermeable to water and the soil water has to go around the prisms as is passes through the soil. So grass mines silica from the soil which is formed into phytoliths, deposits phytoliths on the soil surface where they are subsequently redissolved and leached back down into the soil where they recrystalizes in definite patterns.

[mudruncyndi]

Is this the same as the soil in and around Phoenix that the anasazi indians used to build with?