Soil Classifications
Entisols
Recent undeveloped soils; lack distinct horizons; poor agricultural soils, though those formed by river silt deposits can be fertile; formed from: Active slopes, alluvium filled floodplains, tundra, tidal mudflats, dune sands, erg deserts, and glacial plains
Andisols
Form in areas of High Volcanic Activity; derived from volcanic glass and ash; soil horizons frequently buried by ejecta from eruptions; Fertile from the Mineral Replenishment of Volcano
Histosols
Form where there's a large accumulation of Organic matter; can form in the beds of former lakes or other depressions which form bogs and peat; These are the materials that form Coal and other Fossil Fuels after compression over a long time
Gelisols
Found in peri-glacial landscapes; often are frozen (temp <32F); Most of organic matrial that grows here forms during short warm season and forms Tundra; Has Permafrost
Mollisols
Grassland Soils; good for agriculture (US plains/prairie); Dark and Thick Organic Layer; Soft even when dry and are very crumbly (dustbowl); May also go through calcification (Ca/MgCO3 layer) in the B and C Horizons
Vertisols
Heavy clay concentrations that expand with water and shrink when dry forming vertical cracks (>30% of soil must be these kinds of clays); Tend to form in subtropical and tropical areas with variable moisture and moderate to high temperatures not ideal for agriculture, but suitable
Ultisols
Highly weathered forest soils (southern US) derived from further weathered Alfisols; have more pronounced leaching making them redder, this reduces fertility (tobacco and cotton yields diminish; peanuts restore nitrogen)
Aridisols
Largest order of soils; occurs in arid regions (Deserts) [occupy 19% Earth's surface]; Have pale light layer near surface; soil horizons often small due to lack of water; Irrigate lands: salinization and water logging can be issues (aridisols are poorly drained/flash floods)
Alfisols
Moderately weathered forests soils; most widespread of the soil orders (equator-high latitudes); need application of lime in agriculture to reduce acidity; Sub-soil categories: Udalfs- humid and hot climates, Xeralfs-moist winter, dry summer characteristic of Mediterranean climates; good for nut crops, subtropical fruits, grapes, olives, artichokes, almonds, ands figs
Spodosols
Soils found in Northern Coniferous forests (North and East of Alfisols); Semi-humid mild summer climates; no comparable Southern Hemisphere counterpart; Sandy parent materials, shaded by forests of spruce, firn, and pine; lack humus and clay in A horizon; pine detritus on ground makes for sightly acidic soil and helps to concentrate clay and leached organic material in B horizon; lime helps agriculture, These soils are typically Gray
Oxisols
Soils located in the tropics, or equatorial latitudes; They're among the most mature soils on Earth and are characterized by extensive leaching due to abundant moisture; as a result these soils don't have distinct horizons, they do have distinct horizon of iron an aluminum oxides; Are themselves poor in fertility, but organic material above is able to recycle nutrients; May also form ironstone hardpan: clay material from leaching process (laterization), used for bricks.
Inceptisols
Weakly developed soils; high fertility (young formation but older than Entisols); found in moist soil regimes, where glacial activity has occurred (10,000 yrs end of Ice Age)
