Soil Orders That Do Not Occur In Mississippi

Gelisols are soils of very cold climates that contain permafrost within 2 meters of the surface. These soils are limited geographically to the high-latitude polar regions and localized areas at high mountain elevations. Gelisols are estimated to occupy ~8.6% of the Earth's ice-free land area and ~8.7% of the US. Low soil temperatures cause soil-forming processe such as decomposition of organic materials to proceed very slowly. As a result, Gelisols store large quantities of organic carbon. The carbon contents of these soils are surpassed only by the histosols of swamp and marsh ecosystems. The frozen condition of gelisol landscapes also makes them sensitive to human activities. For this reason, there is great concern among ecologists and environmentalists, regarding recent government proposals to drill for petroleum in the Alaskan National Wildlife Refuge (ANWR).

Andisols are soils that have formed in volcanic ash or other volcanic ejecta. These soils differ from those of other orders in that they typically are dominated by glass and poorly crystalline colloidal materials such as allophane, imogolite, and ferrihydrite (andic properties). As a result, Andisols possess many unique chemical and physical properties that include high water-holding capacity and the ability to 'fix' (and make unavailable to plants) large quantities of phosphorus. Globally, Andisols only account for ~0.7% of the ice-free land area. They occupy ~1.7% of the US land area, including some very productive forests in the Pacific Northwest region. Mississippi once had active volcanoes and andisols might have developed here millions of years ago.

Oxisols are very highly weathered soils that are found primarily in the intertropical regions of the world. These soils contain few weatherable minerals and are often rich in Fe and Al oxide minerals. Oxisosl occupy ~7.5% of the global ice-free land area. In the US, they only occupy ~0.02% of the land area and are restricted in the U.S. to Hawaii and Puerto Rico. Although most Oxisols have extremely low native fertility, they can be extremely productive soils with inputs of lime and fertilizers.

Aridisols are CaCO3-containing soils of arid regions that exhibit at least some subsurface horizon development. They are characterized by being dry most of the year. Aridisols contain subsurface horizons in which clays, calcium carbonate, silica, salts, and/or gypsum have accumulated. Aridisols occupy ~12.0% of the Earth's ice-free land area and ~8.3% of the US. Aridisols are used mainly for range, wildlife, and recreation. Because of the dry climate in which they are found, they are not used for agricultural production unless irrigation water is available.