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Desert soils form in areas where the demand for water by the atmosphere (evaporation) and plants (transpiration) is much greater than precipitation. Deserts cover 20 to 33% of the Earth’s land surface, and can be found in the tropics, at the poles, and in between.
Deserts are defined as being very dry. Not all of them are hot, or sandy. The antarctic continent is a dry, polar desert. At the south pole, it doesn't snow very often, though, blowing snow can accumulate up to 20 cm. Even though moisture levels are really low, deserts are prone to flash flooding when they recieve rain. This is what causes all of the interesting and colorful rock formations. The lack of soil moisture keeps minerals from leaching out of the soils, and can even create cement like horizons near the soil surface.
Most desert soils are called Aridisols (dry soil). However, in really dry regions of the Sahara and Australian outback, the soil orders are called Entisols. Entisols are new soils, like sand dunes, which are too dry for any major soil horizon development. They also occur in floodplains after a spring flood, which is why they can occur in the desert.
The desert may look dry, but it still contains a lot of living organisms. This includes a living, biological crust, whcih is formed by algae, moss, and lichens in a group. Aridisols are very fertile, however, often don't have the rainfall to sustain life. When it rains, dormant seeds wake up and form desert blooms. The permanent vegetation (like cacti and shrubs) is very well adapted to living without moisture for long periods of time.
Relief and Parent materials in the desert are highly variable, depending on where the desert is. Some of the desert rock features that crumble and form entisols at the base are very steep, as are some of the dunes. Other features, like the Racetrack Playa in death valley are flat because they are old lakebeds. The soils come in all different textures, and can be deposited by wind or water.
Some deserts are very old, and because of desertification, others are remarkably new. Desertification is the spreading of the deserts into areas that were not previously desert, is caused by several different things. See the desertification page for more information.
The deserts are very fertile, which means that, if provided with water, they can grow a lot of food. This can by done by providing water with irrigation technology. The Central Valley in California produces 250 types of fruits and vegetables, and does so with river water, aquifers, and streams.
Sometimes irrigation water can be used up, so it is important to consider conservation options. Irrigating in a dry climate, especially flood irrigation can cause the water to evaporate very quickly. When that happens, the salts are left behind on the soil surface. This build up of salt is called salinization. Since few crops can deal with high salt levels, the soils become too salty to grow anything. For more information, visit the salinization page.
Desert soils (Aridisols) occupy about 12% of the Earth’s ice-free land surface, and 8% of the United States land area, all in the western states: Texas, New Mexico, Colorado, Wyoming, Montana, Arizona, Utah, Nevada, Idaho, California, Oregon, and Washington. However, deserts themselves occupy a total of 33% of the worlds land area, with Antartica occupying another 14%.
For more information on the desert, including downloadable PowerPoints, assessment questions, and educational links, please visit the SCOOP! Teachers Guide.
UC-Berkeley Website. More information on the desert biomes, including plants, and detailed climate breakdowns for the four major desert types
Kids do Ecology - University of California at Santa Barbara
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