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Soils
Introduction | Soil Formation | Parent Material | Physical Properties | Chemical Properties | Soil Profiles | Capability Classification | Soil Quality | Soil Survey
Chemical Properties of Soils
Chemical properties of soils affect nutrient availability to plants and soil acidity. Eighteen elements have been shown to be essential to the growth of plants. Some are considered macronutrients because they are used in relatively large amounts. Others are considered micronutrients because they are used in relatively small amounts. The macronutrients are carbon, hydrogen, and oxygen, which come from air and water. Nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur come mostly from soil constituents. To maintain healthy, productive soils, these nutrients may need to be added to the soil for optimum plant growth. Nitrogen, phosphorus, and potassium are normally applied to soil in most standard fertilizers. Calcium and magnesium are applied to soil in liming products. The burning of fossil fuels adds sulfur and nitrogen to the air, so they come back to the Earth with precipitation. Organic matter helps to hold these nutrients in the soil and releases them slowly.
One very important chemical property of soils is acidity. Acidity is usually evaluated by pH. Low pH values mean high soil acidity, while high pH values mean low soil acidity. Most plants grow best with pH values between 5.0 and 7.0.
Wetlands and Hydric Soils
Often called "nurseries of life," wetlands provide habitat for thousands of species of aquatic and terrestrial plants and animals. Although wetlands are best known for being a home to water lilies, turtles, frogs, snakes, alligators, and crocodiles, they also provide important habitat for waterfowl, fish, and mammals. Migrating birds use wetlands to rest and feed during their cross-continental journeys and as nesting sites when they are at home. As a result, wetland loss has a serious impact on these species. Habitat degradation since the 1970s has been a leading cause of species extinction.
Wetlands do more than provide habitat for plants and animals in the watershed. When rivers overflow, wetlands help to absorb and slow floodwaters. This ability to control floods can alleviate property damage and loss and can even save lives. Wetlands also absorb excess nutrients, sediment, and other pollutants before they reach rivers, lakes, and other water bodies. They are great spots for fishing, canoeing, hiking, and birdwatching, and they make wonderful outdoor classrooms for people of all ages.
Wetlands are identified by the presence of hydrophytic vegetation, water tables at or above the surface, and hydric soils. Hydric soil is a soil that formed under conditions of saturation, flooding, or ponding long enough during the growing season to develop anaerobic conditions in the upper part. The concept of hydric soils includes soils developed under sufficiently wet conditions to support the growth and regeneration of hydrophytic vegetation. Soils that are sufficiently wet because of artificial measures are included in the concept of hydric soils. Also, soils in which the hydrology has been artificially modified are hydric if the soil, in an unaltered state, was hydric. Some series, designated as hydric, have phases that are not hydric depending on water table, flooding, and ponding characteristics. Hydric soils may be organic or mineral. The mineral soils usually have very dark surfaces and/or gleyed (gray) horizons at or near the soil surface.
Additional information on wetlands and hydric soils can be found at
http://soils.usda.gov/use/hydric/intro.html and http://www.epa.gov/owow/wetlands/.
Introduction | Soil Formation | Parent Material | Physical Properties | Chemical Properties | Soil Profiles | Capability Classification | Soil Quality | Soil Survey
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