Soils comprise the upper surface of the Earth's crust and form the substrate for living matter in upland areas. Soils are a mixture of mineral matter, organic matter, and living biological organisms, and are formed through the erosion of rock and the breakdown of organic matter. Soil requires thousands of years to develop, but can be eroded quickly through wind or water erosion, along with human activities. For example, it is estimated that seventy five percent of the world's topsoil has been lost since the European discovery of the New World; a rate currently estimated at 300 tons a minute, worldwide.
Soils exhibit physical, chemical, and biological characteristics and soil types vary throughout geographic areas. Density, texture, color, water retention rate, and structure are some of the physical characteristics. Chemical characteristics include mineral composition, pH, and organic matter content. Biological characteristics include the organisms living within the soil, such as bacteria, fungi, insects, worms, and small animals.
Soils are important because they influence the type and abundance of vegetative species. "Fertile" soils can support naturally-occurring species, agricultural crops, and even the plants and flowers in your backyard. Soil also controls how much water infiltrates into the ground and how quickly. For example, certain plants prefer sandier soils that drain quickly, whereas other species prefer muddier soils that retain water longer. Therefore, the type of soil that occurs in an area determines the floral species and, in turn, the faunal species.
Soils can be anthropogenically altered in several ways. When soils are compacted, due to driving or construction activities, water cannot infiltrate into the soil as efficiently. Following precipitation events, standing water may appear or may run-off into surrounding low-lying areas. This can be problematic to nearby residential or commercial areas. Soil infiltration rates can also be altered through the addition of new, non-native soil types. The Florida state soil Myakka, for example, is typically found in flatwoods areas. This wet, sandy soil supports vegetation such as saw palmettos and longleaf and slash pines. The introduction of a muddier soil would not support the same vegetation and/or animal species.
Soil samples are collected and analyzed using hand-held or laboratory equipment for characteristics such as grain size, pH, organic matter composition, and nutrients.
Soil calculations vary depending on the particular characteristics being studied.