Soils
Soils are an important component of the forest landscape. Soils perform several different functions in the forest landscape including habitat for soil organisms, recycling systems for nutrients and organic wastes, provisions of water supply and its purification, and as a medium for plant growth (Brady and Weil 1999). Different soil types perform these functions in different ways. Some soils may be better growing mediums while others provide better organism habitat. For example, sandy soil allows water and nutrients to flow through the soil, while clay soil creates an impenetrable soil surface. Clay soil is generally not a good soil for use as an engineering medium because of its tendency to shrink and swell based on the water content of the soil. Yet, chemicals and nutrients are not held by sandy soil in plant-available form as they are by a clay soil.
With that in mind, it is important to differentiate between soil types. Soils are classified into six different taxonomic categories including 1) order, 2) suborder, 3) great group, 4) subgroup, 5) family, and 6) series.
We will limit our discussion to the top level classification or soil orders. Soil orders are differentiated by the presence or absence of diagnostic horizons or features that reflect major courses of development. There are twelve different soil orders. Order names provide a characteristic of the soil and end in sols (from the Latin solum, soil). Temperature and moisture are the climatic factors that most frequently affect the soils in the area. It should be noted that since soil orders are the most general level of soil classification, variation of soil characteristics within orders is quite large and, therefore, should be used accordingly. The diagram to the right shows the typical temperature and moisture factors related to each soil order. The table below can serve as a key reference to identifying soil orders. It provides major diagnostic features for each order.
Eight of the twelve soil orders are present in the forests of the Southern United States. Orders in small amounts include Histosols, Entisols, Mollisols, and Spodosols. The prominent soil orders, listed in order of productive capacity, in the South include:
Photographs and distribution maps of dominant soil orders can be found on the Natural Resources Conservation website and at the University of Idaho website.
Soil surveys provide soil maps and interpretations needed in giving technical assistance to natural resource managers; in guiding decisions about soil selection, use, and management; and in planning research and disseminating the results of research. The surveys also are used in educational programs about soil use and conservation. County-level soil surveys can be found at the NRCS website. Additional assistance is available from USDA Service Centers. These centers are designed to be a single location where customers can access the services provided by the Farm Service Agency, Natural Resources Conservation Service, and the Rural Development agencies. Service centers for each state are shown on the USDA website. The site will provide the address of a USDA Service Center and other Agency offices serving your area along with information on how to contact them.
The conservation of forest soils is an important component of a sustainable bioenergy and bio-based products industry in the Southern United States. A more detailed discussion of forest soils and their role in the bioenergy and bio-based products value chain is contained in Soil Values in the Environmental Sustainability section.
Encyclopedia ID: p1353
