Soils

photo of nice lawn Soil is the unifying factor in Mississippi crop production. Understanding the fundamental properties of soils proceeds to better appreciation of soil fertility and fertilization, as well as soil management and conservation.

Integrating nutrient management, soil management, and conservation leads to considering soil quality or health. Simply put, soil quality is the ability of a particular soil to function as desired. Some functions include crop production, water control, or structure support.

What exactly is soil? There are many, many definitions. Specific ones depend on the viewpoint of the user. Some stakeholders consider soil to the living, breathing substance near the earth's surface which fosters life on all scales. Others consider it to be the aggravating skim on the earth's surface.

The study of soil is not the study of dirt. Dirt does not have life sustaining properties. Greenhouse media is not soil either. It does not have the unique three-dimensional characteristics that can only evolve as a function of place, time, and the environment.

More information on soil properties and formation are available on the Master Gardener reference manual links below.

Soil Taxonomy System

Someone coming into soils may think they are learning a foreign language. Soil folks do use specific terminology in discussing soils in a wholistic sense. Soil classification and nomenclature has been a challenge for centuries. Currently most of the world uses a system developed in the United States. An Alfisol in South America can be assumed to have similar characteristics to an Alfisol in Carroll County, Mississippi.

In the U.S. Taxonomy, soil properties are used to name them. Most agriculturalists are familar with series names, however series is only the final step of the system. The hoped-for strength of the system is a complete soil-name to convey lots of information in a relatively brief phrase.

The following is adapted from materials obtained from Professor Ed Nater. It contains some technical terms (argillic?) but is candid in discussing the strengths and weaknesses of the system.

Order: The broadest category in the system. Distinctions between orders are based largely on horizon morphology, with (unfortunately in some cases) soil genesis as an underlying factor. In general, each order is presumed to contain soils whose common properties suggest similar genesis. There are 12 orders in the taxonomy, but the key hasn't been updated to include the 12th yet. Eight of the 12 have been identified in Mississippi. More information on 11 of the orders is linked below.
Suborder: The suborders are subdivisions of the order based on factors such as wetness, climate (temperature and moisture), mode of deposition, texture, or diagnostic horizons. The number of suborders varies from four to seven within orders.
Great Group: Diagnostic horizons are often used to differentiate great groups within a suborder. For example, the presence or absence of an argillic horizon might distinguish one great group from another. (Argillic horizons are layers with observable clay accumulation in the soil profile. There are many soils in Mississippi containing argillics.)
Subgroup: The subgroups are subdivisions of the great groups. The typical, or central, concept of the great group makes one subgroup (Typic). Often, other subgroups are intergrades between the current great group and the central concepts of other great groups (i.e., mollic subgroups of Alfisols).
Family: The family category allows the grouping of members of a subgroup by such things as common texture, mineralogy, pH, soil temperature, coarse fragment content, or soil depth. This level of the system is often the most useful one for interpretations because it is the most descriptive.
Series: Soil series represents a collection of soils essentially uniform in most differentiating characteristics and the arrangement of horizons. This is level most often identified by farmers and the NRCS. Names are usually based on towns near where the soil was first identifed. There are about 700 named soils in Mississippi. Common series in the Mississippi Delta are Alligator, Sharkey, Dundee, Dobbs, and Forestdale. Prentiss, Ruston, Grenada, Memphis, Oktibbeha, and Smithdale are found in the hill portions of the state.