Marginality Principle - Principles of Sustainable Soil Management in Agroecosystems - page 22

TABLE 2.1
Land Capability Classification and Definitions

Classiication Definitions

1 Soils have slight limitations that restrict their use.

2 Soils have moderate limitations that restrict the choice of plants or that require

moderate conservation practices.

3 Soils have severe limitations that restrict the choice of plants or that require special

conservation practices, or both.

4 Soils have very severe limitations that restrict the choice of plants or that require very

careful management, or both.

5 Soils are subject to little or no erosion but have other limitations, impractical to remove,

that restrict their use mainly to pasture, rangeland, forestland, or wildlife habitat.

6 Soils have severe limitations that make them generally unsuitable for cultivation and

that restrict their use mainly to pasture, rangeland, forestland, or wildlife habitat.

7 Soils have very severe limitations that make them unsuitable for cultivation and that

restrict their use mainly to pasture, rangeland, forestland, or wildlife habitat.

8 Soils and miscellaneous areas have limitations that preclude commercial plant

production and that restrict their use to recreational purposes, wildlife habitat,
watershed, or esthetic purposes.

Source: National Soil Survey Handbook, 2012. Natural Resources Conservation Service, USDA,
Washington, D.C., http://soils.usda.gov/technical/handbook .
Note: Subclasses exist to describe the main hazard for each capability classification and are denoted by
subscripts to the class, for example, erosion (e), water (w), shallow or droughty (s), and very cold
or very dry (c).

They are generally considered unsuitable for cultivation and have pasture, woodland,
recreation, wildlife, and water supply uses. This capability classification system is
widely applied to agricultural landscapes and often leads to a devaluation of the eco-
system services different soil types may provide.
The characteristics of soils and their functional uses are not static but change over
time naturally and through anthropological activities. Soil formation occurs as a result
of time, parent material, climate, topography, and organisms all working together to cre-
ate the vast array of soils we have around the world (Jenny 1941). The time scale of soil
formation is hundreds and millions of years compared with the time scale of hours, days,
weeks, and years in which soil functions can be lost. It is of particular interest whether
soils have maintained their ability to perform their different functions. Soil ability to
perform valued functions has been defined by soil scientists as soil quality (Doran et
al. 1994; Doran and Parkin 1994). Two questions arise from scientific and nonscientific
land manager definitions of marginality and soil quality: (1) Which function of soil does
society give high priority value, and how does that affect definitions of marginality?
(2) How much of a deviation away from the optimal functioning of a soil is necessary for
the soil to be marginalized? For example, if we lose a 10% capability of producing a crop,
is that sufficient to consider the soil as marginal? If we suffer a loss of 0.5 cm of topsoil,
does that move a quality soil into a marginal category? If the soil water holding capacity