Marginality Principle - Principles of Sustainable Soil Management in Agroecosystems - page 21

FIGURE 2.2 Vertical distribution of soil layers from a Nashville-series soil. (From USDA-
NRCS. Available at soils.usda.gov/gallery/photos/profiles, accessed July 13, 2012.)
often accompanied by charts linking soil traits to particular functions to help landown-
ers, engineers and technical specialists, government officials, teachers, and developers
in land use investments, planning, and decision making.
The concept of marginality applied to soils has its origins in how humans value
the functions of soils and the different characteristics they provide. Although soils
have multifunctional capacities, some functions are valued above others. The soil's
ability to effectively and efficiently produce food and economic livelihoods under-
lies common valuations of soil quality and marginality. The US Department of
Agriculture (USDA) Natural Resources Conservation Service (NRCS) soil capabil-
ity classification system (Class 1-Class 8) uses the land's ability to grow crops as a
metric to evaluate soil suitability for particular uses with the definitions shown in
Table 2.1 . These capability classes are given relative to a specific purpose for which
the soil is being used, that is, capability classification will depend upon whether
the soil is being used for annual crops, perennial crops, forests, and so forth. This
method provides a measure of the suitability of the soil to perform its intended use,
and most often, these methods are related to agricultural uses. Class 1 is best suited
for growing a wide range of crops, and Class 8 is considered unsuitable for grow-
ing crops (Hamdar 1999). Classes 2 and 3 have moderate to severe limitations that
reduce the choice of plants that can be grown and require special conservation prac-
tices to assure crop productivity. Under this classification system, marginal lands are
those with severe limitations (Classes 4-8) and considerable reduction in the types
of vegetation that will grow and thus require careful management (Hamdar 1999).