Agriculture Reference
In-Depth Information
ages, sizes, and morphologies, with perhaps a few coniferous trees and some grass species growing
within a delineation of deciduous forests on a vegetative map.
Maps are representations of the spatial distribution of classiÝed objects identiÝed at a reduced
scale. Soil maps are of many scales and are therefore best served by a classiÝcation system that
provides aggregation of the objects mapped in several levels of generalizationÐthis is one obvious
function of a hierarchical system of classiÝcation. The philosophies that guide the structure of
hierarchical systems for classifying objects subject to spatial mapping are in large part determined
by the mapping experience of the people constructing the classiÝcation system.
Comparisons among all soil classiÝcation systems are not possible, but one example illustrates
philosophies guided by a desire to reÞect soil properties vs. a desire to accommodate pragmatic
soil mapping concerns. All soil classiÝcation systems recognize poorly drained soils and well-
drained soils as distinct entities. Most soil scientists will agree that there are major differences in
composition and function associated with drainage characteristics. Most humid areas of the world
have a mosaic of well-drained and poorly drained soils spatially related to landscape features.
Hierarchical systems driven by a philosophy that identiÝes major contrasting soil properties have
poorly drained soils identiÝed at a high categorical level. Systems driven by experience with detailed
soil mapping at rather large scales tend to recognize poor drainage in subordinate categories, and
use higher hierarchical categories to identify soil properties spatially related to parent material or
broad physiographic regions, rather than local topography. This latter arrangement is compatible
for both small-scale maps that use taxonomic units of the higher categories for soil identiÝcation
and large-scale detailed maps that are able to delineate spatially intricate landscape positions and
use the taxonomic units of the lower, more detailed, categories to identify mapping units.
UTILITARIAN EXPECTATIONS OF SOIL CLASSIFICATION
Human need for soil information takes many forms. Each person can prioritize the following
needs, and perhaps others, that are expected of soil classiÝcation. Individual needs for information
shape individual philosophies of what a classiÝcation should entail.
¤
Analytical needs: Analytical need-based philosophy of classiÝcation seeks to accommodate the
needs of scientists as they seek fuller understanding of soil. A sample of soil material is a discrete
entity, but not a soil. Information obtained from the analysis of a soil sample contributes to our
knowledge of soil only if the location of that sample can be identiÝed both within an individual
soil and among all soils. Soil is a basic reagent for all land use. Quantitative transfer of technology
and research results to other sites requires that basic soil components be identiÝed with the same
rigor as the purity and normality of reagents are identiÝed in chemical experiments.
¤
Political needs: The philosophy of politically-based classiÝcation identiÝes projected response to
policy initiatives. Soil is a natural resource claimed by all political entities. Expenditures from
governmental coffers for soil-related technologies need to be directed to soils in which policy-
directed technology is applicable. The ability of soil scientists to correctly guide political decisions
has a pragmatic impact on Ýnancial support, and thus the sustainability of classiÝcation. Govern-
mental priorities arise, then wane. For example, assistance for installation of drainage systems in
Ñwet landsÒ was a goal of U.S. government policy in the 1950s, while preservation of Ñwet landsÒ
became the policy in the 1990s. Concerns for erosion control led to the land capability classiÝcation
system that guided the expenditure of funds for terraces, strip crops, and other soil conservation
practices to soils where erosion could be reduced, and avoided soils where such practices were of
little or no value. Political needs often require that classiÝcations identify soil and land subject to
speciÝc laws and regulations. Regulatory requirements are of all spatial scales. Some are site-
speciÝc and require identiÝcation of soil properties within pedons, i.e., elemental concentrations
in speciÝc horizons or depths. Land use regulations often relate to transient soil conditions, such
as saturation and Þooding. In the absence of statistically signiÝcant long-term observations of
sporadic events, pedogenic features are frequently used as evidence.
