Agriculture Reference
In-Depth Information
(Ivanova and Rozov, 1970). They distinguished 110 soil types in the Soviet Union in accordance
with climatic zones, drainage, and such soil characteristics as organic matter, base saturation, and
salinization. The second hierarchical level is subtype. Subtypes are divided on the base of subdom-
inant soil features (for example, calcareous or noncalcareous, saline or nonsaline chernozems). The
third level is genera, which is based on the genetically important speciÝcity of parent material,
groundwater, etc. The fourth level is species. Species is distinguished by quantitative criteria Ð
depth of humic or bleached horizons, humus content, percentage of salts. These reÝnements reÞect
the hierarchical approach and the quantiÝcation of the classiÝcation criteria, becoming the basis
for the ofÝcial soil classiÝcation system of the Soviet Union.
EVOLUTIONARY APPROACH TO SOIL CLASSIFICATION
Developments in the understanding of pedogenesis, as illustrated previously, were a dominant
factor contributing to the modiÝcations of the classiÝcation systems. The Ýrst classiÝcation system
that considered evolution of the soil as an important factor was proposed in 1932 by B.B. Polynov.
According to him pedogenesis is a stage in the process of formation of a weathering mantle. He
distinguished four trends of pedogenesis:
1.
Eluvial with downward movement of soil solutions
2.
Lacustrine-swampy-solonchakous with weak or upward movement of soil moisture
3.
Swamping and salinization
4.
Draining and leaching
Trends are divided into chemical or mineralogical groups (for example, alkaline and acid), and
groups are divided into types by the stages of development (for example, alkaline group is divided
into primitive-alkaline, pre-chernozemic and chernozemic types). The lower levels of PolynovÔs
systems are subtypes based on temperature; stages differentiated by quantitative parameters of the
leading process; forms differentiated by the development of soil proÝles; species differentiated by
the presence or absence of the laterally transported material; and variations differentiated by land
use. The total number of variants in PolynovÔs systems is 2800. So, this system was a major
deviation from existing systems but it considered only the mineral composition of the soil. Further,
it was considered to be too theoretical, and was ignored to some extent.
Another major development was introduced by Kovda in the 1960s. Perception of soils as
results of broad geochemical mass-energy exchange processes, interacting in time in accordance
with the evolution of landscapes, was the background for the world system elaborated from 1967
to 1975 by V.A. Kovda with his colleagues (Kovda et al., 1967). The Ýrst entry, or the upper
category, is presented by broad soil-geochemical formations differentiated by major trends of
weathering, types of humus, clay minerals, acid-base properties, and neoformations, supplemented
with characteristics of climate and vegetation. The second entry is Ñstadial groups of soils,Ò
corresponding to hypothetical evolution stages, from submerged sites to excessively drained ones.
The following stadial groups were proposed: hydroaccumulative, hydromorphic, mesohydromor-
phic, paleohydromorphic, proterohydromorphic, automorphic (including mountain soils), paleoau-
tomorphic. The number of stadial groups, as well as that of soil-geochemical formations, varied in
different versions of this system. Moreover, climatic zones or belts were introduced in the early
ones, and climatic facies (sections) in the Ýnal version.
Such theoretical considerations in soil classiÝcation were scientiÝcally interesting, but were
considered speculative to some extent, as they were not supported by data or experimentation. They
were considered to be based only on the authorÔs hypotheses, and many of the assumed processes
or trends were debatable. However, they reÞected a stage in the evolution of Soviet Soil Science
