WHAT ARE SOIL SERIES?
– They constitute the most detailed hierarchical category in a soil
classification system.
– They are practically independent from the classification system to
which they refer (Boulaine, 1980)
– Each soil series represents a specific soil class with a unique set of physical,
chemical and mineralogical characteristics It is the most
homogenous category in taxonomy.
WHAT ARE SOIL SERIES FOR?
They constitute an essential vehicle for transferring soil information and knowledge from one place (where it was obtained) to another (where there are similar soils).
QWHICH SOILS FORM PART OF A SOIL SERIES?
The soils of a particular series
– have similar observable properties;
– have similar reactions with regard to their use and management;
– have similar horizons in their layout and characteristics;
– are homogenous and have developed from a particular original material
– exhibit properties that vary within a narrowly defined range. The surface horizon
and soil features such as slope, stoniness, the extent of erosion and
topographical position may all vary, but these features are associated
with significant differences in the classes and the layout of the
horizons.
HOW CAN WE DIFFERENTIATE BETWEEN SOIL SERIES?
The following criteria are generally used to differentiate between soil series, with more specific details being established for each country and geographical region:
– classes, thicknesses and the layout of the soil horizons;
– soil structure, colour, texture, reaction, consistency, calcium carbonate
and soluble salt content, organic matter, coarse elements and
mineral composition.
Significant differences in any of these properties may serve as the basis for identifying different series. It is very rare for differences to be based on only one of these characteristics because due to their relationship with soil formation processes more than one of them tends to vary at a given time
A series is perfectly characterized by
– its position in the landscape, slope and material of origin;
– eits morphological aspect: its sequence of horizons, structure, colour, coarse
elements, and depth, etc.;
– eits functional aspect: its temperature regime, drainage class, permeability,
etc.;
– its mineralogy: the nature of its clay and other minerals;
– its analytical aspect: its particle size and distribution,
reaction, cation exchange capacity (CIC), iron
content, organic carbon content, calcium carbonate, etc.;
– the permitted range of variation for each of its characteristics.
HOW ARE SOIL SERIES DENOMINATED?
A soil series normally bears the name of the area where it was first recognized, which is a place at which the soil in question is well represented in the surrounding area.
Soil series should therefore be described for each territory and should have locally appropriate names. At meetings and in scientific works, it is habitual to use higher hierarchical levels.
CORRELATION OF SOILS
Each series should be described in a detailed way, following a standardised format applied by the different survey teams. This definition is dynamic, because it can be improved with time; as knowledge of the soil increases, it is possible to improve the definition of a given series.
In order to avoid duplications, the Department of Agriculture of the USA (USDA) created the figure of soils correlator, with three important functions:
– to check that each candidate for recognition as a new series really is such and
that it has been described according to the established standard
– to keep a single, constantly up-dated, soil series record;
– to check that the limits established for map units coincide with those of earlier
maps.
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