Chapter 14: Soil Family and Series (Continued)

Family Criteria and Guidelines for Organic Soils

Family criteria apply to the organic control section as defined in Chapter 2.

Nomenclature for Soil Families

The technical soil family name is descriptive and consists of the subgroup name followed by several adjectives designating the mineral or organic family classes and subclasses, and should be terminated by the term family. The classes and subclasses are listed in the following order:

• Mineral soils; particle size, mineralogy, depth, reaction, calcareousness, soil temperature, and soil moisture regime.
• Organic soils; characteristics of surface tier, reaction, soil temperature, soil moisture regime, particle-size of terric layer, limnic material, and depth.

Some of the modifiers are not necessary for some subgroups; for example, the reaction class should not be indicated for Alkaline Solonetzs. Some examples of family names are

• Orthic Humo-Ferric Podzol, coarse-loamy, mixed, acid, cool, perhumid family.
• Orthic Eutric Brunisol, coarse-silty over sandy, mixed, shallow, strongly calcareous, cold, humid family.
• Terric Mesisol, humic, dysic, cool, aquic, loamy-skeletal family.
• Limnic Humisol, humic, euic, mild, aquic, coprogenous family.

A family thus described is a taxonomic entity within which from one to a large number of series may be established. Like the series, its suitability as a basis for naming pure or complex mapping units varies from region to region and according to the scale of mapping.

In some instances it is useful to indicate phases of families (see Chapter 15, Soil Phase). This is done by adding, after the term family, the appropriate phase terms and "phase." An example is

• Orthic Humo-Ferric Podzol, coarse-loamy, mixed, acid, cool, perhumid family; peaty, level phase.

For convenience and brevity the name of a common series may be used to designate a family. For example, it is acceptable to refer to "Breton family" to indicate the Orthic Gray Luvisol, fine-loamy, mixed, neutral, cold, subhumid family.

Soil Series

The concept of the soil series has changed greatly since the early 1900s when a series was somewhat analogous to a geological formation. Now the series is a category in the system of soil taxonomy in the same way that order, great group, subgroup, and family are categories. A soil series is a conceptual class that has, or should have, defined limits in the same way as a great group. The link between the conceptual entity, soil series, and real bodies of soil is the pedon. Any pedon may be classified as a unique soil series, but series have been named for only a very small proportion of the kinds of pedons that occur.

Soil series are subdivisions of soil families based upon relatively detailed properties of the pedon within the depth of the control section. The range of variability of the differentiating characteristics is narrower for the series than for the family. Series cannot transgress soil climatic and particle-size classes, or other boundaries recognized in family separations. The significance of differences in the properties of the different kinds of pedons that fall within a soil family depends on how these properties combine. No specific property, or group of properties, has been assigned limits and been used consistently from family to family and within families to define series. Each potential soil series is treated as an individual case and the decision on whether or not it should be recognized as a separate taxon involves a judgment based on the following guidelines:

1. The properties that distinguish a particular series from other series must be sufficiently recognizable that qualified pedologists can identify the series consistently.
2. The properties used to differentiate series must be within the control section (see 4 and 5 below).
3. Soils of a series must occupy at least a few hundred hectares. Establishing a series to classify a few pedons that occupy a few hectares is not justified even if the pedons have unique properties.
4. Soil series within families of mineral soils are usually differentiated based on the following properties:
   1. color, including mottling;
   2. texture;
   3. structure;
   4. consistence;
   5. thickness, relative arrangement of horizons, and degree of expression of horizons and of the solum;
   6. abundance and size of coarse fragments;
   7. depth to a lithic contact, permafrost, or contrasting material to a finer degree than used in higher categories;
   8. depth to, and concentration of free carbonates;
   9. depth to, and concentration of soluble salts;
   10. reaction (pH);
   11. lithology.
5. Soil series within families of Organic soils may be differentiated based on the following properties:
   1. material composition—botanical origin of fibers and nature of terric layer, if any;
   2. thickness, amount of decomposition and relative arrangement of layers;
   3. abundance of woody material—logs and stumps;
   4. calcareousness;
   5. bulk density;
   6. mineral content of organic material;
   7. soil development in the terric layer;
   8. mineralogy of terric or cumulic layers;
   9. texture of terric or cumulic layers;
   10. reaction (pH).

Few series of Organic soils have been established and it is likely that other series criteria will emerge.

Pedons classified as a given soil series have a similar number and arrangement of horizons whose color, texture, structure, consistence, thickness, reaction, or some combination of these properties are within a defined range. In the case of soils without genetic horizons, the above statement applies to the C horizons to the depth of the control section.

The concept of the soil series has been refined progressively in Canada throughout the last half century. Many"series" established 30 or more years ago might include pedons that belong to several subgroups or families today. Years ago soil taxonomy was focused on the series and the great group; much less attention was given to other categories. Series were differentiated without reference to family criteria, which were not developed until recently. Thus many of the "series" used today still include, to a degree, the attributes of the more generalized series of several years ago. In the process of establishing new series and refining old series today, the pedologist should work downward in soil taxonomy considering the differentiation of soil properties at the order, great group, subgroup, and family levels before subdividing the family into series. Taxonomy will probably not be extended to the series level in many medium- to small-scale soil surveys. For more detailed work, the series is a category of paramount importance because it is the most specific level in soil taxonomy and the one used for most interpretations. Sound judgments, based upon the guidelines stated, on the part of soil mappers and correlators are essential in decisions on establishing series. The definition of a series implies a statement of the limits of its properties.

Source: The Canadian System of Soil Classification (Third Edition)