National Soil Survey Committee

National Soil Survey Committee

Preliminary Report of Sub-Committee

On

Soil Classification

1949

Sub-Committee Personnel:

W. E. Bowser, University of Alberta

F.F. Morwick, Ontario Agricultural College

P.C. Stobbe (Chair), Central Experimental Farm

Introduction

The classification of soils generally and the creation of uniform system of classification in particular, are very complex problems largely because not enough facts are known about the soils. Nevertheless, as the soils are being studied and mapped, the data concerning the soils must be classified to permit systematic handling and orderly treatment.

Reports received from the different provinces show that there is considerable lack of uniformity in the classification of soils in the various provinces. In some provinces individual soils have been mapped as separate units without much attempt to group them into larger categories, while in other cases much stress has been laid on the grouping into larger categories according to certain relationships between different soils. Fortunately, the different soil units in all cases have been established and mapped on the basis of characteristics expressed in the soil itself, i.e. the soil profile. It is true that the sizes of the mapped units, such as series, etc., or the variability within the mapped units often vary from province to province, depending on the detail with which the soils have been mapped and the purpose for which a particular survey has been made. This fact, however, is not an insurmountable obstacle to an orderly classification of soils.

Soils may be classified on different bases, depending on the purpose of the groupings and the use for which it is desired. A national system of soil classification should be based on inherent soil characteristics which are common to a number of soils. Such soil characteristics are brought about by and associated with the various factors that control soil development. A national system of classification should be practical in order to take care of natural soil variations as they occur in the field. It also should provide room for any soil units which are at present not known.

In this report the sub-committee is submitting a tentative system of classification for consideration to a national committee. Such a general classification should in no way interfere with the rearrangement or regrouping of soils for local needs and it will provide an excellent means for the correlation of soils throughout the dominion. In drawing up this general outline the sub-committee has taken into consideration all the various reports received from the different members and ideas obtained by the chairman during visits to the field in the different provinces have been incorporated where possible. The sub-committee hopes that all the members will give this report careful study with regard to its adaptability to the various conditions. Any constructive criticism and suggestions for further improvements of the scheme will be greatly welcomed.

Suggested Tentative Classifications

The sub-committee would like to suggest that the Canadian soil be first all grouped or divided into three main regions according to their common morphological characteristics and according to the environmental factors under which the soil have developed. These are:

1. The tundra soils region

2. The woodland soils region: Grey wooded zone

Podzol zone

Grey-brown podzolic zone

Brown podzolic zone

Yellow-brown podzolic zone

3. The grassland soils region: Brown zone

Dark Brown zone

Black earth zone

This division is not based on vegetative cover alone and thus is not a botanical or vegetative classification as some would perhaps like to suggest, but is more associated with the characteristics of the soil itself. The soils of the grasslands region have developed under a grass cover and have characteristic profiles in which the organic matter is intimately mixed with the mineral fraction of the soil in the upper horizons, which usually have a layer of lime accumulation in the subsoil and have or tend to have a columnar or column-like structure. The woodland soils have developed under forest vegetation and the organic matter in these soils is usually concentrated on the surface of the soil, rather than intimately mixed with the upper horizons of the soil itself. The layer of lime accumulation is often, although not always, absent and the structure of the subsoil tends to be nutty or cloddy rather than columnar. The woodland soils generally show more signs of leaching and have a lower pH than the grassland soils. The grassland and woodland soils correspond generally to the so-called pedocals and pedalfers, respectively; however, those wooded soils which have a layer of lime accumulation present, partially due to excessive amounts of residual lime, would be classed with the woodland rather than with the grassland soils.

Although very little accurate information is available about the tundra soils it is tentatively suggested that the tundra region includes those soils with an ever-frozen subsoil. Due to the enormous extent of the forested area great soil variation must be expected fro the typical woodland soils to the tundra soils and it may be desirable, as information is accumulated, to establish a woodland-tundra transition region.

Soil Zones

The soils of the two better known regions, the grassland and woodland or forest soils can further be subdivided into soil zones. The soil zone at present is in practically all provinces the largest category of soils recorded. They are largely determined by soil characteristics which can conveniently be correlated with climate and vegetation over comparatively broad areas. In studying the various reports it appears that the interpretation of a soil zone may vary somewhat between some of the provinces. In some cases a soil zone is taken to represent a great soils group, for example, the podzols, the black earth ((thermosems), etc. The committee would suggest that a zone should be defined as a broad belt of soils in which the dominant normal soils correspond to the soils of a great soils group, such as podzols, black earth, etc. The dominant soil forming processes in a zone are towards the formation of a definite type of soil (podzol, black earth, etc.) but due to local conditions many soils may be formed in a soil zone which are not of the same type as the dominant soil. Thus, for example, a podzol zone may contain true podzols and a number of soils which are not or only slightly podzolized due to drainage conditions or parent material or both. Similarly the black soil zone will contain a large proportion of black earth soils and various wiesenbodens, saline and alkali soils and locally leached or podzolized soils. A soil zone, therefore, is a large complex in which different “types” of soils can be found. However, the dominant soil forming processes in a zone are toward the formation of a definite “type” (podzol, black earth, etc.) which tends to dominate in the respective zones.

In connection with the definition and delineation of the different soil zones much work needs to be done. Most of the men in different provinces have a fairly definite idea of what they mean by each zone and generally the ideas held in the different provinces coincide fairly closely. However, in the transition belts from zone to zone, personal factors in interpretation come into important play as the definitions are too loose to take the minor variations into account. This makes it often difficult to establish uninterrupted zonal lines across provinces even if the soil has been studied and mapped with great care. These difficulties can only be overcome by much closer contact between the surveyors of the different provinces and by a joint study of the different zonal variations that are permitted in the different provinces. This not only applies to zonal differences but also to individual mapping units in adjacent provinces. In other words, the members in one province should know more about what the adjacent provinces are doing and how they are doing it.

In some cases large areas of soils are uninvestigated and unsurveyed to date and no definite soil zone lines can be established in such areas until the facts about these soils are known. In other cases considerable information concerning the soils has been collected by surveys and other investigations and the zones have been fairly well established.

It is suggested that three main soil zones should be recognized in the grassland region, namely the brown, the dark brown and the black earth zones. It is also suggested that these zones should be defined in collaboration by the surveyors of the three Prairie Provinces and that the zonal lines should be checked along the borders by surveyors of the provinces concerned.

In the woodland region the soils have in most instances not been sufficiently studied to permit the establishment of zonal lines as closely as has been done in the grassland region. However, from information at hand it would seem that the following zones should be recognized:

1) The grey wooded zone

2) The podzol soil zone

3) The grey brown podzolic zone

4) The brown podzolic zone, and

5) The soil zone along the Pacific coast (yellow-brown podzolic?)

Although lack of information may at present not permit the exact definition and delineation of these zones, nevertheless, work done to date is sufficient to indicate that these zones exist and that the soils of the representative zones differ in their characteristics and can definitely be correlated with climatic and vegetative conditions. Every effort should be made by all provinces to define and delineate the soil zones clearly. It is possible that with more intensive study it may become desirable to establish one or two additional zones.

Sub-zones

Many of the soil zones are very extensive with considerable soil variations. Some of these variations are quite gradual and can be related to climatic and vegetative variations rather than to local changes in parent material and relief. In some cases these soil variations caused by minor climatic changes are accentuated by changes in parent material over extensive areas, over shadowing the smaller climatic variations. It is suggested that some of the larger soil variations within a zone which can be linked with small climatic changes and which may or may not be accompanied with changes in parent materials be recognized as sub-zones. Such variations have already been recognized in a number of provinces and have been designated as zones. Examples of such variations are the “Deep” and “Shallow” black zones or sub-zones in Alberta, the “Black- dark brown” transition zones, the “Black” and “Northern black” zones in Manitoba, and the “Degraded-black” of “Black –grey wooded” transition zones in the three prairie provinces. In a similar category would probably fall the “Rendzina” soils in Manitoba. I may become desirable to establish other similar sub-zones, such as, a greybrown transition of the brown podzolic zone and other sub-zones within the grey wooded zone, as these are being studied in more detail. Similar sub-zones would be of great assistance in separating some of the major variations in the podzol and grey-brown podzolic zones in the eastern provinces and in B.C. It is suggested that these variations should be designated as sub-zones rather than zones because several of the sub-zones may have characteristics in common with the soils of any one of the great soil groups. As many of the sub-zones are more or less transition zones from one major zone to another, it may perhaps be argued that the Dark brown soil zone should not be considered as a major zone, as it is a transition from the brown to the black. However, considering its importance and distribution, and the fact that it more or less corresponds to the chestnut great soils group, it is suggested that the dark brown zone should be continued to be recognized as one of the major soil zones.

Parent Material

As mentioned earlier, great variations in soils exist in nay one of the different zones or sub-zones. Some of the greatest of these variations are caused by differences in the parent materials of the soils. Numerous examples could be quoted of so-called “normal” soils of any one zone which greatly differ in morphological and chemical characteristics due to the effect of the parent material from which the soils have formed. In the case of the so-called “intrazonal” soils the effects of the parent materials on the characteristics of the individual soils are often even more pronounced than in the case of the “normal’ of “zonal” soils. The terms “normal” or “zonal” and “intrazonal” are too all embrasive to take care of these differences and it is suggested that the soils be grouped within a zone according to the nature of the parent material from which the soil has formed and which has given the soil some of the more important characteristics.

In describing the parent material two questions come foremost to our minds. First, How did it get there or what is its mode of deposition? Is the parent material residual material, glacial till, lacustrine or outwash deposits? Secondly, What is the nature of the parent material or, in other words, what is its composition, its ease of weathering and its consequent effect on the soil? It is difficult to determine the exact nature of the parent material, but where differences in soils can be attributed to differences in the nature of the parent material, these differences can be brought out by simple descriptive terms supplemented by such data as is available. The description of either the mode of deposition or the nature of the parent material alone is not sufficient to give an accurate picture.

Soils on similar parent material may vary according to local features of relief and soil climate, and according to other factors. These local soils usually vary from one parent material to another. Therefore, on any one parent material a number of soils are associated together forming a natural pattern which differs from a group of soils which are found associated on another parent material. It is suggested that this natural pattern of soils associated on one parent material be designated as a Soil Association. As an alternative the name “Soil Family” has been suggested by some but it should be pointed out that in this case the “Family” does not correspond to the “U.S. Soil Family” and its use would probably cause considerable confusion.