Soil Classification –

 Urvara v  Users 

•In India, the soil had been classified from the ancient period itself even though it was not as detail as the modern classifications.

•In the ancient period, the classification was based on only two things; whether the soil is fertile or sterile. Thus the classification was:

1.Urvara [fertile]

2.Usara [sterile]

Soil Classification – Agencies involved

•In the modern period, when men started to know about the various characteristics of soil they began to classify soil on the basis of texture, color, moisture, etc.

•When the Soil Survey of India was established in 1956, they studied the soils of India and their characteristics.

•The National Bureau of Soil Survey and the Land Use Planning, NAGPUR an institute under the control of the Indian Council of Agriculture Research did a lot of studies on Indian soil.

Category 1:

Early Systems of Soil Classification:

Early systems of soil classification were very simple and practical.

1. Economic Classification: One of the earliest systems of soil classification, adopted by the Revenue Department, for grouping soils according to their productivity was for purpose of taxation. The criteria used were soil color and texture of the soil combined with irrigation potentialities. Such a system was of little importance and became obsolete when the land use changed.

2. Physical Classification: It is one of the earliest systems and was based on soil texture, a property associated with soil productivity. This system of soil classification was applicable to the zonal soil category.

3. Chemical Classification: The grouping of soils based on chemical composition has not been used to a great extent for practical purposes. Still, soils were grouped as calcareous soils, acid soils, and sodic soils, etc. But these characteristics do not permit to the classification of all kinds of soils occurring in nature.

4. Geological Classification: This system of soil classification was based on the presumed underlying parent material. According to the Geological Classification system, two broad groups of soils were recognized:

(i) Residual or sedentary soils-developed in situ from the underlying rocks.

(ii) Transported soils-developed on unconsolidated sediments, like alluvium, colluvium, or Aeolian materials. The system of soil classification, however, does not apply to processes of soil formation controlled by active factors of soil formation (climate and vegetation) which dominate over the influence of parent material and thereby upset the geological soil classification.

5. Physiographic Classification: According to this system, the characteristics of the landscape were considered and so various geomorphic terms such as levee soils, basin soils, terrace soils, mountain soils, hilly soils, upland soils, and lowland soils were introduced to classify soils. A classification based only on physiography may have limited value as two or more soil groups with different properties may be classified in one group.

6. Other Systems: Several other systems of soil classification based on varying criteria were applied from time-to-time. For example,

Based on Organic Matter as Inorganic or mineral soils, and Organic soils

Based on Soil structure as:

Single-grained soils, and Aggregated soils.

Besides this, soil classification based on other parameters like, humidity,

vegetation and temperature have also been made.

Category # 2.

Recent Systems of Soil Classification:

In the later part of the 19th century and early part of the 20th-century Dokuchaiev (1900), Joffey (1912), Marbut (1935) classified soil on the basis of zonality, their own properties, and morphology emphasizing the need for examination of actual soils for their characteristics like soil color, texture, structure, consistency, drainage conditions, etc. respectively. Marbut also emphasized the concept of pedalfers and pedals.

Pedalfer: Soil that is characterized by an abundance of aluminum and iron oxides. Pedalfers are common in humid regions and are deposited in the B horizon of ABC soils, through leaching.

Pedocal is a subdivision of the zonal soil order. It is a class of soil that forms in semiarid and arid regions. It is rich in calcium carbonate and has low soil organic matter.

The major defect of Marbut Morphogenetic soil classification was that the system was based, in part, on assumptions concerning soil genesis. Many of the soil series recognized in the United States (U.S.) could not find a place in Marbut systems of classification of soil.

Category # 3.

Baldwin and Associate’s Genetic Approach:

Marbut’s morphogenetic soil classification system was revised and elaborated by Baldwin, Kellogg,
and Thorp (1938).

Orders of Genetic Approach:

After modification, the soils can be grouped into three orders namely, zonal, intra-zonal and azonal based on the zonality concept developed by Russian soil scientist Dokuchaiev.

Zonal Soils: Zonal soils were groups of soils developed under similar climate conditions and distributed in a climatic belt. Soils in this group possess well-developed profiles reflecting the influence of climate and vegetation. The only differences due to the parent material are rendered subordinate by dominating climate influences. For example, laterite soil, podzol soil, chernozem soil, etc.

Intra-Zonal Soils: The soils occur within a zone, but reflect the influence of some local conditions, such as topography and/or the parent material. Under these conditions, the characteristics of soils impacted by the local conditions and dominant viz. excess of water, salt, calcium carbonate, etc. For example, saline-sodic and saline-sodic soil, etc.

Azonal Soils: The soils have poorly developed profiles because of time as a limiting factor. The group includes young soils without horizon differentiation so the soils could not be grouped in any one of these two orders (zonal and intrazonal) and were placed in a separate order known as azonal soils. Example alluvial soils.

These three orders were further divided into nine (9) suborders on the basis of specific climatic and vegetative regions. Each of the sub-order, in turn, was divided into great soil groups having expressions of more specific conditions. The great soil groups were further sub-divided into numerous soil series and soil types.

The new comprehensive system of soil classification according to the 7th approximation

In order to overcome different anomalies in the earlier systems of soil classification, a new comprehensive system has been developed. Initially started in 1951, several approximations were made after taking critical suggestions from pedologists of different countries. The 7th Approximation was published in 1960 with supplements in 1964 and 1967.

Soil Taxonomy: A Basic System of Soil Classification for Making and Interpreting Soil Surveys was published in 1975. The 7th Approximation lays more stress on the morphology of soils themselves rather than on the environmental factors.