The document discusses the history and purpose of soil taxonomy and early soil classification systems. It explains that soil taxonomy is the basic system for interpreting soil surveys, developed by the US Soil Survey Staff led by Guy D. Smith. Early systems included economic, geological, physical, chemical, and physiographic classifications. However, these systems were limited and did not consider all factors influencing soil formation. Soil taxonomy was established in 1975 to provide a comprehensive system that defines classes based on observable soil properties and considers all genetic factors.

1. SOIL TAXONOMY, PURPOSE AND
EARLY SOIL CLASSIFICATION
SYSTEM

2. SOIL TAXONOMY
 It is the basic system of soil classification for interpreting soil
survey.
 The U.S. Soil Survey Staff under the leadership of Guy D. Smith has
developed a Comprehensive System of Soil Classification.
 Initially started in 1951, several approximations were made and a
comprehensive system of soil classification, popularly called the 7th
approximation was published in 1960 with supplements in 1964 and
1967.
 In 1975, the system was brought out as soil taxonomy (Soil Survey
Staff, 1975) and the 2nd edition was published during 1994 and the
same is being followed till today.

3. SOIL TAXONOMY PURPOSE
 Efforts have been made to define all classes in terms of soil properties that exist
today.
 It considers all such properties which affect soil genesis or are the outcome of soil
genesis. Soil genesis forms the backbone of the comprehensive system. But it does
not appear in the definition of the taxa.
 The nomenclature used in coining words is derived from Greek and Latin
 A new category i.e., sub group has been introduced to define the central concepts
of great groups and their intergrades
 Unlike the Genetic System, it is an orderly scheme without prejudices and and
facilitates easy remembering of the objects.

4. SOIL CLASSIFICATION
 The earliest known soil classification system in the world can be
find in an ancient Chinese book Yugong (2,500 y.b.p.), where soils
of China were classified into three categories and nine classes based
on soil color, texture and hydrologic features; the classification was
used for land evaluation
 Soil classification is grouping of object orderly and logical manner
into classes based on properties of soil for the purpose of studying
them.

5. 01 02
03 04
ECONOMIC
CLASSIFICATION
GEOLOGICAL
CLASSIFICATION
PHYSICAL
CLASSIFICATION
EARLY SYSTEM OF SOIL CLASSIFICATIONS
05 06
CHEMICAL
CLASSIFICATION OTHER SYSTEMS
PHYSIOGRAPHIC
CLASSIFICATION

6. ECONOMIC CLASSIFICATION
 It is the grouping of soils based on their productivity for the purpose of
taxation, adopted by the Revenue Department.
 The criteria used were soil colour and texture in combination with the
potentialities for irrigation.
 Eg.. Soils suited for rice, groundnut etc.,
 The system was of little importance and turned obsolete when the land
use changed.

7. PHYSICAL CLASSIFICATION
 It is grouping of soils based on their texture a property closely associated
with soil productivity and management. Eg.Loamy soil, sandy soil and clayey soil.
CHEMICAL CLASSIFICATION
 The grouping of soils by their chemical composition has not been used to great
extent as the data on soil analysis cannot be classified according to any definite
pattern.
 Still soils were grouped as calcareous soils, gypsiferous soils, acid soils, alkaline
soils etc.
 These characteristics do not permit to classify all kinds of soils occurring in nature.

8. GEOLOGICAL CLASSIFICATION
In the 18th and 19th centuries, geologists and geographers recognized close relationship
between soil and its parent rock and proposed classification system based on the presumed
underlying parent material. According to this system, two broad groups of soils are
recognized.
 RESIDUAL OR SEDENTARY SOILS : The soils developed in-situ from the
underlying rock, such as granite soils, soils from sandstone, limestone, basalt etc.,
 TRANSPORTED SOILS : The soils developed on unconsolidated sediments such As
alluvium colluvium or Aeolian.
 The system failed to recognize the influence of active soil forming factors like climate
and vegetation on the parent materials. Eg. Granite rocks in the temperate region results
in podzols whereas in tropical areas results in laterite soils.

9. PHYSIOGRAPHIC CLASSIFICATION
It is grouping of soils based on the characteristics of landscape as terrace,
mountains, valley, upland and lowland etc., the limitations of this systems is
that two or more soils may develop in same landform
OTHER SYSTEMS
 Based on organic matter content as :
Inorganic or mineral soils and Organic soils
 Based on soil structure:
 Single –grained structure
 Aggregated soils
Based on moisture or humidity, vegetation and temperature –
Arid soils, humid soils, sub humid soils, grassland soils, forest soils etc.,

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