The document outlines the classification and taxonomy of soil, emphasizing the importance of accurate soil identification for effective conservation and sustainable use. It discusses various historical classification systems, modern approaches based on soil properties, and the establishment of a comprehensive soil taxonomy consisting of orders, great groups, sub-groups, families, and series, which all reflect specific soil characteristics. Additionally, it highlights the role of diagnostic horizons in soil classification and the practical implications of understanding soil associations and catenas in agriculture.

1. PRESENTED BY
CHITRA DEVI A
2022520006

2. Pedon and polypedon
• Basic unit of soil classification
• Smallest sampling unit that displays the full range of properties characteristic of
a particular soil
• Pedons occupy from about 1 to 10 m2 of land area

3. Why need soil classification and taxonomy?
• Classification allows scientist to accurately identify individual soil wherever they
are.
• Taxonomy provides basic understanding about the components of different soils
which is necessary for effective decision-making about conservation and
sustainable use

4. Early system of soil
classification

5. Historical Developments In Soil Classification
1. Economic classification
2. Physical classification
3. Chemical classification
4. Geological classification
5. Physiographic classification

6. 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 colour and texture of the soil combined with
irrigation potentialities.
• Such a system was of little importance and became obsolete when the land use
changed.

7. 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 zonal soil category.

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

9. Geological Classification:
• This system of soil classification was based on the presumed underlying parent
material.
• According to this system, two broad groups of soils were recognised:
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 applicable to processes of soil
formation controlled by active factors of soils formation (climate and vegetation) which
dominate over the influence of parent material

10. 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.

11. Modern System Of Soil
Classification

12. MODERN SYSTEM OF SOIL CLASSIFICATION
• The first classification was proposed by dokuchaev (1870): soil is a natural body divided the soil
into three categories
1. Normal (zonal): formation influenced by climate and vegetation
2. Transitional (intrazonal): more developed than azonal. Formation controlled by local factors like
parent material and topography
3. Abnormal (azonal) : poorly developed this approach was based on the principle of soil genesis,
role of vegetation and climate

13. Marbut’s Morphogenetic System:
• Both soil morphology and soil genesis
• Introduced the concept of “great soil group”.
• Classification based on their own intrinsic properties.
• The highest category was divided into two classes
1. Pedalfers- Aluminium and iron accumulation (highly leached soil)
2. Pedocals- calcium carbonate accumulation (soils of arid and semiarid)
• But this system was based on assumed soil genesis which could not find places for most of the
soil.

14. Baldwin And Associated Genetic System:
• They emphasized the marbut’s system and returned to the zonality concept.
• They gave emphasis on soil as a three dimensional body.
• They introduced the concept of “soil family” between the great soil group and
soil series.
• The concept of “great soil group” was revised.
• But still this system was also not completely based on soil measurable
properties.

15. Three ORDERS In This System:
1. Zonal or “normal” soils -climate inputs dominate a soil’s genesis -soil is in equilibrium with the
climate/vegetation.
Eg.:
• Podzols – cool climates, coniferous forest
• Desert soils
• Laterite soils – red tropical soils

16. 2. Intrazonal soils (local conditions: topography and/or parent material) - salts,
wetness or limestone bedrock overwhelm the soil’s genesis.
Eg.:
• Gley soils – wet soils
• Peat soils
3. Azonal soils - too young, dry or sandy to have developed into zonal soils.
Eg.:
• Dry, sandy soils
• Shallow-to-bedrock soils
• Alluvial soils (young parent materials)

17. • 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.

19. Major Limitations Of The Genetic Systems
The two highest categories were defined in genetic terms not on soil properties.
The great soil group concept were qualitative.
In definitions, more emphasis was given on properties of virgin soils which got
modified by use.
The nomenclature was evolved from many languages and it was difficult to
name the intergrades.

20. Soil Taxonomy (Comprehensive System Of Soil
Classification)
• System based on the measured or observed soil properties.
• Surface and subsurface diagnostic horizons.
• Moisture and temperature regime.
• Color, texture, structure.
• Organic matter, clay, iron, aluminium oxides, silicate clays, salts, ph, base saturation.
• Soil depth.

22. Advantages Of New Comprehensive System Of Soil
Classification Over The Earlier System:
Unlike the genetic systems, the new comprehensive system is based on soil properties. An
attempt has also been made to define all classes in terms of soils properties.
The new comprehensive system considers properties affecting soil genesis which is the
backbone of this system.
Most of the words used for nomenclature are derived from greek and latin which are most
logical and it helps in relating the place of taxon in this system and in making its interpretations.
In this new comprehensive system, the sub-group (new category) has been introduced for the
expressions and recognition of soils that are a continuum with gradual change in many
properties.
Unlike the genetic system, it is an orderly scheme without prejudices and facilities easy
memorizing the objects.

23. Orders Of Soil Taxonomy
• These twelve orders are
differentiated by the presence or
absence of diagnostic horizons.
• All orders end in sol

24. Sub-orders
• All twelve orders have been classified into different sub-orders primarily on the basis of
morphological, chemical and physical properties the reflect either the presence or absence of
waterlogging or genetic differences due to climate and its partially associated variable,
vegetation.
• The names of sub-orders are formed by combining two syllables, the first syllable signifying the
formative elements of the sub-order and the second syllable that of the formative elements of
the order.
e.g. The sub-order argids consists of two syllables, arg for argilla and id for aridisol.

25. Great Groups
• In the great-group, the basis of subdivisions is the consideration of the whole
soil, the assemblage of horizons, and the most significant properties of the
whole soil, selected on the basis of the number and importance of accessory
properties.
(i) Close similarities in kind, arrangement and degree of expression of horizons.
(ii) Close similarities in soil temperature and moisture regimes.
(iii) Close similarities in base status.

26. Sub-groups
• These are sub-divisions of great groups.
• Three kinds of sub-groups have been recognized viz.
• (I) typic group;
• (Ii) integrades and
• (Iii) extra-grades.
• The typic sub-group is thought to typify the great group and does not show any transition to
another sub-group. e.g. Typicnatrargids.
• Intergrade-sub groups are those that belong to one great group, but have some properties of
another order, sub-order, or great group. e.g. Ustochrepts.
• Extragrade subgroups have important properties that are not representative of the great group,
but that do not indicate transitions to any other known kind of soil. e.g. Pergelliccryorhent (a
permanently frozen layer).

27. Families
• The family category of soil classification is the least well-defined.
• However, properties important to the growth of plants are used to differentiate families.
• This category permits the grouping of members of sub-groups having common similar properties
such as particle size distribution, mineralogy, temperature regime, ph and thickness of the soil
permeable by roots.

28. Series
• Soil series represents the properties of a contiguous pedon (smallest volume of soil material) in
the recognised polypedon (many pedons).
• It is the most specific category.
• The soils of any one series have similar profile characteristics.
• A series is a group of soils developed from the same kind of parent material by the same genetic
combination of processes and whose horizons are quite similar in their arrangement and general
characteristics.
• The series are named after the geographic name of the place where it was first recognised or
where they have wide extent of distribution, e.g. Jodhan loam.

29. Soil Phase
• A phase is a sub-division on the basis of some important deviation
such as surface texture, erosion, slope, stoniness, or soluble salt
content.

30. Soil Associations And Catenas
• In the field, soils or different kinds are commonly found together.
• Such an association of soils may consist of a combination from different soil orders.
• Soil associations are important in a practical way since they help to determine combinations of
land-use patterns which must be utilized to support a profitable agriculture.
• Well-drained, imperfectly drained, and poorly drained soils, all of which have developed from
the same parent materials under the same climatic conditions, are often found closely
associated under field conditions.
• This association on the basis of drainage or of differences in relief is known as a catena and is
very helpful in practical classification of soils in a given region.

31. Epipedons or diagnostic surface horizons
• Among the most significant of soil properties used as a basis for classification is
the presence or absence of certain diagnostic soil horizons.
• Six epipedons are recognised i.E. Mollicepipedon, umbricepipedon, anthropic
epipedon, histicepipedon, plaggenepipedon and ochric-epipedon.

33. THANK YOU