Soils are complex mixers forming the skin of the earth's surface. Soil is a dynamic layer in which many complex chemical, physical and biological activities are going on constantly. Soils become adjusted to conditions of climate, landform and vegetation, and will change internally when those controlling conditions change. Soils are products of weathering. Soils play a dominant role in earth's geomorphic processes in a cyclic manner. The characteristics of soils are very essential for several reasons. This module highlights these characteristics.

1. CHARACTERISTICS OF SOILS
By
Prof. A. Balasubramanian
Centre for Advanced Studies in Earth Science
University of Mysore, India

2. Soils are
• The products of weathering

3. Weathering
Breakdown of Rocks near the Surface
Chemical Alteration
• Solution & Leaching
• Biological Action
• Hydration
Mechanical
• Gravity
• Wedging: Frost, Plant Roots, Salt Crystal
Growth, Expansion of Hydrated Minerals

4. Differential
Weathering
and Erosion

7. Soil as a Dynamic Body
• Soil is a dynamic layer in which many complex
chemical, physical and biological activities are
going on constantly.
• Soils become adjusted to conditions of climate,
landform and vegetation, and will change
internally when those controlling conditions
change.

13. Soil Pedogenesis
• The kinds of soils that develop in a
particular area are largely
determined by five interrelated
factors: climate; living organisms;
parent material; topography; and
time .

17. Soil as a natural resource

18. • 1. Soils are complex mixtures of 5 major
components:
• minerals, water, air, organic matter, and
countless living organisms( microbial life).
• 2. Soils are the loose mineral or organic
materials 25% air, 25% water, 45% mineral
and 5% organic matter (humus, tiny living
organisms and sometimes plant residue).

19. • 3. Pedology: The study of soils, particularly their
formation, morphology, distribution and
classification is called as Pedology.
• 4. Pedogenesis: deals with the origin and
formation processes of soils and their
morphological characters.
• 5. The Skin of mother Earth: a product of
weathering from various parent rocks or as
transported materials from far off places by the
action of water, wind, glaciers and other agents.
Capable of supporting plant life and all life on
earth.

20. • 6. The soil is at the interface between various
spheres of the earth
• 7. Soil is always under the dynamic influence
of environmental factors
• 8. Importance (Functions) of soils: Soil
performs 7 major functions in almost many
ecosystems:
• 9. Soils and the earth's cyclic processes: Soils
play a dominant role in earth's geomorphic
processes in a cyclic manner.

21. • 10. Soils are characterised by many
properties:
• A) Physical Properties of soils:(1) Soil
separates and texture,
• (2) Structure of soil,
• (3) Weight and soil density,
• (4) Porosity of soil,(5) Permeability of soil,
• (6) Soil colour,(7) Temperature of soil, and
• (8) Engineering properties like Soil Plasticity,
Compressibility and Erodibility.

22. • (B) Chemical Properties of Soils, including:
• (1) Inorganic matters of soil,
• (2) Organic matters in soil,
• (3) Colloidal properties of soil particles,
• (4) Soil reactions and Buffering action, and
• (5) Acidity/ Alkalinity/ salinity/ sodicity
• C) Soil moisture
• D) Soil Profile( vertical distribution of soil
horizons),
• E) Soil Air,
• F) Soil Morphology.

24. Importance of Soils:
• 11. Soil is an engineering material for construction
• 12. Soils are ecosystems: Soils are a host of small, medium, and
large organisms. Many mammals, birds, insects, and protozoa live in
it.
• 13. Soils are Need for plant growth:Soils are the primary provider
of nutrients and water for much of the plant life on earth.
• 14. Soils are Clay Factories: Clays are are often active, and
chemically reactive with ions, water, and other particles.
• 15. Soils are Service Providers:They filter and remediate pollutants.
They cycle and recycle nutrients and wastes.
• 16. Medium for plant growth:
• 17. Habitat for many insects and other organisms:
• 18. Filtration system for surface water:
• 19. Carbon store and maintenance of atmospheric gases:

25. Soils may be spoiled on earth
• 20. Soils may get degraded and Polluted:
• 21. Many human activities degrade and
pollute soils.
• Human Pressure on Soils: The increasing
human population is placing greater pressure
on soil and water resources and threatening
our ability to produce sufficient food, feed,
and fiber

26. • 22. Erosion is among the great causes of soil
degradation.
• 23. Soil degradation: Salinization and
desertification are major causes of soil
degradation in arid areas.
• 24. Salinization is the builtup of salts in soils
to a point that they destroy the physical and
chemical properties of soil and make it
impossible for plants to take up water from
the soil. Salinization is often associated with
improper irrigation.

27. • 25. Desertification is caused by a combination
of climate changes and human-induced soil
degradation(such as through overgrazing).
• Soils have a great capacity to filter
and remediate pollutants, but applications of
pollutants to soils often exceed this capacity.

29. Characteristics of soils vary very widely
• 26. Soil Taxonomy: system of classification
• TYPES: There are many types of soils, usually
placed in classes (types) based on their color,
profile, texture, composition or structure.
Each soil type is formed differently, and can be
found in specific places on the earth’s
immediate surface, mid and deep under the
surface.

30. • 27. Sand, silt, and clay are the basic particles
in a soil. Most soils are made up of a
combination of the three.
• The texture of the soil, how it looks and feels,
depends upon the amount of each particle in
that particular soil.
• 28. The type of soil varies from place to place
on our planet and can even vary from one
place to another in your own backyard.

31. • 29. Soil erosion, caused by wind and rain, can
change land by wearing down mountains,
creating valleys, making rivers appear and
disappear. It is a slow and gradual process that
takes thousands, even millions of years.
• 30. Importance of Soil Conservation