soil formation, profile and characters are discussed

1. By,
BHANUPRIYA R
CLASS NO.212

2. • GK ‘ edaphos ’ = ground , soil
• Soil-latin word –solum meaning earthy material.
• Study of soil is known as Pedology or Edaphology
• The factors which relate to structure and composition of soil are called edaphic
factors.
• Soil is a very complex medium.
• A good fertile soil contains,
-mineral particles
-organic matter
-water
-air

3. The process of soil formation from the rocks can be represented as
follows:
Consolidated parent rocks (weathering) small particles of
parental material
mature soil with (pedogenesis) or
profile differentiation regolith
 Soil are derived from parent rocks by the process called weathering.
 The products of weathering are called regoliths.
 These particles under pedogenic influence develop into mature soil

4.  The vertical layered structure of soil is called soil profile.
 Layers of soil is horizon – 6 horizons
1.O horizon (organic horizon or litter zone)
2.A horizon (Top soil)
3.B horizon (Sub soil)
4.C horizon (Weathering rock)
5.D horizon (Weathering rock)
6.R horizon (Bed rock)

5. O horizon
• Uppermostorganic matter
• Dark crumbly material that result from decomposition of
organic matter.
A horizon
• It is a top soil-zone of eluviation(leaching)
 A1-horizon
• Rich in humus, dark coloured
• Rich in organic material,bactera and fungi
 A2-horizon
• Zone of maximum leaching
• Light coloured and contains coarse sand

6. Continued……
A3-horizon
•Transitional region from A zone to B-zone
B-horizon
•Zone composed of minerals and humus
•Zone of illuviation
•Consist of B1,B2,B3-precipitation of
transported materials
•Rich in clay, roots of shrubs and trees
reach up to this horizon
C – horizon
•A thick layer
•Also called regolith or parent rock
•Contains large mass of weathered mineral
material
 D-horizon
•Rocks in active weathering state
R-horizon
•Lowermost layer(bed rock)
•Composed of unmodified parent material.

7. SOIL TEXTURE
• Soil texture refers to the proportion of
mineral particles of various size.
• THREE TYPES OF SOIL:
 Sandy soil contains large particles.(psammophytes)
Loamy soil is a mixture of sand and clay.
Clay soil are made of very small particles.

8.  DENSITY :depends on extent of weathering and particle arrangement.
 POROSITY : is the space between soil particle in a given volume.
-pore spaces are necessary for holding water and for the gaseous exchange.
 PERMEABILITY: determines the movement of water through pore spaces.
-it is higher in loose soil and lower in compact soil.
 SOILATMOSPHERE: is the air that fills the pore spaces in the soil.
-soil air has higher CO2 content and lower O2 content .
 SOIL TEMPERATURE: affects physico-chemical and biological processes of soil.
- influenced by soil colour ,texture and water.
 SOIL COLOUR : soil colour may be inherited from the parental material.

9. • All the water available in soil is called soil water.
• It maintains the texture of soil.
• Supports soil organisms
TYPES OF SOIL WATER
-Gravitational water : free water moving down due to gravity
-Hygroscopic water : water held tightly by soil particles
-Capillary water : water held by capillary forces
-Combined water : water chemically bond to soil surface
• The total amount of water present in the soil is called holard
• The amount of water that plants can absorb is called chresard
• The amount of water which cannot be absorbed by plants is called echard

10.  CHEMICAL COMPOSITION : consist both organic and inorganic components.
• Inorganic: mainly Ca,Mg,Fe,Al,Si,Na and traces Mn , Zn ,Co , Cu. It
influences the pH of soil.
• Organic :organic matter and humus forms the organic components.
SOIL PH : soil pH ranges from 2.2-9.6
-warm and dry soil-basic soil
-acidic soil occur in high rainfall regions

11. Soil organisms
• Organisms present in the soil is called soil organisms.
• Important groups of soil organisms,
SOIL FLORA SOIL FAUNA
Bacteria Protozoans
Soil fungi Nematodes
Algae Rodents&earthworms
Root , rhizoid and
Rhizome bearing – Burrowing vertebrates
Higher plants

12. Based on size, soil organisms are grouped under three categories:
a) Microbiota :include algae, bacteria, fungi and protozoa
b) Mesobiota : include nematodes, insect larvae ,soil mites e.tc.
c) Macrobiota : include roots of plants,larger insects & earthworm .
EFFECTS OF SOIL ORGANISMS ON SOIL
 Nitrogen fixation
 Decomposition
 Antibiosis
 Soil mixing
 Soil born diseases

13. • Punnen kurian venkadathu ,2000, ENVIRONMENTAL BIOLOGY
AND ETHOLOGY , Zoological society of kerala,Udaya offset press.
• G S Dhaliwal , G S Sangha ,1996, FUNDAMENTALS OF
ENVIRONMENTAL SCIENCE , Kalyani publishers, New Delhi
• K K Bhaskaran , A R Ajith kumar Ramesh, 2014, ENVIRONMENTAL
SCIENCE AND ECOTOUISM , Manjusha publications , calicut.
• .