Physical weathering: Disintegration Chemical weathering: Decomposition Biological weathering: Disintegration & decomposition by biotic factors

2. Biotic factors in soil development

3. Introduction
Types of weathering
1. Physical weathering:
Disintegration
2. Chemical weathering:
Decomposition
3. Biological weathering:
Disintegration & decomposition
by biotic factors
Factors of soil development

4. Biotic factors
• 1. Roots of higher plants
• 2. Lichens
• 3. Mosses
• 4. Microbes - Bacteria, fungi, actinomycetes, etc
• 5. Insects
• 6. Earthworms
• 7. Animals
• 8. Man

5. Roots of higher plants

6. Lichens
• Lichen - Symbiotic association of
algae and fungi
• Both physical & chemical
weathering by rhizines
• Fungi producing acid helps to
break down rock mineral
• Minerals released from rock are
consumed by algae

7. Mosses
• Non flowering, non vascular
bryophytes
• Both physical & chemical
weathering by rhizoids
• Mosses absorbs CO2 from the
atmosphere and extract minerals
from the rock by secreting organic
acids

8. Bacteria, Fungi, Actinomycetes
• Decomposition of organic residues produces organic acids
• Respiration produces carbonic acids
• Some fungi produce siderophores, which can absorb various minerals and
nutrients from the soil

9. Insects
• Ants, termites, moles, etc - Physical weathering
• Create holes on the ground by excavation and movement
• More exposure of oxygen and water through these holes - enhances
weathering

10. Termites & ants
• Termites (Isoptera)
• Ant (Hymenoptera)
• Their pedological influence is largely
through the construction of nests,
galleries, soil sheetings and mounds
Awadzi, et al., 2004

11. Earthworms

12. Animals
• Burrowing mammels have an important role in the formation of soil
structure - Ecosystem engineers
• Improve soil structure by forming channels and pores
• Forms soil aggregates, fragmenting and mixing organic matter through out
the soil
Badgers (Meles meles) Beaver (Castor Canadensis)