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1. Two Approaches in the Study of
Soils
• Edaphological approach – Greek :
edaphos (ground, soil) Study of soil with
emphasis on their practical use, especially
in relation to plant growth and
development. Incudes Soil Fertility (as well
as chemical and physical properties
related to fertility)

2. Two Approaches in the Study of
Soils
• Pedological approach – Greek : pedos
(earth, soil) Study of soil as a natural body,
with principal interest on characteristics
and differentiation of properties. Includes:
Soil Survey, Classification, Morphology,
Formation and Development

3. In this lecture
• Soil Genesis, Composition and
Development
• Soil Morphology and Classification
• Soil Physics
• Soil Chemistry and Mineralogy
• Soil Organic Matter and Microbiology
• Soil Fertility Management and
Conservation

5. Three Phases of Soil
• Solid Phase
– Soil solid particles
– Mineral and Organic Matter
– Different shapes, size and arrangement
– Particulate and aggregate
– Mineral particles/fragments/separates: SAND,
SILT, CLAY
– Organic Matter (OM): humic and non-humic
substances

7. Three Phases of Soil
• Solid Phase
– Aggregation/Flocculation: binding of particles
together, forming peds. OM serves as glue,
favored by Ca, destroyed by Na, a dispersing
agent
– Pores: interconnected space in between solids
– Micropores: small pores within a ped, occupied
by water
– Macropores: large pores in between peds,
occupied by air when moisture is at FC

8. Three Phases of Soil
• Liquid Phase
– Soil water/moisture/liquid
– Catalyst of weathering
– Contains dissolved ions and gasses
– Occupy all pores during saturation
• Gaseous Phase
– Soil air composed of 78% N2, 20% O2, 0.5%
CO2
– Atmospheric air: 78% N2, 20% O2, 0.02% CO2

9. Three Phases of Soil
• Soil Solids (50%)
– Mineral (45%) from weathering of rocks,
source of plant nutrients, except N, C and O
– OM (5%) from decayed plants, animals,
detritus, major source of N (98%)
• Soil Air (20-30%) for root respiration
• Soil Water (20-30%) solvent of nutrients