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What is Soil?
Soil
Soil Formation
• Multiple factors influence formation
• Loose top layer of our planet's crust that
supports plant growth
• A mixture of mineral and organic materials
plus air and water
Climate
• Temperature and Moisture
– Weathering processes
– Soil organisms
– Plant growth
– Decomposition rates
– Soil pH
– Chemical reactions in the soil
Living Organisms
• Intrinsically involved
– Add organic material
– Nutrient cycling – nitrogen cycle and role of
Rhizobium, actionmycetes, etc.
– Reduce size of litter
– Facilitate decomposition
– Aeration
Parent Material
• Refers to the rock and minerals from which
the soil derives.
• Effects the soil texture, chemistry and cycling
pathways.
• May be native or transported
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Topography
Time
• Physical characteristics of location
• After enough time, the soil may reach
maturity.
Soil Properties
•
•
•
•
•
•
Infiltration
Porosity & Permeability
Leaching
Structure
Texture
pH
Profile
Water
Water
High permeability
Low permeability
• Soil forming process operates from
top down
• Differences evolve at varying depths.
Soil Horizons
O – Organic material: leaf litter & humus
A – High biological activity, mineral
matter, humus present
E – Zone of leaching
B – Subsoil; zone of accumulation
Topsoil
C – Weathered parent material
R – bedrock
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Texture
Soil Quality
Texture
Nutrient
Capacity
Infiltration
Water-Holding
Capacity
Aeration
Tilth
Clay
Good
Poor
Good
Poor
Poor
Silt
Medium
Medium
Medium
Medium
Medium
Sand
Poor
Good
Poor
Good
Good
Loam
Medium
Medium
Medium
Medium
Medium
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