1. Factors of Soil Development
Parent material
Climate
Topography
Organisms
Time

2. Parent Material The sediments or rock in which the soil develops
Influence
Soil texture
sandy sediments become sandy soils
Soil chemistry
mafic rocks become soils with higher levels of mineral nutrients

3. Climate The long-term conditions of temperature and precipitation
Influence
The degree of soil development
Warmer conditions enhance soil development
Wetter conditions enhance soil development
Chemical weathering and other chemical reactions
The vegetation that grows in the soil

4. Topography Slope steepness, slope orientation, and landscape position
Affects the separation of rainfall into infiltration and runoff
Steeper slopes have less infiltration and more runoff
Less infiltration means less soil development
More runoff means more surface erosion which slows down soil development

5. Topography Slope orientation Landscape position
Affects the amount of sunlight received
South-facing slopes are warmer which enhances soil development
Landscape position
Affects the internal drainage of the soil
Higher landscape positions have better drainage which enhances soil development

6. Organisms The plants and animals that live in the soil. Influence
Nutrient levels in the soil
Deciduous trees take up lots of nutrients which are then returned to the soil when leaves fall and decay
Coniferous trees do not take up many nutrients allowing those in the soil to be leached away
The structure (openness) of the soil
Allows better movement of air and water through the soil

7. Time
The length of time that soil-forming processes have been acting at a specific location
The longer the time, the greater the degree of soil development
Because soils develop from the surface downward
Erosion of surface horizons sets back the clock of soil development

8. How Do Soils Develop? From the ground surface downward…
Forming layers called soil horizons…
Through the
Addition
Transformation
Removal
of material to, within, or from a horizon.

9. The Soil Horizons O horizon A horizon E horizon B horizon C horizon
Dead and decaying organic matter
A horizon
Mix of organic and mineral matter – “topsoil”
Zone of removal
E horizon
Zone of extreme removal
B horizon
Clay-rich – “subsoil”
Zone of accumulation
C horizon
Weathered bedrock or minimally altered sediment
R horizon
Unweathered bedrock

10. Soil Profiles and Soil Series
The sequence of soil horizons present at a specific location
Defined by the type and thickness of horizons present
Soil Series
A named soil profile used for soil mapping
Soil Series are typically grouped together in Soil Associations