1. Soil Profile & Horizons
Environmental science

2. Soil Profile and Soil Horizons
Soil Profile – I a series of horizontal layers in the soil that differ in chemical composition, physical properties, particle size and amount of organic matter (Text, p 392).
There are 11 orders with distinct soil profiles
These 11 orders cumulatively are known as soil taxonomy

3. Soil Profile and Soil Horizons
Each recognizable layer is known as a horizon
There are 3 primary horizons categorized by capital letters A,B,C.
Not every profile has an E horizon which is normally found between A and B. Horizon O can also be found above horizon A. While R is the bottom of the soil profile

4. Horizon A Topsoil A Horizon
AKA Topsoil (Mineral particles & organic matter)
This is the best environment for plants
Can have an additional layer known as an O horizon (Organic matter that has not been decomposed)
A Horizon can vary in depth depending on topography, vegetation, climate
Water moves through the A layer carrying organic matter and minerals to lower layers. This is called leaching
Soils and Our Environment p

5. E Horizon – Eluvial Horizon
The E horizon occurs as a result of leaching of clays and organic substances.
Lacks minerals and nutrients found in A and B
Lighter in color
Common in high rain fall areas
Soils and Our Environment p

6. B Horizon Subsoil AKA Subsoil Fewer organisms and organic material
Accumulates much of the nutrients leached from A and E.
In many occasions there are higher amounts of clay than Horizon A ALWAYS higher amounts of clay than B
Good source of nutrients for root systems that can reach this horizon
Soils and Our Environment p

7. Horizon C – Parent Material Substratum
Weathered parent material not affected by soil-forming processes
The breakdown of parent material can happen from
Mechanical/physical Weathering
Chemical Weathering (Text, p. 292)
No organic material
Chemical composition of parent material effects pH of soil
Limestone – neutralize acids
Granite – unable to neutralize acids
Soils and Our Environment p

8. R Horizon Bedrock Bed rock such as: Igneous – Cooled molten rock
Some rich in magnesium and Iron.
Chemical weather by oxidation
Sedimentary – usually much softer and porous
Chemical weathering by hydrolysis (dissolving minerals)
Metamorphic – Formed under intense heat and pressure
Slate, marble, quartzite
The harder the rock the slower it is to weather
Soils and Our Environment p , (Cornell University)

11. Each Order has a different Soil Profile
Horizon Differences caused by:
Accumulation of Humus (Organic material)
Leaching
Production/accumulation of more clay
Accumulation of other minerals
Soils in Our Environment p. 34 & 46

12. Fun Fact
Only 5 % of soils remain in their original location (residual location)
NRCS Soil Formation

13. Soil Degradation and Erosion
Erosion of exposed soil by wind, water or ice Text, p. 292
Most likely to occur in areas of vegetation loss
Desertification – farming, mining, overgrazing
Prevention – No till farming, strip farming , Polyface Farms (Joel Salatin), using livestock to stop desertification (Allan Savory )
Deforestation – logging and farming
water run off
Wind blown soils
Chemical Application – oils, gasolines herbicides
Reduce plant growth ultimately reducing organic materials
On the bright side NRCS has documented a decrease in erosion rates in farm production regions.
Text, p. 299

14. Picture from FOA