1. SOIL
Man, despite his artistic pretensions, his sophistication, and his many accomplishments— owes his existence to a six-inch layer of topsoil and the fact that it rains.

2. Dirt: A Natural Resource
We know more about the movement of celestial bodies than about the soil underfoot.
-Leonardo da Vinci

3. Definition
Solid earth material that has been altered by physical, chemical and organic processes so that it can support rooted plant life.
Engineering definition: Anything that can be removed without blasting

4. Soil Texture There are three noticeable parts Sand (.05 – 2 mm)
Silt ( mm)
Clay (.002 mm)

5. Dirt: A Natural Resource

6. Physical weathering breaks rocks into small mineral particles

7. Chemical weathering dissolves and changes minerals at the Earth’s surface.

8. Decomposing organic material from plants and animals mixes with accumulated soil minerals.

9. Soil Composition
Soil, on the average, consists of 50% mineral and 5% organic matter.
The remainder is pore space taken up by air or water.
This is just an average!

10. Soil Composition
During a precipitation event or snowmelt, water infiltrates into soil through the pores space and pores become filled. As the soil begins to drain or dry, air replaces water in the pores. On average, soil contains 50% pore space which can be evenly divided between air and water.

11. Soil Composition
Particle size determines the amount of air & water contained in soil

12. Soil Composition
Pores between the solid materials hold liquids and gases that are essential for plant and microorganism growth, and solid materials hold or provide nutrients that can become accessible for organism growth.

14. Five Factors that Influence Soil Formation
Climate
Organisms
Parent Material
Topography
Time

15. Parent Material The earthen materials that make up the soil. rocks
volcanic deposits
sediments
minerals
sandstone will form coarse sandy soil.
soft shale will turn into heavy clay soils
granite bedrock produces a sandy loam.

16. Climate More moisture from rain will speed up soil development
Too much can wash away nutrients.
Dry climate soils become very fertile the first time they are irrigated, but if the evaporation rate is high, salts will rise to the surface and reach a toxic level to plant life.
A freezing and thawing cycle will speed up the crumbling of rocks.
Warmth increases organism activity and chemical processes will speed up.

17. Living Organisms
Animals and plants are the source of organic matter and the nutrients.
These are released into the soil either by physical decay after death or from animal wastes like manure. 
The organic remains from the surface are worked by microorganisms into material that is incorporated into the soil.
There is also the direct altering by sub-soil animals like moles and earthworms.

18. Topography
Soils on the side of hills tend to be shallow, due to erosional losses.
Soils on the tops of hills and in valleys tend to be deep
There is material accumulation from downward leaching from the tops of hills, and the collection of greater quantities of water in the low lying areas.
Soils that get more sun exposure will be drier.
The natural vegetation and growth will also affect composition.

19. Time
Time is the encompassing factor that binds all of these materials and interactions together. Soils can go through many changes over the course of years.
It takes hundreds of years to form one inch of soil from parent material.

20. Time This is why soil conservation is so important
U.S. Department of Agriculture estimates that it takes 500 years to form an inch of topsoil.
That’s less than 0.01 mm yr-1

21. Soil Profile A cross-section of soil is called a soil profile
The distinct layers of soil are called soil horizons

22. Soil Horizons O Horizon A Horizon E Horizon Organic
consists of leaf litter and other organic material lying on the surface of the soil
A Horizon
Top Soil
the most productive layer of the soil.
Conservation efforts are focused here!
E Horizon
Eluviated (leaching layer)
Where minerals and organic matter leave this layer and move into the next lower layer

23. Soil Horizons B Horizon C Horizon R Horizon Subsoil
Usually lighter in color, dense and low in organic matter.
More minerals
C Horizon
Consists largely of weathered parent material.
R Horizon
Rock (Bedrock)
Un-weathered sediment of pure parent material.

24. Soil Development

25. Soil Development ADDITIONS Inputs from outside ecosystem
Atmospheric inputs
Precipitation, dust, deposition
Horizontal inputs
Floods, tidal exchange, erosion, land-water movement
Inputs from within ecosystem
Litterfall and root turnover

26. Soil Development TRANSFORMATIONS Decomposition of organic matter
Humification to form complex organic matter
Weathering of rocks
Physical weathering
Fragmentation of rock
Freeze-thaw; drying-wetting; fire
Physical abrasion
Abrasion by glaciers
Chemical weathering
Dissolves primary minerals
Forms secondary minerals

27. Soil Development TRANSFERS
Translocation of materials within the soil profile is primarily due to gradients in water potential and chemical concentrations within the soil pores.
Soluble minerals, colloidal material, organic compounds, and iron may move up or down the profile, between horizons, with water movement.
Biological activity may cause gradient in the chemical composition of the water and air- filled pores of the soil.

28. Soil Development LOSSES
Modern rates of soil loss are 100 to times rates of soil formation (typically mm yr-1 to cm yr -1 in agricultural settings).
Most losses occur by leaching (fertilizers.) Water moving through the soil (rainfall or irrigation) dissolves certain minerals and transports them into deeper layers.
Carbon dioxide is consumed by growing plants, but lost to the soil as fresh organic matter decays.
When soil is wet, nitrogen can be changed to a gas and lost to the atmosphere. 
Solid mineral and organic particles are lost by erosion

29. A nation that destroys its soils, destroys itself.
– President Franklin D. Roosevelt, Feb. 26, 1937.