1. Introduction to Soils

2. Weathering
Formation of soil by processes such as weathering, organic matter accumulation ,and leaching (soil as a system)

3. Organic and Inorganic
Organic – dead plants and animals, waste products decompose (process of once-living material into dark-colored organic matter)
Inroganic – mechanical and chemical weathering of rocks (boulders, cobbles, gravel, sand, silt, or clay)

4. Soil Formation
Parent material (starting material of soil) – rock or sediment that weathers and forms soil
Climate – average weather of an area – precipitation, daily/average temps – affects weathering rates
Topography – shape and steepness of a landscape – water flow affects sedimentation
Biota – living things in a region – air and water pores formed by organisms speeds up weathering and decomposition or organic matter
Time – slow / constant process – thousands of years for a mature soil to form

5. Pores Pore spaces provide air and water for plants
Pores determine drainage and water storage
Sand > Silt > Clay
Which soil would swell the greatest amount after a rain – sand/silt size particles or silt/clay?

6. As soils age, they form distinct soil horizons and a soil profile
topsoil
subsoil
parent material

7. Soils are dynamic, they change over time
Parent
material
Young
soil
Mature
Old
Time

8. HORIZONS
A – contains most of the organic matter in the soil – excellent for plant growth
B – clay, other materials – water carries clay particles (small) and deposits below the upper layer
C – layered parent material – rocks or sediments

9. The Role of Climate
The balance between moisture and temperature is particularly important to the development of soils.
MOISTURE
how much
when
TEMPERATURE
season length
range of highs/lows

10. Houston, TX

11. High rainfall during warm temperatures
Water used by plants
Lots of plant growth
Darker topsoil
Houston soil

12. Gainsville, AL

13. High rainfall during cooler temperatures
Few plants to use water
Excess water leaches through the soil
Red/orange subsoil
Colors as a result of oxidation
Bama soil

14. Thin, light colored topsoil Little water reaches subsoil
Low rainfall
Little vegetation
Low plant growth
Thin, light colored topsoil
Little water reaches subsoil
Salts accumulate
White subsoil
(Orovada soil
from Nevada)
(Casa Grande soil
From Arizona)

15. The Role of Parent Material
Material from which soil forms:
bedrock
colluviam (sediments transported via gravity to the base of a slope)
alluvium (loose, eroded soil)
loess (windblown material)
Parent material influences mineral composition and particle size of soil.
(Arizona)

16. SOIL TEXTURE
The particles that make up soil are categorized into three groups by size – sand, silt, and clay.
Sand particles are the largest and clay particles the smallest.
Most soils are a combination of the three.
The relative percentages of sand, silt, and clay are what give soil its texture.

17. Particle size Smaller, finer particles (like clay)
hold water and nutrients,
including carbon
Coarser particles
don’t hold water or nutrients,
but they promote oxidation
(Arizona)

18. A clay loam texture soil, for example, has nearly equal parts of sand, slit, and clay.
Each texture corresponds to specific percentages of sand, silt, or clay. Knowing the texture helps us manage the soil.
There are 12 soil textural classes represented on the soil texture triangle. This triangle is used so that terms like “clay” or “loam” always have the same meaning.

19. Services by the Soil System
Food
Fiber
Filtration of gas & water
Water storage
Carbon Storage

20. Threats to Soils Include:
Erosion
Contamination
Sealing
Compaction
Loss of biodiversity
Salinization
Floods and Landslides
Sealing - destruction or covering of soils by buildings, constructions and layers of completely or partly impermeable artificial material

22. Soil Quotes
“How can I stand on the ground every day and not feel its power? How can I live my life stepping on this stuff and not wonder at it?” - William Bryant Logan from Dirt-The Ecstatic Skin of the Earth
“We abuse land because we regard it as a commodity belonging to us. When we see land as a community to which we belong, we may begin to use it with love and respect.” - Aldo Leopold, A Sand County almanac.
“We might say that the earth has the spirit of growth; that its flesh is the soil.” - Leonardo da Vinci