1. Soil
A recipe for soil

2. What is soil? Soil is a MIXTURE of:
Weathered rock and mineral fragments
Organic material such as leaves, twigs, dead worms, bacteria, fungi, insects
Air
Water

3. Organisms don’t just live in the weathered rock but they help it become soil.

4. Soil Texture Kinds of soil particles give soil it’s texture.
The texture affects its capacity to retain moisture and it’s ability to support plants.

5. Soil Particles Particle Size Feels Gravel coarse Sand 2 - 0.05mm
larger than 2mm
coarse
Sand mm
gritty
Silt mm
like flour
Clay
smaller than 0.002
sticky when wet

6. Loam-
about the same amount of sand and silt, plus a smaller amount of clay; plants grow best in this kind. (40/40/20)
(~ 40% sand, 40% silt, 20% clay)
Soil Particles

7. Particles separate with largest at bottom
water

8. Soil triangle animation from NC State

9. Soil Triangle practice Find the soil texture that has-
1. 15% clay, 70% silt, 15 % sand ________
2. 20% clay, 30% silt, 50% sand _________
3. 80% clay, 10% silt, 10% sand _________

10. Characteristics used to judge soil quality
Water holding capacity
Water infiltration (how easily water goes through)

11. Characteristics used to judge soil quality
Aeration (how much air b/n soil particles)
Workability
Root penetration

12. Soil Types…fill in good, fair or poor
Soil texture type
Water infiltration
Water holding capacity
Aeration
Workability
Root Penetration
Sand
Silt
Clay
Loam

13. Soil Types Soil texture type Water infiltration Water holding capacity
Aeration
Workability
Root Penetration
Sand
Good
Poor
Silt
Fair
Clay
Loam

14. Soil profiles: different layers of soil.
Each layer is called a horizon.
3 horizons labeled A, B, C
(*O horizon is leaf litter)
Parent rock

15. O A B C

16. Soil Horizons A horizon is the top layer of soil.
Dark color containing sediments, decayed leaves, the roots of plants, insects and worms.
Has changed the MOST since it was weathered rock
Has more humus and smaller sediments than other horizons
Humus- dark colored organic matter made of pieces of decaying plants and animals.

17. B horizon is the second layer
It is lighter in color, less evolved
Has little or no humus, some plant roots reach to this layer.
Contains minerals that were washed down from horizon A in a process called leaching.
Leaching- minerals are dissolved in water and carried down in a soil profile (kind of like
how a coffee maker works).
Davidson, Saskatchewan, Canada

18. Leaching is similar….

19. Leaching of the mineral chalcopyrite (CuFeS2)
precipitated as a mixture of:
chrysocolla (light blue copper silicate)
malachite (green copper-carbonate-sulfate).
iron (rust-brown)

20. C horizon is the bottom layer (residual soil)
Some material is leached from horizon B
No humus
Partly weathered rock
What is underneath horizon C?
Solid rock/parent rock

21. Are all soil profiles the same? NO!
Typical Soil profile in NC –
Surface layer:  dark gray sandy loam  Subsoil:  red clay and clay loam
Cecil soils occur on 1,601,740 acres in the State nearly one-third of the Piedmont Plateau in the Eastern United States. About half of the acreage of these soils is cultivated, and the rest is used for pasture or forest. The most common crops are small grain, corn, cotton, and tobacco.
The Cecil series consists of very deep, well-drained, moderately permeable soils on upland ridges and side slopes.

22. Are all soil profiles the same?
NO! The thickness and the soil composition depend on the climate and the type of rock the soil evolved from.
Other factors
Slope of land, amount of humus, length of time.
Ex. Soil in cold, dry climates has thin horizons b/c weathering is slower.
*It can take hundreds of years for 1 cm of soil to form.

23. Dust Bowl video

24. Soil Lossw/Video “dust bowl”
Overgrazing, poor farming practices and drought caused tons
of topsoil to be lost.
Desertification….
formation of deserts
3 human activities:
Overgrazing, growing crops in the same place, deforestation
Photo by Dorothea Lange