1. Weathering and Soils

2. Regolith-
The layer of weathered rock fragments beneath the soil and above the bedrock (solid rock).
← Soil
← Regolith
← Bedrock

3. Soil = minerals, water, gases, organic mtl.
Soil Components
Regolith is the basis for soil…
Soil = minerals, water, gases, organic mtl.

4. humus- dark, organic material made of decayed animal and plant remains
Found just beneath the vegetation
Important part of soil- provides nutrients!
← Humus

5. 3 types of rock materials make up soil- classified by the size of the particles.
Sand (0.05 – 2 mm in dia.)
Silt (0.002 to 0.05 mm)
Clay (<0.002 mm in dia.)
The amounts of each of these components depends on the parent rock!

6. Soil Facts Lichens-die add organic nutrients to soil
Slowly renewable resource- 1cm=15 or more years
Filters water-infiltrationleaching (diluting nutrient rich layers) into aquifers/surface runoff
Decomposer
Carbon Sink
Biogeochemical Cycles!!!
PROBLEM: Erosion

7. Soil Triangle and Example

8. Clay soils- high percentage of clay
Come from rocks with a lot of feldspar…
Hold a lot of water
Doesn’t drain well

9. Silty soils Very fine particles, have a gritty feel Erodes easily
Often found on riverbanks

10. Sandy soils- high percentage of sand
Come from weathered granite and rocks with a lot of quartz
Doesn’t hold water, drains quickly

11. Transported vs. Residual soil
Transported soil = moved from original location, will have a different composition than the bedrock below
Residual soil = soil that rests on top of its parent rock

12. Soil profile
Cross-section of layers of soil and the bedrock
beneath

13. Horizons (Residual Soil)
A horizon – topsoil
B horizon – subsoil (minerals, clay, humus)
C horizon – partially weathered bedrock (regolith)
O- Organic
E- no organics
R- bedrock
Top 2 layers-bacteria, fungi, worms, insects

14. Transported soils DO NOT have horizons, they are found in layers or unsorted depending on how they were transported!

15. Soil and Climate
Humid tropical climates: a lot of rain + high temps = chemical weathering
Desert climates: minimal rain, high temps= minimal weathering
Temperate climates: temperature range between cool and warm, rainfall varies = both types of weathering

16. Tropical Soils
Laterites – Thick but infertile soils produced in tropical climates
Contains irons and other minerals that do not dissolve
Topsoil often thin
Organic matter
constantly added

17. Desert Soils
Thin
Made up of mostly rock fragments (evidence of mechanical weathering)
Arctic soil similar

18. Temperate Soils
All three horizons can reach a thickness of several meters.
2 main types:
1. pedalfer- contains clay, quartz, and iron compounds, forms in places receiving 65cm + of rain per year (Ex. states east of Mississippi and Gulf Coast states)

20. 2. pedocal- contains large amounts of calcium carbonate, formed in places receiving less than 65 cm of rain per year.

21. Soil types around the world correspond to climates…

22. Topography and Soil Too flat = poor drainage
On slopes- soil is thick and fertile at the bottom and thin and nutrient-poor on the slope.
Ideal soil conditions = fairly flat but with good drainage