1. Ch 5 - Soils Important effect of weathering for people!
Important area of study for geologists.
Objectives
What is soil.
Know soil horizons and characteristics.
Know 2 types of soils
Causes & preventions of soil erosion

2. What is Soil? Soil consists of: Regolith - minerals & rock fragments
Humus - organic matter
Gases
Water
Living organisms

3. How does soil form? Five factors influencing soil formation: Climate
Parent rock
Organisms
Plants
animals
Topography
Time

4. What is a soil profile?
A soil profile consists of several soil horizons.
O horizon
humus on the ground surface.
A horizon
Top soil.
Rich in organic matter. Typically dark color.
Also called zone of leaching.
B horizon
Subsoil.
Also called zone of accumulation.
May contain soluble minerals such as calcite in arid climates (caliche).
C horizon
Weathered bedrock (rotten rock).
Bedrock lies below the soil profile.

5. Soil Horizons – Field

6. Figure 6. 17

7. Major Soil Types Pedalfer Pedocal rich in Al and Fe.
form in humid climates
Pedocal
rich in Ca.
form in arid climates
commonly contain caliche (or hardpan), a calcium carbonate deposit which accumulates in the soil.

8. US Soil map Gray-brown & moist Soft & organic rich
Strongly weathered & clay rich

9. Soil Orders

10. Have you ever had your soil analyzed?
This can be done by county extension office. Gives you information on:
pH of your soil.
Is your soil acidic or basic?
Elements - Plants require
P, K, Ca, Mg
B, Mn, Zn
Nitrates (fertilizer) –
N, P, K (in that order)
listed as weight percents
Ex or
Organic matter
Soluble salts

11. Particle Sizes
Loam

12. Loam – Combination of Sand, Silt, Clay
Soil's productivity is mainly due to the clays in the soils

13. Based on % of sand, silt, & clay
Names for Loams
Based on % of sand, silt, & clay

14. Soil erosion - (weathering & erosion are different).
Due to water (runoff) or wind.
transported by streams
deposited on floodplain or at mouth of river.
trapped behind dams
reduces beach sand
accelerate beach erosion.
Dust Bowl of the 1930's - due to wind erosion of soil following extended drought and over-tilling of the soil.

15. hectare = 10,000 square meters, or 2.471 acres
Slopes Make it Worse
1 % slope = 3 tons soil lost per hectare/yr
5 % slope = 87 tons lost per hectare/yr
At this rate a 15 cm thickness of topsoil would disappear in about 20 years,
15 % slope = 221 tons lost per hectare/yr
hectare = 10,000 square meters, or acres

16. How can we slow soil erosion?
Contour plowing
Terraces
Crop rotation
Planting groundcovers
Windbreaks
Reduce overgrazing