General Soils

Quiz 3 Study questions

1. Name and describe four types of soil colloids.

2. Draw a 1:1 and 2:1 type mineral. List the important characteristics of each.

3. Explain isomorphic substitution and how it influences the properties of a mineral.

4. Explain the differences between mica and montmorillonite.

5. Fill in the following table.

Colloid	Charge (cmol/kg)
Kaolinite
Smectite (montmorillonite)
Mica
Organic matter

6. What are the two types of charge on soil colloids?

7. The following concentrations of ions were removed from the exchange sites of a soil:

Ca = 3 cmol₊/kg

Mg = 2 cmol₊/kg

Na = 1.8 cmol₊/kg

K = 1 cmol₊/kg

Al = 1.5 cmol₊/kg

H = 1 cmol₊/kg

a. What is the cation exchange capacity of this soil?

b. What is the percent base saturation?

c. Is this soil a sodic soil?

8. What is the difference between active and exchangeable acidity?

9. What is the relationship between base saturation and pH?

10. What is meant by soil “buffering”?

11. How many kg of pure CaCO₃ are required to raise the pH of a ha-15cm of soil (D_B = 1.33 Mg/m³) from pH 5 (%BS = 40) to pH 7 (%BS=90). The total CEC of the soil is 20 cmol+/kg.

12. How many kg of pure CaCO₃ are required to completely replace the exchangeable acidity of a ha-15cm of soil with base saturation of 50% and a CEC of 25 cmol+/kg?

13. Explain “natural” acidifying processes and “human induced” acidifying processes.

14. What are two differences between the exchangeable sodium percentage and the sodium adsorption ratio?

15. Why are sodic soils problematic? How would you reclaim sodic soils?

16. Provide three reasons why people lime acid soils.