Homework #2
1. How do allophane, hydrous oxide, and layer silicate clay minerals differ from each other?
2. What is the source of negative charge on the humus fraction of the soil?
3. What are the dominant adsorbed cations in arid region soils? In Humid region soils?
4. What is the relationship between tetrahedral and octahedral sheets and layers?
5. What is the relationship between a unit layer of a clay mineral and a crystal or micelle of the clay?
6. What is the interlayer region of a silicate clay?
7. What is isomorphic substitution and why is it important to the properties of silicate clay minerals?
8. What is the most prominent member of the 1:1 crystal lattice type mineral group?
9. What is the force responsible for holding the unit layers of the 1:1 minerals together?
10. Why are the 1:1 lattice type minerals referred to as being fixed lattice types?
11. What is the degree of isomorphic substitution and interlayer activity in the 1:1 lattice minerals?
12. Why do the smectite minerals have such a large degree of shrink-swell?
13. Compare the amount of internal surface area and degree of shrink-swell in the 1:1, smectite and illite groups of clay minerals.
14. Compare the 1:1, smectite and illite groups of clay minerals with respect to their source and magnitude of negative charge.
15. Why does illite have such a limited capability of swelling compared to the smectites?
16. What is meant by clay minerals being interstratified or mixed layer?
17. What types of clay minerals result from a small degree of weathering and which minerals generally result from more intense or long-term weathering in the soil?
18. How does a change in soil pH value influence the magnitude of the negative charge on the soil colloids? How is the magnitude of the change in charge related to the mineralogy of the soil?
19. What is the mechanism by which the surface charge on soil particles is altered by a change in pH?
20. Explain how a soil colloid might take on a positive charge and the condition necessary for this to happen.
21. Write the balanced chemical reactions for the cation exchange reactions involving the replacement of Ca+2 by Na+ and replacement of Al+3 by K+.
22. Why is the cation exchange capacity of a soil expressed in cmolc/kg rather than on a weight/weight basis?
23. How many grams of H+ is equivalent to one mole of charge? How many grams of Na+? Mg+2?
24. If a soil contains 2 cmolc/kg of exchangeable K+:
a. how much K+ does it contain in grams of K+ per kilogram of soil?
b. How much KCl in grams per kilogram of soil and pounds per acre foot would it require to add this amount of K+ to a soil?
25. What is the approximate cation exchange capacity of a soil that contains 4% organic matter, 15% illite or fine-grained mica, and 50% Fe and Al oxide clays?
26. What is the relationship between the acidity of a soil and the amount of exchangeable Al?
27. How does Al+3 in soils influence the acidity of the soil solution?
28. Compare the behavior of Al and soil acidity in moderately acid soils to strongly acid soils? How does this influence plant response to the soil acidity?
29. What is the difference between active and exchange acidity? Which one is evaluated by measuring the pH of the soil?
30. How are soil pH and acidity related to the base saturation percentage of the soil?
31. Compare the base saturation and pH values of highly leached acid sols to arid zone soils.
32. If a soil has a cation exchange capacity of 18 cmolc/kg and a base saturation of 40%, how much exchangeable acidity does it contain in cmolc/kg? How many total exchangeable bases?
33. What is soil buffer capacity and how is it related to active and exchangeable acidity?
34. What soil components have the greatest influence on the degree of soil buffering?
35. Outline the process by which acid soils are formed from neutral parent materials.
36. What are three sources of acidity for the formation of acid soils?
37. How can human activity influence the magnitude of soil acidity?
38. How does the addition of ferrous sulfate, FeSO4, to a soil influence the properties of the soil?
39. Why is lime added to soils?
40. Name and write the chemical formula for three different liming materials
i.
ii.
iii.
41. What is the difference between calcite and dolomite limestones? Why are they often used as a mixture for liming of soil?
42. What does it mean to say that a liming material has a calcium carbonate equivalent of 66%?
43. Write the chemical reactions for what occurs as liming materials react with soil air and with soil particles.
44. How does liming of the soil influence pH, base saturation percentage and Al status of the soil?
45. If a soil has a cation exchange capacity of 22 comlc/kg and a base saturation percentage of 30, how much lime in grams per 5000 gram pot of soil and tons per acre-foot would it require to raise the base saturation to 90%?
46. What is the difference between saline and sodic soils?
47. Why is gypsum sometimes added to salt-affected soils?
48. Why is a high degree of salinity undesirable for the use of soils?
49. How is flocculation-dispersion of a soil related to its sodicity and salinity? Which combination of factors results in the greatest and least dispersion?
50. What kind of salt-affected soil can be improved by leaching with good quality irrigation water and which kind of soil will be made worse by leaching?