Soil Science 1
2nd Lecture Exams
2nd Semester, 1999-2000

I. True or False (write T or F)

1. Most of the clay particles are of colloidal size.
2. The very high specific surface area of soil colloids due to their fineness.
3. The silicate clays are inorganic colloids.
4. Colloids are the seat of chemical reactions in soils.
5. The basic structure of kaolinite crystal lattice is one layer of Si tetrahedron and one layer of AL octahedron.
6.  The montmorillonite crystal is 2:1 type of lattice.
7. The negative charges of organic soil colloids arise from OH and phenolic functional groups.
8. The negative charge kaolinite is manly pH-dependent.
9. As the pH increases, the negatice charges o organic colloids increase.
10.  The permanent charge of inorganic colloids like montmorillonite arise mainly from the isomorphous substitution.
11. Isomorphous substitution means the that cation of similar charge substitute for each other on the crystal structure.
12. Montmorillonite ia a 1:1 non expanding clay type.
13. Soil colloids acquire positive charges when thy attract hydroxyl (OH) ions at high pH.
14. Montmorillonite crystal lattices are bounded by strong oxygen bonds that make them non-expanding clay type.
15. Cation exchange capacity of soils is due to their positive charges.
16. The cation exhange reaction of colloids is stichiometric, that is, one gram of cation is exchange for one gram of another.
17. Soils dominated by Kaolionite have expanding and shrinking property.
18. Soils with high organic matter tend to have low CEC.
19. Sandy soils have higher CEC than clayey soils.
20. Soils which are saturated with Ka, Ca, and Mg have low pH.
21. Aluminum is an acid forming cation.
22. Soil pH is the relative concentration of H and OH ions.
23. Reserve acidity is due to the H ions adsorbed in soil colloids.
24. Buffering capacity is the ability of soils to resist drastic changes in pH.
25. Clayey soils have a higher buffering capacity than sandy soils.
26. Soil pH is an indicator if lime is needed but not how much lime is to be applied.
27. Percent base saturation is the relative concentration of  bases over the acid cations.
28. Soils may become acidic with  time due to leaching of bases.
29. Aluminum acidifies soils due to its hydrolysis.
30. High sodium saturation of soils causes dispersion of soil aggregates.
31. Calcium ions disperse soil colloids.
32. Soils with pH of 6.0 must always be limed to 6.5.
33. The finer the liming material, the less effective it is.
34. Calcium oxide has lower RNP than calcium carbonate.
35. Soil salinity may be corrected by limimg.
36. The most versatile or adaptable soil organisms which can live at any pH level are the bacteria.
37. Symbiotic nitrogen fixation is the conversion of atmospheric N to unavailable forms.
38. The fungi decompose the least resistant organic compounds like protein.
39. Bacteria act on the most easily decomposed compounds such as lignins, fats and waxes.
40. Aerobic bacteria are those which thrive even in the absence of oxygen.
41. Falcultative bacteria can live with or without oxygen.
42. Bacteria prosper at pH 6-7.
43. aerobic decomposition of organic matter yields carbon dioxide and energy.
44. Heterotropic bacteria derive C and energy from organic matter.
45. Nitrogen is lost as ammonia gas like alkaline soils.
46. Denitrification is attributed to anaerobic organisms in the paddy soils or poorly drained soils.
47. Mineralization of nitrogen from organic matter is done by soils organisms.
48. Nitrification of ammonium ions acidifies soils.
49. Nitrate nitrogen is easily lost through leaching.
50. Immobilization is the transformation of available N to organic N.

II. Problem Solving

    A soil sample was analyzed and found to contain the following amounts or exchangeable cations.                 

Calculate:

1. Cation exhange capacity
2. % base saturation
3. Exchangeable sodium percentage (ESP)
4. KgK⁺ contained in 1 HFS (2 x 10⁶ kg) given that atomic weight of  is 39.

Answers:

Part I.