Name: PLSOIL 105 & 106 First Hour Exam February 27, Part A. Place answers on bubble sheet. 2 pts. each.

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1 Name: PLSOIL 105 & 106 First Hour Exam February 27, 2012 Part A. Place answers on bubble sheet. 2 pts. each. 1. A soil with 15% clay and 20% sand would belong to what textural class? A. Clay C. Loamy sand E. Silt loam 2. Which one of the following ions will cause clay particles to flocculate (= to stick to each other)? A. Ca 2+ B. K + C. Na + D. NH + 4 E. Cl - 3. In soil science, topsoil is called the... A. A horizon. B. B horizon. C. C horizon. D. O horizon. E. R horizon. 4. What is the maximum effective diameter of a clay particle? A. 2 mm B mm C mm D mm E mm 5. What is the maximum effective diameter of a sand particle? A. 2 mm B mm C mm D mm E mm 6. The textural class of a soil may change if you destroy all the organic matter in it, since the organic matter usually affects the way the soil feels. 7. Stokes law states that the settling velocity of soil particles (V) is proportional to the square of D, which represents... A. the distance the soil particle has already fallen. B. the density of the soil particle. C. the density of the surrounding fluid. D. the diameter of the soil particle. 8. Soil containing mostly clay and very little sand or silt is likely to feel... A. Plastic or sticky (when wet) B. Scratchy C. Silky smooth (when dry)

2 9. To form soil structures like blocks or columns, a soil needs to contain a fair amount of what size of particles? A. Clay B. Gravel C. Grit D. Sand E. Silt 10. In which soil horizon do blocky and columnar structures usually occur? A. A horizon B. B horizon C. C horizon D. O horizon E. R horizon 11. It is usually easiest to pull weeds from a dry... y sand C. Loam D. Silty clay loam 12. If you plowed soils in the following textural classes to a depth of 7 inches, your tractor would have to work hardest (and you would use the most fuel per acre) in a... y sand C. Loam 13. Which soil s volume changes the least in response to equal forces of compaction? C. Sand 14. Which soil probably has the lowest dry bulk density if all three soils are as loose and as little compacted as possible? C. Sand 15. All other factors being equal, which soil will have higher CO 2 concentrations? A. Compacted soil B. Uncompacted soil 16. All other factors being equal, which soil will have higher CO 2 concentrations? A. Wet soil B. Dry soil 17. All other factors being equal, which soil will have higher CO 2 concentrations? A. Soil with manure added recently B. Manure-free soil 18. Which one of the following is NOT likely to result from the application of a thick layer of organic mulch? A. Soil will stay warmer into the autumn and over the winter. B. Soil will warm up more quickly in the spring. C. Soil erosion will be reduced. D. Weeds will be suppressed. 19. In winter, subsoil at a depth of 2 feet (60 cm) reaches its lowest temperature... A. a few weeks before topsoil at a depth of 4 inches (10 cm) does. B. a few weeks after topsoil at a depth of 4 inches (10 cm) does. C. at just about the same time as topsoil at a depth of 4 inches (10 cm) does. 20. At the end of the growing season, the soil in a regularly plowed agricultural field probably has higher bulk density than otherwise identical (except for human manipulation) soil in an adjacent wood lot that has not been plowed for 50 years.

3 21. If a loam is at the permanent wilting point, then... (Note: Choose only one.) A. No soil pores are filled with water. B. Some plant-available water remains in the soil. C. Moisture tension equals -a bar. D. Moisture tension equals -15 bars. E. Moisture tension equals -31 bars. 22. Saturation and Field capacity are synonyms. Both terms describe soil that is completely filled with water so that no air remains in any pore spaces. 23. That rate at which water flows through a thin tube of diameter D is proportional to what power of D, assuming all other factors (like tube length and pressure head) stay constant? A. D -1 B. D C. D 2 D. D 3 E. D Adding organic matter to a soil will generally... A. make it able to store more plant available water. B. make it able to store less plant available water. C. have no effect on the amount of plant available water the soil can store. 25. The same amount of irrigation water is applied to a clay loam soil and a loamy sand soil. After 4 hours, which one of the following will be true? A. The water will be infiltrating the two soils at approximately the same rate. B. The water will be infiltrating the clay loam faster than the loamy sand C. The water will be infiltrating the loamy sand faster than the clay loam. 26. At the permanent wilting point, which soil (usually) contains the most total water? C. Loamy sand E. Silt loam 27. Which soil (usually) can store the most plant available water? C. Loamy sand E. Silt loam 28. Which two atoms/ions are small enough to fit in the centers of tetrahedra in clay layers? A. Al and Ca 3+ + B. Al and K C. Al and Si D. Si and Ca 4+ + E. Si and K 29. In a 2:1 clay by definition,... A. there is twice as much oxygen as there is silicon. B. there is twice as much magnesium as silicon. C. there are two tetrahedral sheets per layer. D. there are two octahedral sheets per layer. 30. The holes in the centers of the octahedra in trioctahedral clay minerals are mostly 2+ filled with divalent cations like Mg. 31. Smectites have greater CEC (per g) than vermiculites.

4 32. Compared to vermiculites, smectites swell more when wetted and shrink more when dried. 33. Which one of the following clays has the most anion exchange capacity at ph = 4? A. Chlorite B. Fine micas C. Hydrous oxides of Fe and Al D. Smectites E. Vermiculites 34. Plants growing in compacted soils often have difficulty obtaining sufficient water in drying soil even before the soil reaches the permanent wilting point because the strength of the soil gets too high to allow good root penetration. 35. Which measure of the abundance of water in soil best approximates the way plants sense the availability of water? A. Gravimetric water content B. Volumetric water content C. Soil water potential (suction) 36. Which kind of soil structure is likely to be stabilized by organic matter? A. Blocks B. Prisms/columns C. Spheroidal aggregates 37. The attraction of water molecules for the walls of a glass capillary tube is an example of... A. adhesion. B. cohesion. 38. At 3:00 P.M. on a sunny day in July, which is likely to have the highest temperature? A. Air two inches above bare soil. B. Half of an inch down in the bare soil. C. One foot down in the bare soil. Part B - Short answers. For these questions, place your answers in words and/or numbers directly on this question booklet 39. Please list two materials of biological origin that help to stabilize spheroidal aggregates. (4 pts.)

5 3 A 91.4-cm sample of a loam is taken from the field three days after a long, soaking rain, when the soil was at field capacity. The field-moist weight of the soil was g, and the weight of the same sample after drying in an oven overnight was g.(3 pts. each for these problems.) 40. What was the percent gravimetric moisture content, or GMC, of the soil at field capacity (calculated according to the conventions usually followed in soil science)? 41. If this soil reaches the permanent wilting point at a gravimetric moisture content of 6.85%, how much plant available water can this soil store? 42. What is the dry bulk density (D b) of the soil? 43. What is the porosity of the soil as a percentage of total soil volume? Hint: It may help to -3 recall that %Porosity = [1 - (D /D )] 100, and that D is usually about 2.65 g cm. b p p 44. What is the volumetric moisture content (VMC) of the soil at field capacity? 3 Hint:VMC = GMC D (1 cm of water /g of water). (Either a fraction or % is O.K.) b 45. What fraction of the soil s porosity is filled with water at field capacity? 46. What is the name of the most abundant (dioctahedral) 1:1 clay on earth? (2 pts.)

6 47. As promised, here is the Extra-credit Question. Extra credit is available here for any information you learned for this exam that you have not already used in answering the first 46 questions. The first two points are especially easy to get, so PUT SOMETHING HERE! We will accept just about any not-previously-tested information, but here are some ideas to help you get started: In compacted soils, dry conditions are more of a problem than usual (cf., question 34). What s the big problem for plants in a compacted wet soil? Remember anything about how you should space irrigation ditches in fine- versus coarse-textured soils, and why? What is the approved term for the device your instructor was pleased to call a suckometer? What the heck is hysteresis? (Hint: It is not something that happens to students near the end of one of these soils exams.) What are the names of two young clays. What kind of layers do they have? What glues those layers together? As clays age, how do they change? You could answer the last question in terms of changes in CEC, changes in shrink/swell tendency, changes in Si content, or changes in the extent of isomorphous substitution. Which has more CEC: a gram of well-decomposed colloidal humus, or a gram of vermiculite?