2203 AGRN - Soil Science Exam III Tuesday, April 18, 2000
Your Name____________________________ TA_________________________________
1. All of the following are aspects of the "phosphorus problem" in soil fertility except: _____ a) the total phosphorus level of soils is low. b) much of the phosphorus in soils is insoluble and not available to plants. c) phosphorus compounds are highly volatile and are readily lost from soils through volatilization. d) the P in soluble phosphorus fertilizers is "fixed", or converted into insoluble forms, when P fertilizers are added to the soil. e) none of the above. 2. Nematodes are an example of soil: _____ a) microflora. b) fungi.
c) bacteria.
d) microfauna.
e) macrofauna.
3. When the phosphorus fixation capacity of a soil has been exceeded: _____ a) crops growing on the soil are likely to exhibit P deficiency symptoms. b) runoff from the soil is likely to contain elevated levels of soluble P. c) the P in added fertilizers will be rapidly fixed. d) the soil pH will drop rapidly. e) the soil will become anaerobic. 4. Riparian buffer strips are effective in: _____ a) preventing nutrients and sediment contained in runoff from entering streams and lakes. b) moderating soil pH. c) reducing concentrations of subsoil aluminum. d) reducing ammonia volatilization from soils. e) increasing the rate at which organic phosphorus is mineralized. f) all of the above. 5. Probably the most important function of soil organisms is: _____ a) moderating soil temperature. b) production of molecular oxygen.. c) production of methane and hydrogen sulfide. d) decomposition of organic residues. e) accumulation and subsequent detoxification of metals such as cadmium, nickel,and chromium. 6. The formal oxidation state of N in NO3- is: _____ a) -5. b) -3. c) 0. d) +3. e) +5. f) none of the above.
7. All of the following would tend to reduce the amount of nitrate lost from a soil through leaching except: _____ a) applying N fertilizer in several smaller splits instead of all at once. b) raising the pH by liming. c) seeding the soil in the fall to a non-leguminous winter cover crop. d) use of a nitrification inhibitor. e) none of the above. 8. The group of soil organisms that is primarily responsible for catalyzing the redox reactions of such elements as N, Fe, Mn and S in soils is the: _____ a) nematodes. b) actinomycetes. c) bacteria. d) earth worms. e) fungi. 9. One of the most ecologically and economically important activities of soil fungi is a symbiotic association with the roots of higher plants called: _____ a) rhizosphere. b) mycorrhizae. c) nodulation. d) parasitism. e) exudate. 10. Which of the following statements about organic nutrient sources (such as sewage sludge) is not true?: _____ a) Most of the N in organic sources is not immediately available to plants. b) The nutrient and moisture contents of organic nutrient sources are highly variable. c) The rates at which organic nutrient sources are applied are generally based on the N requirement of the crop being fertilized. d) Most of the N in organic sources is in the ammonium and nitrate forms. e) Assuming the same crop is being grown, the required application rate of organic nutrient sources decreases in the second year compared to that required in the first year. 11. Which of the following is more likely to occur in an anaerobic soil than in an aerobic soil? _____ a) nitrification. b) nitrate leaching. c) denitrification. d) ammonium fixation. e) mineralization. 12. Because of its size, the ammonium ion (and potassium, also) can become entrapped, or fixed, in the inner layer spaces of: _____ a) goethite. b) vermiculite.
c) kaolinite. d) Fe & Al oxides. e) humic acid. 13. Which of the following does not result in a loss of N from the soil? _____ a) denitrification. b) nitrate leaching. c) erosion. d) ammonia volatilization. e) immobilization.. 14. At low pH (below 6.0) phosphorus tends to form insoluble compounds with: _____ a) Al and Fe. b) Ca and Mg c) N and K. d) Cd and Ni.
15. The form of phosphorus that is taken up by plants is: _____ a) organic P. b) phosphate ion, H2PO4-. c) cyclic polyphosphate. d) adenosine triphosphate, ATP. e) Ca(H2PO4)2, triple superphosphate. 16. One of the major advantages of composting of animal manures is: _____ a) it results in a product that is easier to store and transport. b) no N is lost from the manure during or following composting. c) it increases the P content of the manure 10-fold. d) a composted product typically costs less than the raw manure. e) all of the above. 17. Anhydrous ammonia is most efficiently (and most safely) applied by: _____ a) broadcasting onto the soil surface. b) subsoiling. c) buttering. d) mixing with irrigation water. e) injection into the soil. 18. von Liebig's "Law of the Minimum" states that: _____ a) the smallest amount possible of fertilizer should be used. b) manures having very wide N:P ratios should be avoided. c) plant growth will be limited by that growth factor which is present in the lowest amount relative to its optimum amount. d) crop yields are limited by the rate at which N and P are made available for plant uptake through mineralization. e) none of the above.
19. The designation "13-13-13" is referred to as a fertilizer's: _____ a) ratio. b) proportion. c) margin. d) grade.
e) fineness.
20. The highest phosphorus fixation capacities are found in soils in the order: a) Vertisols. b) Mollisols. c) Alfisols. d) Oxisols. 21. The three steps in soil testing are: _____ a) hauling, spreading, and incorporating. b) analysis, formulation, and manufacture. c) weighing, extracting, and analysis. d) preparation, sampling, and interpretation. e) none of the above.
e) Histosols.
22. Biological nitrogen fixation: a) is a mechanism by which N is lost from the soil. b) is carried out primarily by soil fungi. c) is the process by which atmospheric N2 is converted into a form usable by plants. d) is the process by which some forms of N become trapped in the interlayer spaces of some types of clay minerals. e) is carried out primarily by soil actinomycetes. 23. Organisms which use organic carbon compounds for their carbon source are called: a) nitrogen-limited. b) autotrophs. c) fungal symbionts. d) facultative anaerobes. e) heterotrophs. f) none of the above. 24. Denitrification involves: a) the oxidation of ammonium to nitrate. b) the reduction of nitrate to N2 and N2O. c) the reduction of ammonium to organic-N. d) the oxidation of nitrate to N2 and N2O. e) the loss of NH3 from the soil. 25. The process whereby plant-available N and P are converted into organic forms residing in the soil biomass is refered to as: a) immobilization. b) mineralization. c) fixation. d) volatilization. e) polymerization.
Short Answer (17 pts.) 1. Describe how you should go about acquiring a representative soil sample from a 10 m by 10 m home garden. (3 pts)
2. Describe the University of Georgia's "nematode smasher", explain how it was used, and comment on its effectiveness. (3 pts)
3. List and discuss both the advantages and disadvantages of using crop rotations as compared to monoculture farming. (3 pts)
4. What is the rhizosphere, and in what ways does the soil in the rhizosphere differ from the rest of the soil? (3 pts)
5. A total of 300 kg/ha of nitrogen was supplied through animal manure and chemical fertilizer to a corn crop, but only 200 kg/ha was found in the harvested silage corn, all of which was removed from the land. What may have happened to the other 100 kg N/ha not taken up by the corn crop? (5 pts)
Hillel (8 pts.) Answer ANY TWO of the following five questions. (4 points each) 1. Why has the famous "Green Revolution", which worked wonders in helping Asian countries to boost grain yields and to overcome hunger during the last four decades, apparently failed in Africa?
2. According to Hillel, the cause of desertification is widely (and incorrectly) assumed to be the spontaneous expansion of deserts. What is a more accurate explanation for the actual cause of desertification?
3. Describe the socioeconomic and political factors which led to the deforestation of western Brazil in the 1970's.
4. In the chapter entitled "Endangered Wetlands", Hillel laments the continued loss of wetlands throughout the world. What are some of the functions served by undisturbed wetland ecosystems?
5. One of the Great ecological disasters of the twentieth century occurred in what used to be Soviet Central Asia in the area around the Aral Sea. Describe what happened here. Problems (25 pts.) 1. Calculate the fertilizer grade of pure diammonium phosphate, (NH4)2HPO4. (6 pts.)
2. How many pounds of actual K are there in a 100 lb bag of fertilizer labelled 20-18-16? (4 pts)
3. The average organic matter (OM) content of the top 15 cm of a soil is 4.25%. Assuming that the annual mineralization rate of the soil OM is 2.5%, that soil OM contains approximately 5% N by weight, and that a hectare-furrow-slice of soil weighs about 2 million kg, estimate the quantity (kg) of N
mineralized in a hfs of this soil in one year. (5 pts)
4. Lime-stabilized, aerobically digested sewage sludge containing 2.6% total N and 0.3% inorganic N (dry weight basis) is used to meet the annual N requirement of a crop of fescue hay, which is 170 kg N/ha. a) Assuming negligible N mineralization from the soil organic matter and 40% mineralization of the sludge in year 1, calculate the required application rate of the sludge in year 1. (5 pts.)
b) Using the same sludge and N requirement and assuming a second year mineralization rate of 12%, calculate the required application rate of the sludge in year 2. (5 pts.)