Name_______________________

Choose the one best answer (2 points each).

___ 1. Keeping a micronutrient in solution and available to plants by forming an organic complex around the micronutrient is called:

a. chemisorption of the cation with soil organic matter

b. chelation

c. adsorption

d. substitution of one ion for another

___2. Non-exchangeable K is:

a. K+ in soil solution

b. K+ held by negative charges on the surface of clays

c. Hydrated K+ between the expanded layers of 2:1 clays

d. K fixed between the lattice layers of clay minerals

____3. Why do some microorganisms reduce NO₃ and other molecules when oxygen is depleted after a soil is flooded for extended periods?

a. These organisms switch from oxygen to another electron acceptor in order to gain energy to carry out their cellular processes.

b. To release N₂ to the atmosphere to lower N in soils to levels acceptable for microbial activity under anaerobic conditions.

c. To supply nutrients to plants that grow under flooded conditions.

d. To maintain pH in soil.

___4. Which of the following reactions has been shown to cause toxicity to plants, in western Oregon during the wet winter and early spring on poorly drained, acid soils?

a. precipitation of Fe as Fe3+

b. Mn ⁴⁺Mn ²⁺

c. Formation of H₂S

d. Fe³⁺Fe²⁺

___5.Besides plant uptake, what is one major fate of sulfate fertilizer added to aerobic soils?

a. immobilized in the soil organic matter as sulfides

b. immobilized in the soil as ester sulfates, C-bonded S and other organic fractions

c. immobilized as sulfate

d. volatilized as H₂S

Match nutrient on left with its corresponding situation where it is most likely to have a deficiency in soils for plant uptake (answers on right may be used for several nutrients but only one letter is entered on left).

___6. K	a. Cool moist soil temperatures
___7. Fe	b. Acid soil
___8. S	c. Low organic matter/coarse textured soils
___9. Cu	d. High organic matter soils with neutral to alkaline pH
___10. Mo

11. (7) There has been a spill that contaminated the soil with Cu at levels that are unacceptable to the Oregon Department of Environmental Quality. The soil is well drained with relatively low amounts of organic matter (<2.0 %) and has pH of 5.1. Provide two soil management approaches you might follow to reduce the toxicity from Cu to acceptable levels. Provide chemical mechanisms that would be operating for each approach

12. (8) Sulfate is measured for the S soil test and it is not a very reliable test. Explain the limitations of the S test and why it can be unreliable. Conversely, explain why it does have some potential to be used in semi-arid regions and/or sandy/low organic matter soils.

13. (5) (extra credit) Grass tetany is caused by a soils related problem that affects feed quality and ultimately causes a nutrient deficiency in livestock. Which nutrient deficiency causes grass tetany and besides supplementing the nutrient in feed, how can one manage the soil to eliminate grass tetany.