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Exam 1. (25 points) Consider the following soils, as classified by U.S. Soil
Taxonomy:
Typic Pellustert, clayey, smectitic, isohyperthermic
Typic Acrudox, clayey, kaolinitic, isohyperthermic
Typic Calciorthid, loamy, carbonatic, isothermic
Typic Kandiustalf, loamy, mixed, isohyperthermic
Answer the subset of questions (a. to f.) based on these soils. To obtain
credit, briefly explain your reasoning for each answer. If you need
to make assumptions then state them clearly.
a. (4 points) On which soil(s) is corn production possible without irrigation?
b. (4 points) When under native conditions which soils would have rainforest vegetation and which would have savanna vegetation?
c. (5 points) Rank these soils in terms of leaching potential from highest to lowest.
d. (4 points) Which soil would have the most and least potential for physical problems from tillage in a continuous cropping system?
e. (4 points) Which soil should have the highest effective cation exchange capacity?
f. (4 points) Assuming they are on similar landscape positions and have similar groundcover, rank these soils in terms of potential % of rainfall lost as runnoff from highest to lowest.
2. (25 points) A farmer on an Ultisol in a udic soil moisture regime grows
two crops per year, corn and peanut. He/she has limited resources but has
heard about using mulches from compost of crop residues. She/he wants your
advice on its potential application to hers/his cropping system.
a. (15 points) What would be some positive factors you would mention about
compost mulches?
b. (10 points) What would be some negative factors you would mention about compost mulches?
3. (25 points) Consider the following corn yield response curves to fertilizer N on soils A and B. Calculate the apparent fertilizer N recovery for each soil when applying 100 kg N ha-1. Assume an internal N concentration of 1.0% in aboveground biomass and a grain:stover ration of 1.0. No credit will be provided for a correct answer unless you include your calculations.
4. (25 points) The following data is for three soils in an
ustic soil moisture regime. Corn, with a critical Al saturation of 30%,
will be planted on all soils.
| SOIL | pH in | EXTRACTED IN UNBUFFERED SALT | CEC at | |||
|---|---|---|---|---|---|---|
| WATER | Ca | Mg | K | Al | pH 7 | |
| cmol kg-1 soil | ||||||
| A | 4.3 | 0.1 | 0.1 | 0.1 | 1.2 | 2.3 |
| B | 5.8 | 0.6 | 0.5 | 0.1 | 1.8 | 3.5 |
| C | 5.0 | 1.7 | 1.4 | 0.2 | 2.2 | 5.3 |
a. (7 points) Which soil has a discrepancy in the data which makes it questionable whether it is correct? What is the discrepancy?
b. (9 points) Rank the soils in terms of the amount of lime required from highest to lowest.
c. (9 points) Which soil will have the greatest percent increase in negative charge after liming?
1. (25 points) In class we discussed how increasing clay content tends to a) decrease critical soil test P levels for a particular crop, and b) increase P adsorption or fixation by the soil. This would appear to be a discrepancy. Explain why it is not.
2. (25 points) You are asked to develop a P fertilization program for a region under the condition that only phosphate rock can be used. Other than information normally required for soluble fertilizer P, what other information would you need to develop such a program? Explain why each item would be needed.
3. (25 points) Discuss how N fertilizer requirements and management differ between paddy (lowland irrigated) and upland rice systems.
4. Consider the figure on the next page as a simplified model of the nutrient
cycle in a tropical forest.
a. (12.5 points) Explain how the inputs and outputs from the system would
change after one year of annual crop cultivation and slash and burn clearing.
b. (12.5 points) Explain how the internal cycling between soil and vegetation pools would change after slash and burn clearing and one year of cultivation with annual crops.
1. (25 points) For each land use option discussed during the course, we have considered adapting species and cultivars to local conditions (rather than modifying soils to meet the plant's requirements. Describe how this plant adaptation process for animal production in grass-legume pasture associations differs from other land use options.
2. (25 points) In humid tropical regions soil fertility dynamics (changes with time) under pastures are quite different than under annual cropping systems. Initial soil properties and land clearing practices, however, appear to be the same under both systems. What are some of the reasons for such differences?
3. (25 points) Consider tree plantation systems where tropical rainforests are cleared and trees are grown through several rotations. List what you believe to be the most critical phases of the production system for on-site nutrient conservation. Explain why these tree crop production phases would be critical.
4. (25 points) Poor annual crop yield for alley cropping systems in acid soils led the authors of a recent review to state that "the desirability of alley cropping on humid tropical acid soils has not been conclusively proven, except for the obvious soil erosion control in steep slopes". List the system components which you feel should be improved and describe in what way they should be modified.
Last Modified on October 10, 2001