Plant Sciences 508 Spring 2005
Sample Final Exam Questions
As with the midterm exam, you should study these questions carefully; if there are any where you are unclear on the answers, you should bring them up in class during the review for the exam, or contact me outside of class for clarification.
What is meant by density-dependent and density-independent mechanisms of population regulation? For insect pests of crops, identify the major causes of mortality and whether these operate in a density-dependent or density-independent manner. Which class of population-regulation mechanism is more effective and why?
What is the "Yurimaguas Technology" for improving agricultural systems in the tropics? What are some of the constraints to the application of this technology.
Given yields of two (or more) crops in monoculture and their intercrop, be able to calculate the relative yield total of the intercrop and answer the following questions: (a) does the intercrop overyield, and why?, (b) what is the dominant component of the intercrop, and why?
Vegetation (including weeds) adjacent to a field can harbor residual populations of an insect pest, yet still contribute significantly to the control of that pest--how is this possible?
What are the important direct and indirect ways that fossil fuels are used in agriculture in the US? What represents the largest single input of fossil fuel energy in (a) humid zones, such as the corn belt, and (b) arid zones, such as Arizona?
Discuss why many crop plants, in comparison to many wild species, are poorly defended against herbivory.
Critics of organic agriculture claim that yields on organic farms will resemble yields from 50 years ago prior to the adoption of inorganic fertilizers and synthetic pesticides. What is the correct way to evaluate yields of organic farms, and what do the research results show? What other changes have occurred since the 1940s that affect yields?
What are externalities? Give examples of significant externalities associated with (a) pesticide applications to agricultural fields, (b) fertilizer use in agriculture, and (c) soil erosion from agricultural fields.
Why is intercropping rarely practiced in developed nations of world, such as the US, Australia, or most European countries?
What factors are necessary for the development of resistance to an insecticide in an insect pest?
It is widely believed that the ash produced by fires in traditional, shifting agricultural tropical agroecosystems has a beneficial effect on soil fertility. Comment, and describe the overall effects of burning on nutrients in these systems.
Agroecologists recognize three levels of responses to problems with dependence on outside inputs in agriculture: (1) increased resource-use efficiency; (2) input substitution; and (3) system redesign. Given examples of each of these approaches to solving resource-supply problems in US agriculture.
Distinguish between therapeutic vs. preventative tactics for pest control. Which is the better manner of using insecticides, and why? Describe how a tactic like Bt toxins could be applied in a therapeutical vs. preventative manner. Which would be better, and why?
What is a cover crop? What are some of the agroecological advantages of cover-cropping? What are some of the disadvantages to using cover crops?
What physical and/or environmental factors contribute to soil erosion (as identified in the universal soil-loss equation)? What cropping and conservation practices can be used to reduce soil erosion rates?
Why have herbivorous insects developed resistance to insecticides much more rapidly than predaceous or parasitoid insects? That is, how do herbivorous insects cope with insecticides and why don't predators and parasitoids use the same mechanisms to an equal extent?
Contrast short rotations with long or extended rotations. What are the objectives of each type of rotation?
What is allelopathy? How might allelopathy be used in agriculture to improve weed control?
What is a secondary pest? What is meant by pest resurgence? How does insecticide use affect secondary-pest outbreaks and pest resurgence?
What is meant by the concept of an ecological niche? How does this concept help explain overyielding in intercrops where no facilitation is occurring?
What is meant by overyielding (in reference to intercrops), and how can it be measured? Define and contrast complementarity and compensation as competitive mechanisms for overyielding.
What are the suggested benefits of agroforestry systems in the tropics, and what are the agroecological mechanisms that might account for these benefits?
Define what is meant by: (a) qualitative vs. quantitative plant defenses; and (b) constitutive vs. inducible plant defenses. Give examples of each.
What is meant by the specific rotation effect? What are some of the potential causes of this rotation effect?
What is a smother crop? What are the characteristic that would make a species an effective smother crop? Give examples of smother crops used in the temperate zones.
Contrast the following aspects of intercrop design: (a) between row vs. within row intercrops; (b) additive vs. replacement intercrops; and (c) relay vs. simultaneous intercrops.
What are some of the possibilities for production of liquid fuels within the agricultural sector for on-farm use? For each type of fuel, identify (a) the process, and (b) the feedstocks used. What are the principal advantages and disadvantages of the various options? What are the tradeoffs involved in using crop residues as feedstocks for energy production?
Characterize highly weathered tropical soils (i.e., ultisols and oxisols) in terms of their (a) clay composition; (b) cation exchange capacity; (c) pH; and (d) aluminum status. What effects would liming have on these properties?
Describe the major historical changes in energy use on US farms during the 20th Century. What major technological advances were associated with each major change in energy use in agriculture. Has US agriculture become more or less efficient in terms of energy consumption (and why)?
What is meant by facilitation? What are some of the ways in which facilitation might occur in intercrops?
What is the theory of plant apparency? What does it predict about the nature of defenses in crop plants? In general, what factors are now believed to be most important in explaining herbivorous insect feeding strategies?
What is meant by a damage curve? Draw typical damage curves for relative crop yield versus (a) most insect pests, and (b) weed population densities. What accounts for the differences in shapes of these curves?
Intraspecific competition among plants is expected to be more severe than interspecific competition--explain why. What characteristics have been bred into crops to reduce intraspecific competition?
Herbicide use has increased greatly over the last 3 decades of the 20th Century, while insecticide use has tended to decline (at least in the US); what are some of the reasons for these trends?
Insecticide manufacturers strongly opposed efforts to reduce insecticide use during the 1950s and 1960s, yet are now some of the major advocates of integrated pest management--what factor(s) are responsible for this change in position?
Contrast vegetative and reproductive mimicry; what are the specific mechanisms that account for the increased fitness of crop mimics?
What are the basic approaches to estimating nitrogen fixation by legumes in crop rotations? Describe whether they tend to overestimate or underestimate BNF, and why.
URL: http://ag.arizona.edu/~spmcl/Sample508Final.htm
18 April 2005