Describe one important interaction between plant roots and nutrients in the rhizosphere.

Final Exam, SOIL515, Winter 2019

Instructions: Answer 7 out of the 10 questions below.  Keep your answers concise and focused.  All questions can be answered in less than half a page.    All questions count equally (there is no weighting of question “value”).   This file is in Word format. Please retain the text of the full question at the top of each answer.

Submit your answers by 5 pm Pacific time on Wednesday March 20 via email to me at    I will send you an email confirmation, saying that I received your test by Thursday, March 21, 6 pm.    

1. Describe one important interaction between plant roots and nutrients in the rhizosphere.  Describe the 1) “mechanism” of the interaction (how it works) from a biological/chemical or other science-based perspective, 2) what nutrients are typically involved in the interaction, and 3) possible positive or negative effects of the interaction on the plant’s ability to acquire nutrients from the soil.   Describe one case-study where this rhizosphere interaction has been demonstrated to be important in relation to crop production.

2.  You are producing sweet corn in the Willamette Valley (western Oregon).  You plan to change from conventional production to “organic” production.  Describe your new “organic” system in terms of nitrogen management.  Outline the rate, source, placement, and timing of N inputs in your new “organic” management system, and how the success of your new management system will be monitored.  

3. You are managing a sprinkler-irrigated farm for mixed vegetable crop production.   Soil is deep, with uniform loamy sand texture throughout the soil profile.  Vegetable crops produced in rotation include potatoes and broccoli.    The current soil pH (0-12 inch depth) is 5.5.  Outline a plan to maintain soil pH that is favorable for all crops in rotation.  Include brief description of soil sampling methods and soil tests that are needed to make decisions about pH management.  What soil amendments will be applied to manage soil pH, and how often are pH amendments applied?  Describe how your choices for N and K inputs (organic or mineral fertilizer) will affect soil pH.

4. Compare and contrast phosphorus (P), calcium (Ca), and boron (B) as potential toxic elements to crops.  How likely are you to see a toxicity resulting from a fertilizer application from each of these nutrients?  How does the potential for nutrient toxicity affect recommended practices for nutrient placement and rate?  Provide a brief example illustrating your recommendation.   

5. You receive a soil test report from a laboratory that has developed a “unique” extraction methodology for P.   The lab has a large database of soil P test values, and reports soil test P as low, medium, high, very high and excess.  Your client (farmer) wants to know what P fertilizer rate to apply to a crop, based on a “low” P test value.  What is your recommendation to the client?  Explain your reasoning/rationale for your recommendation.

6. Describe the benefits and limitations of using organic N or mineral N inputs in crop production systems with respect to crop N use efficiency.   Which form of nitrogen (organic or mineral) will likely result in the most nitrate-N leached below the crop rooting zone?  Explain your reasoning (why organic N or mineral N is likely to have greatest N loss via leaching). 

7. A city government recently banned phosphorus fertilizer sales within the city limits.  The goal of the ban was to improve the water quality of the city’s lake, which has algae blooms each summer that are attributed to P excess in the water.  Composts are not banned by the city’s new regulation (ban).   Only chemical fertilizers that contain a fertilizer guarantee on the bag (like 11-48-0) are banned.  You have been hired as a nutrient management specialist to advise the city regarding best management practices to reduce P loss to the lake.   Do you support the city’s ban on P fertilizers?  Why or why not?  What other practices might the city advocate to reduce P inputs to the lake?  What is the scientific justification or reasoning that supports your recommendations?  

8. You are working with a new biomass crop.  The aboveground crop biomass will be harvested and removed from the field as biofuel.  Describe a general method for determining the economic value of nutrients lost via crop removal.  Provide a numerical example, demonstrating your approach.

9. You are a technical service representative for a company that has developed a new patented urease inhibitor compound for use with nitrogen fertilizer.  Briefly describe (i) a cropping system scenario (nitrogen source, rate, placement, timing) where you expect the urease inhibitor to provide substantial economic benefit to farmers, and (ii) describe a scenario where you expect the little or no economic benefit from the urease inhibitor to farmers. Provide specifics in your scenarios for crop, fertilizer placement and timing of fertilizer application.

10. An engineering company has developed a new sensor that can be installed in the field. The sensor will provide real-time values for nitrate-N concentration (mg/L) in soil solution via wireless communication. What information would you need to use the sensor to make recommendations for rate and timing of N fertilizer delivered via drip irrigation (fertigation)? Explain your answer.

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