CCA Nutrient Management 3 — Questions and Answers
Question 1: A corn crop yielding 200 bu/acre removes approximately how many pounds of nitrogen in the grain?
- 80 lbs N/acre
- 120 lbs N/acre
- 160 lbs N/acre (Correct answer)
- 200 lbs N/acre
Correct answer: 160 lbs N/acre
Corn grain contains roughly 0.8 lb N per bushel, so 200 bu × 0.8 = 160 lbs N removed in grain at harvest.
Question 2: Denitrification is most likely to accelerate under which combination of conditions?
- Cool, dry, well-aerated soil
- Warm, saturated soil with available carbon (Correct answer)
- Cold, flooded soil with low organic matter
- Warm, dry soil at field capacity
Correct answer: Warm, saturated soil with available carbon
Denitrifying bacteria thrive when soils are warm, anaerobic (saturated), and have readily available carbon as an energy source.
Question 3: Which phosphorus soil test method is most widely recommended for soils with neutral to alkaline pH in western U.S. states?
- Mehlich-3
- Bray P-1
- Olsen (NaHCO₃) (Correct answer)
- Morgan
Correct answer: Olsen (NaHCO₃)
The Olsen bicarbonate method is preferred for neutral to calcareous soils because Bray P-1 acid extraction underestimates available P at high pH.
Question 4: The primary function of boron in plants is related to:
- Chlorophyll synthesis and photosynthesis
- Cell wall formation and structural integrity (Correct answer)
- Protein synthesis and nitrogen fixation
- Enzyme activation in starch metabolism
Correct answer: Cell wall formation and structural integrity
Boron is essential for cell wall cross-linking, pollen germination, and sugar transport, making it critical to structural development.
Question 5: When computing a nitrogen budget using the maximum return to nitrogen (MRTN) approach, the primary economic inputs are:
- Soil organic matter percentage and clay content
- Corn price and nitrogen fertilizer cost (Correct answer)
- Yield goal and previous crop type only
- Soil nitrate test and irrigation history
Correct answer: Corn price and nitrogen fertilizer cost
MRTN calculations identify the N rate that maximizes profit by comparing the cost of N fertilizer against the value of the resulting yield response.
Question 6: Which form of nitrogen fertilizer has the highest potential for ammonia volatilization when surface applied without incorporation?
- Ammonium nitrate (AN)
- Urea (Correct answer)
- Urea-ammonium nitrate (UAN)
- Ammonium sulfate
Correct answer: Urea
Urea is rapidly hydrolyzed by urease to ammonium carbonate, which readily loses NH₃ gas at warm temperatures and high soil pH when not incorporated.
Question 7: Iron chlorosis in soybeans on high-pH calcareous soils is best described as a deficiency of:
- Total iron in the soil
- Plant-available iron due to limited solubility at high pH (Correct answer)
- Iron in the atmosphere surrounding roots
- Iron fixed by soil microorganisms
Correct answer: Plant-available iron due to limited solubility at high pH
Calcareous soils contain ample total iron but at pH above 7.5 Fe³⁺ solubility drops dramatically, making it unavailable for plant uptake.
CCA Nutrient Management 3
A corn crop yielding 200 bu/acre removes approximately how many pounds of nitrogen in the grain?