CCA Nutrient Management Planning 3 — Questions and Answers
Question 1: A nutrient management plan must account for manure application rates. A beef feedlot manure has 30 lbs total N per ton. If 50% of the N is ammonium (NH4-N) with a volatilization loss of 25%, what is the plant-available N from ammonium per ton of manure?
- 7.5 lbs/ton
- 11.25 lbs/ton (Correct answer)
- 15 lbs/ton
- 22.5 lbs/ton
Correct answer: 11.25 lbs/ton
Ammonium-N = 15 lbs/ton × (1 − 0.25 loss) = 11.25 lbs/ton available from the ammonium fraction.
Question 2: The term 'luxury consumption' of potassium by crops refers to:
- Crop uptake of K above amounts needed for maximum yield when soil K is high (Correct answer)
- Excessive K fertilizer application that causes soil K to exceed crop removal
- Potassium fixation in clay minerals that makes it unavailable to plants
- The preferential uptake of K over competing cations at low soil pH
Correct answer: Crop uptake of K above amounts needed for maximum yield when soil K is high
Luxury consumption occurs when crops absorb K beyond their physiological requirements for maximum yield because soil K supply is abundant.
Question 3: A CCA is planning nitrogen applications for irrigated corn in a semi-arid region. Which of the following is the BEST strategy to minimize nitrate leaching while maintaining yield?
- Apply all nitrogen as a pre-plant incorporation to ensure uniform distribution
- Split nitrogen applications timed to match crop uptake using fertigation (Correct answer)
- Use only slow-release nitrogen to eliminate leaching risk entirely
- Apply nitrogen in a single side-dress application at V6 growth stage
Correct answer: Split nitrogen applications timed to match crop uptake using fertigation
Fertigating N in split applications precisely timed to peak crop demand minimizes the N available for leaching during periods of low uptake.
Question 4: Which of the following represents the CORRECT order of cation adsorption strength on a negatively charged clay surface (weakest to strongest)?
- K+ < Ca2+ < Mg2+ < Al3+
- Na+ < K+ < Mg2+ < Ca2+ < Al3+ (Correct answer)
- Ca2+ < Mg2+ < K+ < Na+ < Al3+
- Al3+ < Ca2+ < Mg2+ < K+ < Na+
Correct answer: Na+ < K+ < Mg2+ < Ca2+ < Al3+
Adsorption strength increases with charge and decreases with ionic radius; Al3+ > Ca2+ > Mg2+ > K+ > Na+ is the lyotropic series for common soil cations.
Question 5: A nutrient management plan for a corn-soybean rotation includes organic matter decomposition credits. If a field has 3.5% organic matter, what approximate annual nitrogen credit (lbs N/ac) from mineralization is used in most Midwest state guidelines?
- 10–15 lbs N/ac
- 20–35 lbs N/ac (Correct answer)
- 40–60 lbs N/ac
- 70–100 lbs N/ac
Correct answer: 20–35 lbs N/ac
Most Midwest guidelines credit approximately 20 lbs N/ac per 1% organic matter annually, so 3.5% OM yields roughly 20–35 lbs N/ac from mineralization.
Question 6: Secondary macronutrient deficiency symptoms in crops often appear first on older leaves. Which of the following nutrients is MOST mobile in the phloem and therefore shows deficiency symptoms on older tissue?
- Calcium
- Sulfur
- Magnesium (Correct answer)
- Boron
Correct answer: Magnesium
Magnesium is highly mobile in the phloem and is reallocated from older to younger leaves under deficiency, causing interveinal chlorosis on lower leaves first.
Question 7: In a nutrient management plan, 'crop removal values' are used to estimate nutrient budgets. Which nutrient has the HIGHEST typical removal rate (lbs/bu) in corn grain?
- Nitrogen (Correct answer)
- Phosphorus (P2O5)
- Potassium (K2O)
- Sulfur
Correct answer: Nitrogen
Nitrogen removal in corn grain is approximately 0.67 lbs N/bu, substantially higher than P2O5 (0.37 lbs/bu) or K2O (0.27 lbs/bu) removal rates.
CCA Nutrient Management Planning 3
A nutrient management plan must account for manure application rates.
A beef feedlot manure has 30 lbs total N per ton.
If 50% of the N is ammonium (NH4-N) with a volatilization loss of 25%, what is the plant-available N from ammonium per ton of manure?