CFA Nutrient Sources and Management 2 — Questions and Answers
Question 1: Which fertilizer material is considered an organic nitrogen source because it releases nitrogen through microbial decomposition?
- Urea
- Ammonium nitrate
- Feather meal (Correct answer)
- Calcium nitrate
Correct answer: Feather meal
Feather meal is an organic nitrogen source that releases nitrogen slowly as soil microbes break down the protein.
Question 2: A fertilizer label reads 10-20-10. What is the percentage of phosphate (P₂O₅) in this product?
- 10%
- 20% (Correct answer)
- 30%
- 40%
Correct answer: 20%
The second number in the N-P-K grade always represents the percentage of available phosphate (P₂O₅), which is 20%.
Question 3: Which form of phosphorus do plant roots actually absorb from the soil solution?
- Polyphosphate (P₃O₁₀)
- Orthophosphate (H₂PO₄⁻ or HPO₄²⁻) (Correct answer)
- Apatite mineral form
- Organic phytate form
Correct answer: Orthophosphate (H₂PO₄⁻ or HPO₄²⁻)
Plant roots absorb phosphorus as orthophosphate ions (H₂PO₄⁻ or HPO₄²⁻) from the soil solution.
Question 4: Sulfur-coated urea releases nitrogen more slowly than regular urea primarily because:
- Sulfur increases soil pH, slowing nitrification
- The coating must degrade before water can dissolve the urea (Correct answer)
- Urea inside the coating has lower nitrogen content
- Sulfur reacts with urea to form a stable compound
Correct answer: The coating must degrade before water can dissolve the urea
The sulfur coating acts as a physical barrier; moisture must penetrate or degrade it before the urea core dissolves and becomes available.
Question 5: When manure is surface-applied without incorporation, the greatest nutrient loss risk is:
- Potassium leaching
- Phosphorus volatilization
- Ammonia volatilization from nitrogen (Correct answer)
- Sulfur oxidation
Correct answer: Ammonia volatilization from nitrogen
Ammonium-nitrogen in unincorporated manure readily volatilizes as ammonia gas, especially in warm, windy conditions.
Question 6: Which potassium fertilizer also supplies sulfur, making it useful on sulfur-deficient soils?
- Muriate of potash (KCl)
- Potassium nitrate (KNO₃)
- Sulfate of potash (K₂SO₄) (Correct answer)
- Potassium carbonate (K₂CO₃)
Correct answer: Sulfate of potash (K₂SO₄)
Sulfate of potash (K₂SO₄) provides both potassium and sulfur, benefiting crops on sulfur-deficient soils.
Question 7: A soil test recommends 60 lb P₂O₅/acre. If triple superphosphate (0-46-0) is used, approximately how many pounds per acre are needed?
- 28 lb/acre
- 60 lb/acre
- 130 lb/acre (Correct answer)
- 276 lb/acre
Correct answer: 130 lb/acre
Dividing the recommendation by the decimal fraction of P₂O₅: 60 ÷ 0.46 ≈ 130 lb/acre of triple superphosphate.
CFA Nutrient Sources and Management 2
Which fertilizer material is considered an organic nitrogen source because it releases nitrogen through microbial decomposition?