CFA Interpreting Fertilizer Labels Questions and Answers 1 — Questions and Answers
Question 1: An applicator needs to apply 1.5 lbs of actual nitrogen (N) per 1,000 sq ft. They are using a fertilizer with a guaranteed analysis of 25-5-10. How many pounds of this fertilizer product must be applied per 1,000 sq ft?
- 4.5 lbs
- 5.0 lbs
- 6.0 lbs (Correct answer)
- 7.5 lbs
Correct answer: 6.0 lbs
The first number in the N-P-K analysis represents the percentage of nitrogen by weight. To find how much fertilizer product is needed to deliver a specific amount of actual nitrogen, divide the desired amount of nitrogen by the percentage of nitrogen in the bag (in decimal form). Calculation: 1.5 lbs N / 0.25 = 6.0 lbs of fertilizer product.
Question 2: A fertilizer label for a 50 lb bag of 10-20-20 also lists 'Potential Acidity: 400 lbs Calcium Carbonate Equivalent per ton'. What does this statement signify?
- The fertilizer will lower the soil pH over time, and its acidifying effect is equivalent to that produced by 400 lbs of limestone per ton of fertilizer applied. (Correct answer)
- Applying one ton of this fertilizer has the same effect as adding 400 lbs of calcium carbonate, raising the soil pH.
- The product contains 400 pounds of calcium carbonate per ton to buffer the soil against pH changes.
- For every ton of fertilizer applied, 400 lbs of acidic compounds are released into the soil.
Correct answer: The fertilizer will lower the soil pH over time, and its acidifying effect is equivalent to that produced by 400 lbs of limestone per ton of fertilizer applied.
The 'Potential Acidity' on a fertilizer label indicates the product's tendency to lower soil pH over time. The value, expressed in Calcium Carbonate (limestone) Equivalent, represents the amount of limestone needed to neutralize the acidity caused by applying one ton of the fertilizer.
Question 3: A turf manager is applying fertilizer near newly germinated seeds and wants to minimize the risk of 'fertilizer burn'. Which of the following characteristics listed on a fertilizer label is the most direct indicator of this risk?
- Percentage of water-insoluble nitrogen
- Guaranteed analysis (N-P-K ratio)
- Salt Index (Correct answer)
- Micronutrient content
Correct answer: Salt Index
The Salt Index is a measure of the salt concentration a fertilizer induces in the soil solution. Fertilizers with a high salt index have a greater potential to cause 'fertilizer burn' or desiccation injury to seeds and young plants by creating an osmotic imbalance that draws water out of plant tissues.
Question 4: A fertilizer label displays a guaranteed analysis of 12-8-10. It also specifies that 3% of the total nitrogen is from ammoniacal nitrogen and 9% is from nitrate nitrogen. Which of the following statements is most accurate regarding this nitrogen composition?
- All the nitrogen is in a slow-release form.
- The majority of the nitrogen is immediately available for plant uptake but is also more susceptible to leaching. (Correct answer)
- The fertilizer has a strong acidifying effect due to the high ammoniacal nitrogen content.
- The nitrogen will become available gradually over a period of 3 to 9 months.
Correct answer: The majority of the nitrogen is immediately available for plant uptake but is also more susceptible to leaching.
Nitrate nitrogen is a form that is immediately available for plants to absorb. However, because it is highly water-soluble and does not bind to soil particles, it is also the form most prone to leaching below the root zone. Since 9% of the 12% total N is nitrate, this is the dominant form.
Question 5: The guaranteed analysis on a fertilizer bag reads 15-0-30 and also guarantees 2% Magnesium (Mg) and 5% Sulfur (S). How many pounds of actual potash (K2O) and sulfur (S) are in a 50 lb bag of this product?
- 30 lbs of K2O and 5 lbs of S
- 15 lbs of K2O and 2.5 lbs of S (Correct answer)
- 7.5 lbs of K2O and 1 lb of S
- 30 lbs of K2O and 2.5 lbs of S
Correct answer: 15 lbs of K2O and 2.5 lbs of S
The guaranteed analysis numbers are percentages by weight. To find the pounds of a nutrient in a bag, multiply the bag's weight by the nutrient's percentage (in decimal form). Potash (K2O) is the third number (30%), and Sulfur (S) is listed at 5%. Calculation: Potash = 50 lbs * 0.30 = 15 lbs. Sulfur = 50 lbs * 0.05 = 2.5 lbs.
Question 6: The second number in the N-P-K guaranteed analysis on a fertilizer label legally represents the percentage by weight of which compound?
- Elemental Phosphorus (P)
- Available Phosphate (P2O5) (Correct answer)
- Phosphoric Acid (H3PO4)
- Water-Soluble Phosphorus (P)
Correct answer: Available Phosphate (P2O5)
By law and industry standard, the three numbers in the N-P-K analysis represent Total Nitrogen (N), Available Phosphate (P2O5), and Soluble Potash (K2O), respectively. Therefore, the second number indicates the percentage of P2O5, not elemental phosphorus.
CFA Interpreting Fertilizer Labels Questions and Answers 1
An applicator needs to apply 1.5 lbs of actual nitrogen (N) per 1,000 sq ft.
They are using a fertilizer with a guaranteed analysis of 25-5-10.
How many pounds of this fertilizer product must be applied per 1,000 sq ft?