CFA Interpreting Fertilizer Labels 2 — Questions and Answers
Question 1: A fertilizer label reads 'guaranteed analysis: total nitrogen 10%.' What does 'guaranteed analysis' mean?
- The minimum nutrient content the manufacturer promises to deliver (Correct answer)
- The exact nutrient content measured in every bag
- The maximum nutrient content allowed by law
- An estimate based on raw material averages
Correct answer: The minimum nutrient content the manufacturer promises to deliver
Guaranteed analysis is the minimum nutrient content the manufacturer is legally required to deliver, not an exact or average measurement.
Question 2: On a fertilizer label, 'available phosphate (P2O5)' refers to which form of phosphorus?
- Total phosphorus in the product regardless of solubility
- Phosphorus expressed as elemental P in pounds
- Water-soluble plus citrate-soluble phosphate fractions (Correct answer)
- Only the phosphorus that dissolves in water
Correct answer: Water-soluble plus citrate-soluble phosphate fractions
Available P2O5 includes both the water-soluble fraction and the citrate-soluble fraction, as both are considered plant-available.
Question 3: A bag states 'derived from: urea, ammonium sulfate.' What does this tell the applicator?
- The nitrogen percentage split between forms
- The source materials from which nutrients were made (Correct answer)
- The order of application recommended
- The soil types for which the product is approved
Correct answer: The source materials from which nutrients were made
The 'derived from' statement identifies the raw ingredient sources, helping applicators understand nutrient forms and potential soil interactions.
Question 4: Which label section specifies how much product to apply per 1,000 square feet for a lawn?
- Guaranteed analysis
- Application directions (Correct answer)
- Precautionary statements
- Net weight statement
Correct answer: Application directions
Application directions (sometimes called directions for use) provide rate recommendations by area for various crop or turf situations.
Question 5: A label shows 'sulfur (S) 12%.' In which of the following contexts is this information most critical?
- When calculating the cost per pound of nitrogen
- When determining whether irrigation is required
- When applying to soils already high in sulfur or to acid-sensitive crops (Correct answer)
- When checking for phosphorus interaction with iron
Correct answer: When applying to soils already high in sulfur or to acid-sensitive crops
High sulfur content is most critical on soils already elevated in sulfur or when growing acid-sensitive crops, since sulfur oxidizes to sulfuric acid.
Question 6: What does the term 'slowly available nitrogen' on a fertilizer label indicate?
- Nitrogen that requires tillage to become available
- Nitrogen released over time through microbial or chemical breakdown (Correct answer)
- Nitrogen that is only available in alkaline soils
- Nitrogen that has been stabilized with a urease inhibitor only
Correct answer: Nitrogen released over time through microbial or chemical breakdown
Slowly available (or slow-release) nitrogen is released gradually through microbial decomposition or chemical hydrolysis, reducing leaching and burn risk.
Question 7: A fertilizer label lists 'chlorine (Cl) not more than 3%.' Why is a maximum, rather than a minimum, stated for chlorine?
- Chlorine is a secondary macronutrient that must be maximized
- High chlorine can be toxic to chloride-sensitive crops, so a cap protects the grower (Correct answer)
- Chlorine is regulated by EPA as a hazardous substance above 3%
- Labels are only required to state maximums for micronutrients
Correct answer: High chlorine can be toxic to chloride-sensitive crops, so a cap protects the grower
Chloride-sensitive crops like strawberries and some vegetables can be damaged by excessive chlorine, so the label caps it to assure growers the product is safe for those crops.
CFA Interpreting Fertilizer Labels 2
A fertilizer label reads 'guaranteed analysis: total nitrogen 10%.' What does 'guaranteed analysis' mean?