CH Plant Nutrition and Fertilization 1 — Questions and Answers
Question 1: Which macronutrient is most often responsible for the yellowing of older leaves (chlorosis) in nitrogen-deficient plants?
- Nitrogen (Correct answer)
- Phosphorus
- Potassium
- Calcium
Correct answer: Nitrogen
Nitrogen is a mobile nutrient that moves from older leaves to younger growth, causing older leaves to yellow first when deficient.
Question 2: A fertilizer labeled 10-10-10 contains equal percentages of which three primary nutrients?
- Nitrogen, Phosphorus, Potassium (Correct answer)
- Nitrogen, Calcium, Magnesium
- Phosphorus, Sulfur, Iron
- Potassium, Boron, Manganese
Correct answer: Nitrogen, Phosphorus, Potassium
The three numbers on a fertilizer label (N-P-K) represent the percentage by weight of nitrogen, phosphorus (as P2O5), and potassium (as K2O).
Question 3: Which soil pH range generally maximizes nutrient availability for most landscape plants?
- 4.0–5.0
- 5.5–6.5 (Correct answer)
- 7.5–8.5
- 8.5–9.5
Correct answer: 5.5–6.5
A pH of 5.5–6.5 keeps most macro- and micronutrients in plant-available forms and is the optimum range for the majority of landscape species.
Question 4: Iron deficiency interveinal chlorosis on young leaves is most commonly caused by which soil condition?
- Low soil pH
- High soil pH (Correct answer)
- Excessive nitrogen
- Low soil temperature
Correct answer: High soil pH
High soil pH (alkaline conditions) causes iron to precipitate into unavailable forms, resulting in interveinal chlorosis on new leaves.
Question 5: Slow-release fertilizers benefit landscape plants primarily because they:
- Increase salt index immediately
- Reduce leaching and provide sustained nutrition (Correct answer)
- Lower soil pH rapidly
- Eliminate the need for micronutrients
Correct answer: Reduce leaching and provide sustained nutrition
Slow-release fertilizers break down gradually, reducing nutrient leaching and providing a steady supply of nutrients over weeks or months.
Question 6: Magnesium is considered a secondary macronutrient and is an essential component of which plant molecule?
- Cellulose
- Chlorophyll (Correct answer)
- Lignin
- Pectin
Correct answer: Chlorophyll
Magnesium is the central atom in the chlorophyll molecule, making it critical for photosynthesis and green coloration.
CH Plant Nutrition and Fertilization 1
Which macronutrient is most often responsible for the yellowing of older leaves (chlorosis) in nitrogen-deficient plants?