ISA Soil Management 3 — Questions and Answers
Question 1: A soil test reports a pH of 5.0. Which amendment would most effectively raise the pH?
- Sulfur
- Iron sulfate
- Ground limestone (calcitic lime) (Correct answer)
- Peat moss
Correct answer: Ground limestone (calcitic lime)
Calcitic lime (calcium carbonate) neutralizes soil acidity and raises pH, making nutrients more available.
Question 2: Which soil horizon is typically richest in organic matter and most important for tree root activity?
- O horizon
- A horizon (Correct answer)
- B horizon
- C horizon
Correct answer: A horizon
The A horizon (topsoil) contains the highest concentration of organic matter and supports the most active root zone.
Question 3: Nitrogen deficiency in trees typically presents as:
- Purple or reddish coloration of leaves
- Uniform yellowing of older leaves first (Correct answer)
- Interveinal chlorosis on young leaves
- Marginal leaf scorch
Correct answer: Uniform yellowing of older leaves first
Nitrogen is mobile in the plant, so deficiency symptoms appear first on older leaves as nitrogen is redirected to new growth.
Question 4: What is the recommended depth for applying organic mulch around trees?
- 1 inch
- 2–4 inches (Correct answer)
- 6–8 inches
- 10–12 inches
Correct answer: 2–4 inches
A 2–4 inch mulch layer conserves moisture and moderates temperature without creating anaerobic conditions at the root flare.
Question 5: Which soil type is most prone to waterlogging and anaerobic conditions?
- Sandy soil
- Loamy sand
- Gravelly soil
- Clay soil (Correct answer)
Correct answer: Clay soil
Clay soil's fine particles create micropores that drain very slowly, leading to persistent waterlogged, oxygen-poor conditions.
Question 6: Mycorrhizal fungi benefit trees primarily by:
- Fixing atmospheric nitrogen
- Extending the effective root surface area for water and nutrient uptake (Correct answer)
- Decomposing organic matter into humus
- Producing growth hormones that stimulate trunk elongation
Correct answer: Extending the effective root surface area for water and nutrient uptake
Mycorrhizal hyphae extend far beyond root tips, dramatically increasing the volume of soil a tree can access for water and phosphorus.
Question 7: Soil salinity damages trees primarily by:
- Raising soil pH above 8.0
- Creating osmotic stress that limits water uptake (Correct answer)
- Blocking iron and manganese absorption
- Compacting soil particles together
Correct answer: Creating osmotic stress that limits water uptake
High salt concentrations lower the osmotic potential of soil water, making it harder for roots to absorb water even when the soil appears moist.
ISA Soil Management 3
A soil test reports a pH of 5.0.
Which amendment would most effectively raise the pH?