CFB Soil Science & Amendments 2 — Questions and Answers
Question 1: Which soil texture has the highest water-holding capacity per unit volume?
- Coarse sand
- Sandy loam
- Clay (Correct answer)
- Fine gravel
Correct answer: Clay
Clay has the smallest particles, the greatest surface area, and the smallest pore spaces, allowing it to retain the most water per unit volume.
Question 2: On a soil penetrometer, readings consistently above 300 psi typically indicate:
- Optimal root zone conditions for turfgrass
- Severe compaction that significantly restricts root growth (Correct answer)
- Ideal moisture levels for game day use
- Adequate macropore space in the root zone
Correct answer: Severe compaction that significantly restricts root growth
Penetrometer readings above 300 psi signal severe compaction that physically prevents root penetration and reduces turfgrass vigor.
Question 3: Calcitic limestone is applied to sports field soils primarily to:
- Improve macropore drainage
- Raise soil pH by neutralizing acidity (Correct answer)
- Add organic matter to the root zone
- Reduce surface compaction after heavy use
Correct answer: Raise soil pH by neutralizing acidity
Calcitic limestone (calcium carbonate) reacts with hydrogen ions in acidic soils to raise pH toward the optimal range for turfgrass.
Question 4: According to USGA green construction specifications, approximately what percentage of the root zone mix is sand?
- 30–40%
- 50–60%
- 60–70%
- 80–100% (Correct answer)
Correct answer: 80–100%
USGA-specification root zones are predominantly sand (80–100%) with a small peat fraction to achieve the required infiltration rates of at least 6 inches per hour.
Question 5: Which amendment improves both drainage AND cation exchange capacity in sports field soils?
- Coarse sand
- Calcite powder
- Calcined clay (e.g., Turface) (Correct answer)
- Elemental sulfur
Correct answer: Calcined clay (e.g., Turface)
Calcined clay products like Turface have a highly porous structure that improves drainage and also possess elevated CEC for nutrient retention.
Question 6: What is the primary concern with incorporating excessive organic matter into a sports field root zone?
- It raises pH too rapidly, causing nutrient lockout
- It decomposes over time, leading to settling and reduced drainage (Correct answer)
- It immediately repels water causing hydrophobic conditions
- It permanently increases compaction resistance
Correct answer: It decomposes over time, leading to settling and reduced drainage
As organic matter decomposes, pore space decreases, the mix settles, and drainage capacity declines — often within a few years of construction.
Question 7: What does soil bulk density measure?
- The weight of solid soil particles only, excluding pore space
- The mass of dry soil per unit of total volume, including pore spaces (Correct answer)
- The total water content of a saturated soil sample
- The compressive load the soil can bear before failure
Correct answer: The mass of dry soil per unit of total volume, including pore spaces
Bulk density is mass of oven-dry soil divided by total soil volume (solids + pores), and is a key indicator of compaction and porosity.
CFB Soil Science & Amendments 2
Which soil texture has the highest water-holding capacity per unit volume?