CIT Soil Science and Plant Water Requirements 1 — Questions and Answers
Question 1: Which soil type has the highest water-holding capacity?
- Sandy soil
- Clay soil (Correct answer)
- Loamy sand
- Gravelly soil
Correct answer: Clay soil
Clay soil has the smallest particle size and greatest surface area, allowing it to retain more water than coarser-textured soils.
Question 2: Field capacity is defined as the soil moisture level that remains after:
- Plants have absorbed all usable water
- Excess water has drained away by gravity (Correct answer)
- The soil is fully saturated by heavy rain
- The permanent wilting point is reached
Correct answer: Excess water has drained away by gravity
Field capacity is the water content remaining in soil 24–48 hours after saturation, once gravitational drainage has stopped.
Question 3: The permanent wilting point is the soil moisture level at which:
- Sandy soils can no longer hold water
- Irrigation must begin immediately to prevent stress
- Plants can no longer extract water and wilt permanently (Correct answer)
- Field capacity is re-established
Correct answer: Plants can no longer extract water and wilt permanently
At the permanent wilting point, remaining soil water is held too tightly by soil particles for plant roots to extract it, causing irreversible wilting.
Question 4: Which of the following best describes evapotranspiration (ET)?
- The rate at which water drains below the root zone
- The combined loss of water through soil evaporation and plant transpiration (Correct answer)
- The total rainfall received by a landscape in a season
- The efficiency rating of an irrigation system
Correct answer: The combined loss of water through soil evaporation and plant transpiration
ET represents total landscape water demand by combining direct evaporation from soil and transpiration through plant leaves.
Question 5: Plant Available Water (PAW) is correctly calculated as:
- Field capacity minus permanent wilting point (Correct answer)
- Saturation minus field capacity
- Total precipitation minus surface runoff
- Irrigation depth minus evaporation losses
Correct answer: Field capacity minus permanent wilting point
PAW is the range of soil moisture between field capacity and permanent wilting point that plant roots can actually extract and use.
Question 6: Sandy soils typically have infiltration rates closest to which range?
- 0.1 to 0.2 inches per hour
- 0.3 to 0.5 inches per hour
- 0.5 to 1.0 inches per hour
- 1.5 to 3.0 inches per hour (Correct answer)
Correct answer: 1.5 to 3.0 inches per hour
Sandy soils have large pore spaces that allow rapid water infiltration, typically at rates of 1.5 to 3.0 inches per hour.
Question 7: Which soil texture is most recommended for turfgrass because it balances drainage and moisture retention?
- Sandy loam (Correct answer)
- Pure clay
- Pure sand
- Gravel
Correct answer: Sandy loam
Sandy loam provides adequate drainage to prevent waterlogging while retaining enough moisture and nutrients to support healthy turfgrass growth.
CIT Soil Science and Plant Water Requirements 1
Which soil type has the highest water-holding capacity?