CIT Soil Science and Plant Water Requirements 2 — Questions and Answers
Question 1: The effective root depth of cool-season turfgrass used for irrigation scheduling is typically:
- 1 to 2 inches
- 4 to 6 inches (Correct answer)
- 12 to 18 inches
- 24 to 36 inches
Correct answer: 4 to 6 inches
Cool-season turfgrasses such as Kentucky bluegrass and tall fescue have active root zones of approximately 4 to 6 inches under typical managed conditions.
Question 2: If the reference ET is 0.25 inches/day and the crop coefficient (Kc) is 0.8, the crop water requirement is:
- 0.25 inches/day
- 0.20 inches/day (Correct answer)
- 0.31 inches/day
- 0.80 inches/day
Correct answer: 0.20 inches/day
Crop ET equals reference ET multiplied by the crop coefficient: 0.25 × 0.8 = 0.20 inches per day.
Question 3: A Management Allowable Depletion (MAD) of 50% means irrigation should be triggered when:
- 50% of total soil volume has dried out
- 50% of plant available water has been consumed (Correct answer)
- Soil moisture drops below 50% of saturation level
- Plants show 50% visible drought stress symptoms
Correct answer: 50% of plant available water has been consumed
MAD of 50% means you irrigate when half of the plant available water — the range between field capacity and wilting point — has been depleted.
Question 4: Which soil moisture sensor type measures moisture by analyzing electromagnetic wave propagation through the soil?
- Tensiometer
- TDR/FDR sensor (Correct answer)
- Granular matrix sensor
- Neutron probe
Correct answer: TDR/FDR sensor
Time Domain Reflectometry (TDR) and Frequency Domain Reflectometry (FDR) sensors determine volumetric water content by measuring how electromagnetic signals travel through soil.
Question 5: On the USDA soil texture triangle, a soil with 40% sand, 40% silt, and 20% clay is classified as:
- Sandy clay loam
- Loam (Correct answer)
- Silt loam
- Clay loam
Correct answer: Loam
A roughly balanced distribution of sand, silt, and moderate clay places this soil squarely in the loam category on the USDA texture triangle.
Question 6: In a managed turfgrass landscape, which factor most directly determines required irrigation frequency?
- The age and manufacturer of the irrigation system
- The type of sprinkler heads installed
- The rate of ET relative to soil water storage capacity in the root zone (Correct answer)
- The color and variety of grass species
Correct answer: The rate of ET relative to soil water storage capacity in the root zone
Irrigation frequency is primarily determined by how quickly ET depletes the soil water reservoir within the root zone down to the MAD threshold.
Question 7: Pushing a screwdriver or soil probe into the ground is a simple field method to quickly estimate:
- Soil pH and nutrient level
- Soil compaction and moisture level (Correct answer)
- Nitrogen and phosphorus content
- Organic matter percentage
Correct answer: Soil compaction and moisture level
Easy probe penetration indicates moist, non-compacted soil, while significant resistance indicates dryness or compaction, providing a quick field diagnostic.
CIT Soil Science and Plant Water Requirements 2
The effective root depth of cool-season turfgrass used for irrigation scheduling is typically: