CCA Irrigation Management and Water Use 1 — Questions and Answers
Question 1: Which irrigation method typically achieves the highest application efficiency for row crops by delivering water directly to the root zone?
- Surface furrow irrigation
- Center-pivot sprinkler irrigation
- Drip/trickle irrigation (Correct answer)
- Flood irrigation
Correct answer: Drip/trickle irrigation
Drip/trickle irrigation delivers water directly to the root zone with minimal evaporation or runoff losses, typically achieving 90–95% application efficiency.
Question 2: Evapotranspiration (ET) as used in irrigation scheduling represents:
- Only the water lost through plant leaf transpiration
- The combined water loss from soil evaporation and plant transpiration (Correct answer)
- The amount of rainfall minus runoff
- The rate at which water infiltrates the soil profile
Correct answer: The combined water loss from soil evaporation and plant transpiration
ET combines water evaporated from the soil surface and water transpired by plants, and is the primary measure used to estimate crop water demand for scheduling irrigations.
Question 3: The crop coefficient (Kc) used in reference ET-based irrigation scheduling primarily accounts for:
- Soil water-holding capacity differences across fields
- Differences in water use between a reference crop and the actual crop at various growth stages (Correct answer)
- The efficiency of the irrigation delivery system
- Precipitation probability during the growing season
Correct answer: Differences in water use between a reference crop and the actual crop at various growth stages
Kc adjusts reference ET (ETo) for a specific crop and growth stage, reflecting differences in canopy cover, root depth, and plant physiology compared to the reference (typically grass or alfalfa).
Question 4: Soil texture most directly affects irrigation scheduling because it determines:
- The crop's genetic water use efficiency
- Soil water-holding capacity and infiltration rate (Correct answer)
- The oxygen demand of soil microorganisms
- The evaporative demand of the atmosphere
Correct answer: Soil water-holding capacity and infiltration rate
Soil texture controls pore size distribution, which dictates how much plant-available water a soil can hold (field capacity minus wilting point) and how rapidly water moves through the profile.
Question 5: Which soil water content term represents the upper limit of plant-available water after drainage has ceased?
- Permanent wilting point
- Saturation
- Field capacity (Correct answer)
- Plant-available water capacity
Correct answer: Field capacity
Field capacity is the water content remaining after gravitational drainage has essentially stopped (typically 1–3 days after wetting) and represents the upper limit of readily plant-available water.
Question 6: A producer wants to irrigate when soil water depletion reaches 50% of available water capacity. This practice is called:
- Regulated deficit irrigation
- Management allowable depletion (MAD) scheduling (Correct answer)
- Pulse irrigation
- Gravitational depletion management
Correct answer: Management allowable depletion (MAD) scheduling
Management Allowable Depletion (MAD) defines the fraction of plant-available water that can be depleted before the next irrigation is triggered, with 50% being a common threshold for most field crops.
Question 7: Which instrument is commonly used in the field to measure soil water matric potential and assist in irrigation scheduling?
- Tensiometer (Correct answer)
- Psychrometer
- Gypsum block conductivity sensor only when used above field capacity
- Rain gauge
Correct answer: Tensiometer
Tensiometers measure the matric potential (tension) with which water is held in the soil, providing a direct indicator of how hard plant roots must work to extract water and when irrigation is needed.
CCA Irrigation Management and Water Use 1
Which irrigation method typically achieves the highest application efficiency for row crops by delivering water directly to the root zone?