IA Irrigation Scheduling & Evapotranspiration 2 — Questions and Answers
Question 1: Which weather variable has the greatest influence on reference evapotranspiration (ETo) in humid climates?
- Wind speed
- Net radiation (Correct answer)
- Relative humidity
- Soil temperature
Correct answer: Net radiation
Net radiation is typically the dominant driver of ETo in humid climates where vapor pressure deficit is lower.
Question 2: The 'checkbook method' of irrigation scheduling tracks what two primary inputs?
- Fertilizer and pH
- Rainfall and ET (Correct answer)
- Temperature and wind
- Runoff and deep percolation
Correct answer: Rainfall and ET
The checkbook method balances rainfall and ET as deposits and withdrawals to maintain soil moisture within an acceptable range.
Question 3: What does the term 'irrigation interval' refer to?
- The duration of each watering event
- The number of sprinkler heads per zone
- The number of days between irrigation events (Correct answer)
- The pressure loss across a valve
Correct answer: The number of days between irrigation events
Irrigation interval is the number of days between scheduled watering events, determined by depletion rate and MAD.
Question 4: If daily ETo is 0.25 inches and the crop coefficient is 0.8, what is the daily crop water use (ETc)?
- 0.05 inches
- 0.20 inches (Correct answer)
- 0.31 inches
- 0.45 inches
Correct answer: 0.20 inches
ETc = ETo × Kc = 0.25 × 0.8 = 0.20 inches per day.
Question 5: Which instrument is used to directly measure reference evapotranspiration in the field?
- Anemometer
- Lysimeter (Correct answer)
- Piezometer
- Tensiometer
Correct answer: Lysimeter
A lysimeter is a precision device that measures actual water use by plants by weighing or monitoring drainage from an isolated soil-plant system.
Question 6: Which factor does NOT directly influence evapotranspiration rates?
- Solar radiation
- Wind speed
- Soil pH (Correct answer)
- Relative humidity
Correct answer: Soil pH
Soil pH affects nutrient availability and plant health but is not a direct meteorological driver of evapotranspiration.
IA Irrigation Scheduling & Evapotranspiration 2
Which weather variable has the greatest influence on reference evapotranspiration (ETo) in humid climates?