What inputs does a weather-based ET controller use to adjust irrigation schedules?

• A. Soil type only.
• B. ET data and weather inputs.
• C. Water metering data only.
• D. Fixed time of day only.

Answer: (B)

Weather-based ET controllers adjust irrigation by estimating how much water plants lose to the atmosphere and scheduling irrigation accordingly. They rely on evapotranspiration data (ET) together with current weather measurements—temperature, humidity, wind speed, and solar radiation—with rainfall often factored in. This lets the controller calculate daily plant water needs and apply the appropriate amount, rather than irrigating on a fixed schedule. Relying only on soil type misses how weather changes ET; relying only on water metering data doesn’t anticipate future water losses; and using a fixed time of day ignores weather-driven swings in ET.