What is ET-based irrigation scheduling?

• A. Scheduling irrigation based on evapotranspiration to match plant water demand efficiently.
• B. Scheduling irrigation only on weekends.
• C. Scheduling irrigation based on soil type alone.
• D. Scheduling irrigation to maximize lawn greenness regardless of water demand.

Answer: (A)

ET-based irrigation scheduling uses evapotranspiration to guide when and how much water to apply, so the irrigation matches the crop’s actual water demand. Evapotranspiration represents the combined loss of water from soil evaporation and plant transpiration, and it responds to weather conditions like temperature, humidity, wind, and sunlight, as well as crop type and growth stage. By estimating reference evapotranspiration (ETo) from weather data and multiplying by a crop coefficient (Kc) for the specific crop and growth stage, you get crop evapotranspiration (ETc), which estimates how much water the plant needs in a given period. The irrigation plan then aims to replace ETc in a controlled way, considering soil water-holding capacity and how much water can be stored in the root zone (allowable depletion). This approach maximizes water-use efficiency because it aligns watering with actual plant demand, helps prevent moisture stress, and avoids wasting water.

Scheduling irrigation just on weekends ignores dynamic plant needs and weather-driven water loss. Relying on soil type alone misses how quickly soil dries under real conditions and how much water the crop is using. Trying to maximize lawn greenness without regard to water demand can lead to overwatering or waste when conditions require less water.