What is evapotranspiration (ET) irrigation scheduling?

• A. Scheduling based on plant water use data to determine when and how much to irrigate.
• B. Scheduling based on precipitation only.
• C. Scheduling based on soil color.
• D. Scheduling based on system age.

Answer: (B)

ET irrigation scheduling revolves around estimating how much water the crop actually loses to evaporation and transpiration, then using that information to decide when to water and how much to apply. In practice, this means calculating crop water use by combining weather data (like temperature, humidity, wind, solar radiation) with a crop coefficient that reflects how a specific plant uses water at its growth stage. The result, ETc, tells you the real water demand of the crop, so irrigation can be timed and sized to replace that exact amount and keep the root zone within an optimal moisture range.

This approach contrasts with watering based on precipitation alone, which misses the ongoing water losses that occur after rainfall and can lead to under- or over-watering. Soil color and system age don’t directly indicate how much water the crop needs, so they aren’t used to schedule irrigation in the ET framework.

So, the best description is scheduling based on plant water use data to determine when and how much to irrigate, because it relies on the crop’s actual water demand rather than relying solely on rainfall or other unrelated factors.