What is evapotranspiration (ET) and how is it used to create an irrigation schedule for a turf area?

• A. ET is the combination of evaporation from soil and transpiration from plants; irrigation is planned to replace ET (plus rainfall) while considering soil water-holding capacity and drainage
• B. ET stands for estimated turf
• C. ET is only rainfall
• D. ET is used to measure soil color and texture

Answer: (A)

Evapotranspiration is the total water lost from a turf area through evaporation from the soil surface and transpiration by the grass plants. This value shows how much water the turf needs to replace to keep the soil moist without stressing the roots. To create an irrigation schedule, you estimate how much water must be replenished over a period (often daily or weekly) by using ET figures and incorporating any effective rainfall. The goal is to bring soil moisture back to a desirable level—often near field capacity—while accounting for the soil’s holding capacity and its drainage characteristics to avoid overwatering or runoff. In practice, you subtract the amount of rainfall that actually contributes to soil moisture (effective rainfall) from the ET requirement and apply the remaining water through irrigation, adjusted for the specific turf and soil conditions.