Variables
Description
What is this formula?
The Crop Evapotranspiration equation calculates the actual water demand of a crop by multiplying the reference evapotranspiration by a crop coefficient.
When to use it
Use this equation when determining irrigation requirements, estimating crop water consumption, and scheduling irrigation applications.
Example
Given:
ET0 = 5.8 mm/day
Kc = 1.15
Formula:
ETc = Kc × ET0
Substitution:
ETc = 1.15 × 5.8
ETc = 6.67 mm/day
Result:
The crop evapotranspiration is 6.67 mm/day.
Applications
- Irrigation scheduling
- Crop water requirement estimation
- Agricultural water management
- Irrigation system design
- Water allocation planning
Note
This equation is part of the FAO crop coefficient approach and is considered the standard method for estimating crop water requirements.
The accuracy of the result depends primarily on the quality of ET0 and the selected crop coefficient Kc.
Crop coefficients vary according to crop type, growth stage, climate, irrigation method, and local management practices.
For many crops, different Kc values are used during the initial, development, mid-season, and late-season growth stages.
Using an inappropriate Kc value can introduce larger errors than the ET0 estimation itself.