Formulas
- Crop water use (ETc) = ET₀ × Kc, in mm per day
- Liters per day = (ETc − effective rain) × area in m² ÷ efficiency
- Run time = liters ÷ flow of the system
1 mm of water over 1 m² is exactly 1 liter.
Example
With ET₀ of 5 mm/day, Kc 1.0, 1,000 m² and drip irrigation (90% efficient), you need about 5,556 liters per day. With 1,000 L/h of flow, that is 5 h 33 min of irrigation.
Efficiency of each system
- Drip: about 90%.
- Center pivot: about 85%.
- Sprinklers: about 75%.
- Surface or furrow: about 60%.
Frequently asked questions
Where do I find ET₀?
Weather services and agricultural extension sites publish daily reference evapotranspiration. Hot, dry and windy days have higher values.
What Kc should I use?
It depends on the crop and its stage. Most crops start near 0.4, reach 1.0 to 1.2 at full growth and fall again near harvest.
See also
Results are estimates for information only and are not financial, legal or medical advice. Rates, taxes and fees vary — confirm with a professional or your lender.