Irrigation Water Requirement
Crop water need (ETc), net and gross irrigation depth and total water volume for a field.
Inputs
mm/day
mm/day
%
ha
days
Results
- Water required
- 4,200 m³
- Crop water need (ETc)
- 5.5 mm/day
- Net irrigation
- 4.5 mm/day
- Gross irrigation
- 6 mm/day
Formula
ETc = ET₀ × Kc
Net = ETc − effective rainfall
Gross = Net ÷ efficiency
Volume (m³) = Gross mm × area ha × 10 × days
Assumptions & limits
- FAO-56 single crop coefficient method.
- Efficiency: surface 50–70%, sprinkler 70–80%, drip 85–95%.
- 1 mm over 1 ha = 10 m³.
Worked example
5 × 1.1 = 5.5 − 1 = 4.5 mm ÷ 0.75 = 6 mm/day × 10 ha × 10 × 7 = 4,200 m³.