How is crop water requirement calculated?

Crop water requirement = ET₀ × Kc, where ET₀ is the reference evapotranspiration (mm/day) for your climate and Kc is the FAO-56 crop coefficient. The result is the daily water depth the crop needs. Multiply by field area (in m²) to get total litres (1 mm over 1 m² = 1 litre).

What is ET₀ in irrigation?

ET₀ (reference evapotranspiration) is the amount of water evaporated from a standardised short grass surface under your local climate conditions, expressed in mm/day. It accounts for temperature, humidity, wind, and solar radiation. Arid regions typically see 7–9 mm/day while temperate climates see 2–4 mm/day.

What is a crop coefficient (Kc)?

The crop coefficient (Kc) adjusts ET₀ for the specific crop type and growth stage. Values come from FAO Irrigation and Drainage Paper 56. Grass has Kc ≈1.0, maize mid-season Kc ≈1.2, and tomatoes mid-season Kc ≈1.15.

Why does applied water exceed needed water?

No irrigation system is 100% efficient. Drip irrigation loses ≈8% to dripper variation and soil wetting losses. Sprinklers lose ≈20% to wind drift and evaporation. Surface flooding loses 40% or more to runoff and deep percolation. The calculator automatically inflates the applied volume to account for these losses.

How do I calculate irrigation run time?

Run time (hours) = Total volume to apply (litres) ÷ System flow rate (litres/hour). Enter your pump or system flow rate in the calculator and it computes the run time automatically.

Irrigation Calculator

Calculate daily crop water requirements, total volume to apply, and runtime for your irrigation system. Based on FAO-56 standards.

IrrigationCalculator.climateEt0

IrrigationCalculator.climateZone

IrrigationCalculator.crop

IrrigationCalculator.fieldArea

≈ 10,000 m²

IrrigationCalculator.measureOnMap

IrrigationCalculator.irrigationSystem

IrrigationCalculator.systemType

IrrigationCalculator.flowRate

L/hr

Results

IrrigationCalculator.waterNeeded

4.5 mm/day

ET₀ 4.5 × Kc 1

IrrigationCalculator.waterNeeded

crop demand

45,000 L

IrrigationCalculator.waterToApply

at 92% efficiency

48,913 L

IrrigationCalculator.runTime

97.8 h

IrrigationCalculator.flowRate

500 L/hr

92% system efficiency — 8% lost to evaporation & runoff

IrrigationCalculator.calculationHeading

IrrigationCalculator.calculationText

IrrigationCalculator.formulaLine1

IrrigationCalculator.formulaLine2

IrrigationCalculator.calculationDescription

IrrigationCalculator.efficiencyHeading

System	Efficiency	Main losses

IrrigationCalculator.useCasesHeading

IrrigationCalculator.faqHeading

IrrigationCalculator.ctaHeading

IrrigationCalculator.ctaDescription

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