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 — Daily Water Need & Run Time | LandLens

Calculate daily crop water requirements using ET\u2080 and crop coefficients. Get total volume, system run time, and efficiency for drip, sprinkler, or flood irrigation.

IrrigationCalculator.climateEt0

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IrrigationCalculator.fieldArea

≈ 10,000 m²

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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

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IrrigationCalculator.calculationDescription

IrrigationCalculator.efficiencyHeading

System	Efficiency	Main losses

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IrrigationCalculator.ctaDescription

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