WaterCalcLabIrrigation Frequency Planner
Estimate root-zone depletion time using a simplified FAO-56 soil-water balance.
Your result
Bars compare only results in the same unit group. They are normalized, not a time-series forecast.
Planning result based on your inputs.
How this tool works
Estimate root-zone depletion time using a simplified FAO-56 soil-water balance.
TAW = AWC × root depth; RAW = p × TAW; days = RAW/(ET₀ × Kc)Example calculation
The prefilled form is a worked example. Its base-unit inputs and expected outputs are shown below; use the reset button to restore it.
| Input | Example |
|---|---|
| Available soil water per metre | 150 |
| Effective root depth | 0.3 |
| Allowable depletion fraction p | 0.5 |
| Reference evapotranspiration ET₀ per day | 4 |
| Crop coefficient Kc | 0.8 |
Frequently asked questions
How should I choose the inputs?
Use measurements and local records for the stated period. All preset values are illustrative examples, not recommendations.
What does this result leave out?
Starts at field capacity and assumes constant ET, no rain or capillary rise. Use measured soil moisture and crop-specific p; this is not an automatic schedule.
Continue your plan
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Method version 1.0 · Last reviewed: 2026-10-10