Inputs
Example Data
| Method | Inputs (selected) | Net depth (mm) | Gross depth (mm) @ 75% |
|---|---|---|---|
| Moisture deficit | FC 0.30, θi 0.22, Zr 0.60 m, Rain 0 | 48.00 | 64.00 |
| Allowable depletion | FC 0.30, WP 0.15, Zr 0.60 m, p 0.50 | 45.00 | 60.00 |
| ETc × interval | ETc 5.2 mm/day, Interval 7 days, Rain 5 | 31.40 | 41.87 |
Example values are illustrative and should be verified for local soils, crops, and field conditions.
Formulas Used
1) Moisture Deficit Method
Net(mm) = (FC − θi) × Zr(m) × 1000
where FC and θi are volumetric moisture contents.
2) Total Available Water (TAW) Method
TAW(mm) = (FC − WP) × Zr(m) × 1000
Net(mm) = p × TAW
where p is the allowable depletion fraction.
3) ETc Interval Method
Net(mm) = ETc(mm/day) × Interval(days)
Adjustments
- Effective rainfall:
Net = max(0, Net − Rain) - Leaching fraction (LF):
Net = Net / (1 − LF) - Design margin:
Net = Net × (1 + Margin/100) - Gross depth:
Gross = Net / (Ea/100)
How to Use This Calculator
- Select a calculation method based on your field data.
- Choose moisture input unit as fraction or percent.
- Enter the required method inputs and root zone depth.
- Add effective rainfall if you expect usable precipitation.
- Optionally include leaching fraction and a design margin.
- Provide application efficiency to estimate gross depth.
- Enter an area to convert depth into water volume.
- Press Calculate to view results above the form.
- Use the CSV or PDF buttons to export your output.
Professional Notes for Net Irrigation Depth
1) What the calculator solves
Net irrigation depth is the refill water needed to bring the effective root zone back toward a target moisture state. This page calculates a raw net requirement, subtracts effective rainfall, and optionally increases depth for salinity leaching and a design margin. Results are provided as depth (mm and inches) and as volume, including m³/ha and total m³ for an entered field area. Keep units consistent, and document assumptions for audits and future seasons clearly.
2) Data you should prepare
For soil-water methods, use volumetric moisture content from lab tests, calibrated sensors, or site-specific charts. Typical FC values range from 0.25–0.40, while WP often ranges 0.10–0.20, depending on texture. Root zone depth (Zr) commonly varies from 0.30 to 1.20 m by crop stage. If you lack moisture data, ETc and a scheduling interval can produce a practical planning estimate.
3) How outputs are computed
Moisture deficit uses (FC − θi) × Zr × 1000. The allowable depletion method first calculates TAW=(FC − WP) × Zr × 1000, then applies p×TAW, where p typically ranges 0.30–0.60 for many crops under standard management. ETc scheduling uses ETc × interval, then applies rainfall deduction. When leaching fraction is used, net depth increases by 1/(1 − LF).
4) Conversions that help reporting
Depth-to-volume conversion is direct: 1 mm across 1 hectare equals 10 m³. Therefore, 45 mm corresponds to 450 m³/ha. Inches are reported using 25.4 mm per inch. If you enter an area, the calculator multiplies depth (m) by area (m²) to return site volume. These conversions align field notes, tanker schedules, and pump-hour planning.
5) Interpreting net versus gross depth
Net depth represents beneficial water stored in the root zone. Gross depth estimates the applied water needed to deliver that net amount, using application efficiency (Ea). Typical Ea ranges are 60–75% for surface methods, 70–85% for well-managed sprinklers, and 85–95% for properly designed drip systems. Use gross depth for supply, pumping, and distribution sizing.
FAQs
1) What is “net irrigation depth” in practice?
It is the depth of water that must reach and be stored in the crop root zone to correct the moisture deficit after accounting for effective rainfall and planned adjustments.
2) When should I use the moisture deficit method?
Use it when you have reliable field capacity and current moisture measurements for the root zone, such as calibrated probes, gravimetric sampling, or validated soil-water curves.
3) How do I choose the allowable depletion factor p?
p depends on crop sensitivity and climate demand. Many practical designs use 0.30–0.60. Use lower p for sensitive crops or hot periods, and higher p when stress tolerance is acceptable.
4) What does “effective rainfall” mean here?
It is the portion of rainfall that is stored in the root zone and reduces irrigation need. Losses due to runoff, interception, and deep percolation are excluded.
5) Why include a leaching fraction?
Salinity control may require extra percolation below the root zone. The leaching fraction increases net depth to help maintain acceptable salinity levels for soil and crop conditions.
6) Why are gross depths larger than net depths?
Field systems lose water through non-uniformity, evaporation, runoff, or deep percolation. Gross depth divides net depth by application efficiency to estimate the delivered application requirement.
7) Can I use this for pump sizing and scheduling?
Yes. Use gross volume for supply planning, then convert to pump run time using discharge capacity. Always verify constraints such as infiltration rate, allowable set time, and operational windows.