Irrigation Depth per Application Calculator

About the Irrigation Depth per Application Calculator

When you irrigate, not all water applied reaches the crop's root zone. Some is lost to evaporation, wind drift, deep percolation, or runoff. The gross irrigation depth accounts for these losses so that the net amount actually needed by the soil is delivered.

The relationship is straightforward: gross depth equals net depth divided by application efficiency. If your system is 80% efficient and the soil needs 1.0 inch of water, you must apply 1.25 inches gross. Knowing this number lets you set run times, flow rates, and pivot speeds correctly.

This calculator converts your target net irrigation depth into the gross depth your system must deliver, given its measured or estimated application efficiency. It also shows the volume in gallons per acre for operational planning. Use it when converting soil-water targets into the gross depth your pivot, set, or drip block must actually deliver in the field.

When This Page Helps

Applying the wrong depth wastes water and energy or leaves your crop short. This page helps you turn a root-zone target into a gross application depth you can actually program at the pump panel, pivot control, or set time sheet.

How to Use the Inputs

1. Enter the net irrigation depth your soil needs in inches.
2. Enter your system's application efficiency as a percentage.
3. Read the gross depth your system must apply.
4. Review the gallons per acre needed.
5. Use the gross depth to calculate run times or pivot speed.
6. Adjust efficiency if you have measured values from catch-can tests.

Example Calculation

Tips & Best Practices

• Center pivots typically achieve 80–90% application efficiency.
• Drip systems can reach 90–95% efficiency.
• Furrow irrigation efficiency is often only 50–70%.
• Perform catch-can tests to measure actual efficiency.
• Wind and high temperatures reduce sprinkler efficiency.
• Low-pressure drop nozzles and LEPA systems improve efficiency.

Efficiency by System Type

Surface irrigation (flood, furrow, border) ranges from 40–75% efficiency. Sprinkler systems (hand-move, wheel-line, center pivot) range from 65–90%. Drip and micro-irrigation achieve 85–95%. Choosing a higher-efficiency system reduces gross water requirements but involves higher capital costs.

Running the Catch-Can Test

Place at least 16–24 cans in a grid pattern across one span or set of the system. Run the system for its normal duration. Measure the depth in each can with a graduated cylinder. Average the values and divide by the applied depth (from flow meter or nozzle charts) to get application efficiency.

Linking Depth to Run Time

Once you know the gross depth, divide it by the system's application rate (in/hr) to get run time. For center pivots, convert depth to rotation speed (% timer setting). For drip, multiply depth by area per emitter to get run time per zone.

Frequently Asked Questions

• What is application efficiency?

  Application efficiency is the fraction of water applied that is stored in the root zone and available for crop use. It accounts for evaporation, drift, deep percolation, and runoff losses.

• How do I measure application efficiency?

  The catch-can test is the most common field method. Place cans at regular intervals under the irrigation system, run it for a set time, and measure the water collected. Compare collector averages to the applied depth.

• What is a typical net depth?

  Net depth depends on MAD and soil AWC. For a silt loam with 1.8 in/ft AWC and 3 ft roots at 50% MAD, the net depth is 2.7 inches. Lighter irrigations may target 0.5–1.5 inches.

• Does gross depth include conveyance losses?

  No. Conveyance losses (canal seepage, pipe leaks) are separate. Overall system efficiency = conveyance efficiency × application efficiency. This calculator addresses application efficiency only.

• How does wind affect efficiency?

  Wind speeds above 10 mph can reduce sprinkler efficiency by 10–20% due to drift and increased evaporation. Irrigating at night or using low-angle nozzles reduces wind losses.

• Why not just assume 100% efficiency?

  No real-world system achieves 100%. Ignoring losses leads to under-irrigation and crop stress. Using measured efficiency ensures the soil actually receives the intended amount of water.