Enter the soil holding capacity, root zone depth, allowable depletion, and crop water use rate into the calculator to determine the irrigation interval.

Irrigation Frequency/Interval Formula

The following equation is used to calculate the Irrigation Frequency/Interval.

IF = SHC * D * (AD/100) / CU
  • Where IF is the irrigation frequency (day)
  • SCH is the soil holding capacity (in/ft)
  • D is the root zone depth (ft)
  • AD is the allowable depletion percentage
  • CU is the crop water use rate (in/day)

What is an Irrigation Frequency/Interval?


An irrigation frequency is a the recommended number of days in between irrigation that should be followed for maximum crop growth.

How to Calculate Irrigation Frequency/Interval?

Example Problem:

The following example outlines the steps and information needed to calculate the Irrigation Frequency.

First, determine the soils water holding capacity. In this example, the holding capacity of the soil is 5 in/ft.

Next, determine the root zone depth. This is measured to be 3 ft.

Next, determine the allowable depletion. This is calculated to be 50%.

Next, determine the crop water use rate. This is measured to be 2 inches per day.

Finally, calculate the irrigation frequency using the formula above:

IF = SHC * D * (AD/100) / CU

IF = 5 * 3 * (50/100) / 2

IF = 3.75 days