Calculate how often to irrigate by dividing net application depth by daily crop ETc. Determine the interval in days between irrigations.
Irrigation frequency tells you how many days you can wait between irrigation events before the crop experiences stress. It is calculated by dividing the net depth of water applied per irrigation by the daily crop evapotranspiration (ETc). A deeper application or lower ETc extends the interval; shallower irrigations or higher demand shortens it.
Knowing irrigation frequency helps you plan labor, coordinate multiple fields, schedule pumping, and ensure your system has the capacity to cover all fields within the required rotation. If the frequency is shorter than the time needed to complete a full rotation, you need either a faster system or reduced acreage per system.
This calculator provides the irrigation interval in days, the number of irrigations per season, and the total seasonal water volume so you can budget water rights and energy costs. Whether you are a beginner or experienced professional, this free online tool provides instant, reliable results without manual computation.
Incorrect irrigation frequency is a common source of yield loss. Too infrequent irrigations allow soil moisture to drop below the stress threshold. Too frequent irrigations waste water and energy. This tool helps you match your system's capacity to the crop's actual need. Having a precise figure at your fingertips empowers better planning and more confident decisions.
Interval (days) = Net Application Depth (in) / Daily ETc (in/day) Irrigations per Season = Season Length / Interval Total Seasonal Depth = Irrigations × Net Depth
Result: Interval = 5.0 days; 24 irrigations/season
Interval = 1.5 / 0.30 = 5.0 days. Over a 120-day season, you need 120 / 5 = 24 irrigations. Total net depth = 24 × 1.5 = 36 inches.
System capacity is measured in gallons per minute (GPM) and determines how quickly you can apply a given depth across your acreage. If peak-demand frequency requires more irrigations than the system can complete, you face a capacity shortfall. Solutions include increasing pump output, adding a second system, or deficit-irrigating non-critical stages.
Modern variable-rate center pivots can adjust application depth by zone, matching soil variability within a field. Zones with sandier soil receive lighter, more frequent irrigations while clay zones receive deeper, less frequent applications — all in a single revolution.
Irrigation frequency is a planning number; actual scheduling uses the soil water balance. Frequency tells you the expected pattern, while the balance tracks real-time depletion. If rain delays an irrigation, the balance shows you exactly when to resume.
An interval below 1 day means your net depth per irrigation is insufficient to meet daily ETc. Increase the application depth or switch to a system that can apply water continuously, such as drip.
After effective rainfall, subtract it from the cumulative depletion. This extends the time before the next irrigation is needed. Reset your interval calculation based on the new depletion level.
No. ETc changes with growth stage and weather. Recalculate the interval at least monthly or whenever you update Kc values for a new growth stage.
During peak demand in midsummer, corn ETc can reach 0.30–0.35 in/day. With 1.5 in net per irrigation, the interval is 4–5 days. Early and late season intervals may be 7–10 days.
Yes, but more frequent irrigations with smaller depths increase evaporation losses and may keep the soil surface wet, encouraging disease. The calculated interval based on MAD is the optimal target.
If your center pivot takes 3 days to complete a revolution and the required interval is 5 days, you have margin. If required interval drops to 2 days during peak demand, the system cannot keep up.