Start / Water and irrigation / Irrigation management and depth
Enter the soil, crop, climate, and system to find out how often to irrigate, how much water to apply, and for how long.
Pre-sizing and estimating tool: the results do not replace a design, calculation, or report signed by a qualified professional, nor verification against the applicable standards.
Drying and refill cycle: the soil starts at field capacity, dries down to the limit without stress and is irrigated again.
The shorter the interval, the hotter and drier the climate; the dot marks the ET₀ you entered.
Drag the controls to simulate data different from what you entered (from 30% less to 30% more) and watch the result change instantly.
Days between irrigations for different reference evapotranspiration (ET0) and crop coefficient (Kc) values, with your soil's net depth.
The calculation done in steps, with the values you entered.
The calculation memo gathers this page's inputs, results, equations, assumptions, and references, with fields for project, responsible person, and review. The full report also includes the charts and interpretations, in color. In the print window, choose Save as PDF.
Enter the soil moisture at field capacity and at wilting point, the effective root depth, and the readily available fraction. Then add the period's reference evapotranspiration (ET0), the crop coefficient (Kc), the system efficiency, the flow rate, and the area irrigated at a time. The calculator returns the irrigation interval, the net and gross depths, the irrigation time, and the water volume.
Soil with 30% moisture at field capacity and 14% at wilting point, root depth of 600 mm, p = 0.5, ET0 of 5.5 mm/day, Kc = 1.0, 85% efficiency, flow of 300 m³/h over 10 ha.
ETc = 1.0 × 5.5 = 5.5 mm/day. CAD = (30 − 14) ÷ 100 × 600 = 96 mm. Net depth = 96 × 0.5 = 48 mm. Interval = 48 ÷ 5.5 = 8.7 days. Gross depth = 48 ÷ 0.85 = 56.5 mm. Rate = 300 ÷ (10 × 10) = 3 mm/h, so it is about 18.8 h and 5,647 m³ per irrigation.
Typical values for planning. Use your project data whenever available.
| System | Usual efficiency |
|---|---|
| Drip irrigation | about 90% |
| Center pivot | 80% a 85% |
| Conventional sprinkler irrigation | 70% a 80% |
| Surface (furrows and flooding) | 50% a 70% |
Drawing water for irrigation requires a water-use permit under the National Water Resources Policy. The volume per irrigation calculated here helps size the application and plan the use.
To add water and energy to the crop budget, use the production cost per hectare.
Divide the net depth the soil can refill (CAD × p) by the crop's daily evapotranspiration (Kc × ET0).
Because the system loses water during application. The gross depth is the net depth divided by efficiency.
It is the part of the available water that the crop can use without stress. Sensitive crops have a lower p, and tolerant ones a higher one; the values by crop are in the FAO-56 manual. Use the value for your crop.
From the nearest weather station, such as those of INMET, in mm/day. To size the system with margin, use the average of the hottest days in the period of highest demand.
In practice, yes. This calculator does not consider effective rain; on rainy days the interval lengthens, and the next irrigation should be reassessed with the soil moisture.
Because it must not exceed the soil's infiltration rate. High rates cause runoff and water loss; in that case, reduce the depth per pass or spread the flow over more area.
From the soil water retention curve, made in a lab, or from texture-based tables. Sandy soils hold less water than clay soils, and this changes the irrigation interval a lot.
Important notice: the Agrocalcs tools make estimates and preliminary sizing based on the data entered and on published engineering methods. They do not replace a design, a calculation report or a report signed by a qualified professional (CREA/ART), nor verification against the applicable technical standards and legislation, such as the Regulatory Standards of the Ministry of Labor. Material and fuel properties vary: check with the manufacturer or with analyses of your process before deciding. By using the site, you agree to the Terms of Use.
© 2026 Agrocalcs. Found an error? Write to contato@agrocalcs.com.br.