Young and Mature Orchard Irrigation and Chemigation Calculator

Irrigation need from ETc

Enter mature-orchard ETc for the irrigation period. Select the crop. Tree age appears only for almond or walnut. Other crops are treated as mature trees with no age adjustment.

Adjusted ETc = mature ETc × the crop/tree-age adjustment. Irrigated acres = total area × wetted area %. Irrigation depth to apply = net irrigation ÷ application efficiency.
Use this as a planning estimate. Check and adjust the recommendation with soil moisture sensors, field observations, and plant-based methods such as stem water potential, pressure chamber readings, microtensiometers, or canopy/leaf water-stress observations.

Irrigation run time

Estimate how long to run the system to apply a target net irrigation depth over the wetted/irrigated portion of the orchard. Application efficiency is used to estimate the gross depth and total runtime.

Gross depth needed = target net depth ÷ application efficiency. Runtime = gross depth × irrigated acres × 27,154 gallons per acre-inch ÷ system flow rate.
Confirm run time with actual pressure, flow meter readings, emitter output, distribution uniformity, soil moisture sensors, and plant-based stress measurements.

Alternative run time by gallons per tree and emitter output

Use this method for drip or microsprinkler systems when you know emitter output and emitter spacing.

Gallons per tree = ETc × row spacing × tree spacing × 0.623. Emitter output per tree = one emitter's output × (tree spacing ÷ space between each emitter). Hours of irrigation = gallons per tree ÷ emitter output per tree.

Water application rate

Calculate the water application rate from flow rate and irrigated area.

Water application rate = flow rate ÷ irrigated area. The calculator converts the result to inches/hour, inches/day, mm/hour, and mm/day.

Convert weekly ET estimates to gallons per tree

Convert a weekly ET estimate reported as inches per acre into gallons per tree using tree spacing.

Net gallons per tree = ET inches × tree spacing × row spacing × 0.623. Gross gallons per tree = net gallons per tree ÷ application efficiency.
Use crop ET for the correct crop and orchard age. For young orchards, use an ET estimate already adjusted for canopy or tree age before using this conversion.

Water applied

Use this after irrigation to estimate gross and net depth applied.

Gross depth = flow × hours × 60 ÷ 27,154 ÷ irrigated acres. Net useful depth = gross depth × application efficiency.

Irrigation frequency

Estimate maximum interval between irrigations using daily ETc, available water, root depth, and allowable depletion.

Frequency = (available water holding capacity × root depth × allowable depletion) ÷ daily ETc.
Use shorter intervals when soil sensors, pressure chamber readings, microtensiometers, or field observations show crop water stress before the calculated interval.

Chemigation: chemical injection rate by volume

Use when the recommendation gives a liquid product rate by area.

Injection rate = total chemical volume ÷ injection time.
Always follow the product label. Confirm compatibility, backflow prevention, agitation, system uniformity, PPE, and local regulations before chemigation.

Chemigation: chemical injection rate by mass

Use when the recommendation is mass per area and the injected solution concentration is known.

Total mass = application rate × area. Solution volume = total mass ÷ solution concentration. Injection rate = solution volume ÷ injection time.
Confirm whether the recommendation is product weight, nutrient weight, or active ingredient weight.

Chemigation: injection rate for water chemistry control

Estimate injection rate needed to maintain a desired active ingredient concentration in irrigation water.

Injection rate, gph = water flow, gpm × desired ppm × 60 ÷ (10,000 × active ingredient % × specific gravity).
Use only products labeled for injection. Check water chemistry, emitter compatibility, crop safety, and safety requirements before injecting acids or oxidizers.

Maximum solution concentration in irrigation lines

Estimate solution concentration in the irrigation line from chemical injection rate and irrigation water flow rate.

Solution concentration, % = injection flow rate ÷ irrigation water flow rate × 100. Both flows are converted to gallons per hour.
Do not exceed label concentration limits or crop safety thresholds.

Mixing dry chemicals

Estimate dry product needed when target application rate and product concentration are known.

Dry product weight = target chemical mass ÷ product concentration fraction.
Check whether the label rate is active ingredient, nutrient, or total product.

Batch/bulk application

Calculate injection rate for a known batch or bulk chemical volume and injection time.

Injection rate = batch volume ÷ injection time.

Minimum batch volume

Estimate minimum water volume needed to dissolve a dry chemical based on solubility. Adding more than the calculated minimum is often needed for handling and mixing.

Minimum added water = dry chemical weight ÷ solubility.
Confirm solubility from the label or fertilizer solution chart. Add water slowly, agitate, and follow safety requirements.

Injection pump calibration

Estimate how long it should take the injection pump to fill a container if the pump is delivering the desired rate.

Fill time = container volume ÷ pump injection rate.
If the container fills faster than this time, the pump is injecting too fast. If it fills slower, the pump is injecting too slowly.

Planning aid only. Results should be checked against field measurements, system calibration, pressure and flow measurements, product labels, crop conditions, soil moisture sensors, and plant-based water-stress methods.