Almond Irrigation Guide

Effective almond irrigation scheduling requires matching water applications to orchard development, atmospheric demand, root-zone conditions, and irrigation-system capacity. For commercial growers, decisions also need to account for salinity, nutrient uptake, harvest operations, and the effect of water stress on the following season’s production.

This guide explains how to calculate almond water requirements, interpret crop coefficients, determine irrigation duration, and coordinate fertigation with growth stages. Numerical examples are provided to illustrate the calculations. Actual schedules must be adjusted to the orchard’s age, canopy cover, soil, water quality, weather, and measured tree response.

Calculate almond water requirements using ET₀ and Kc

Reference evapotranspiration (ET₀) represents atmospheric evaporative demand. The crop coefficient (Kc) adjusts this reference to estimate orchard evapotranspiration (ETc):

ETc (mm/day) = ET₀ (mm/day) × Kc

The selected Kc must reflect orchard age, canopy development, season, ground cover, and the reference ET method used. Almond Kc is not a constant throughout the year.

Example: daily irrigation requirement

Assume a well-developed almond orchard has ET₀ = 6.0 mm/day and an applicable Kc = 0.95. The resulting ETc is:

ETc = 6.0 × 0.95 = 5.7 mm/day

Because 1 mm over 1 hectare equals 10 m³, the estimated consumptive water use is 57 m³/ha/day, or 399 m³/ha over seven days. This is estimated crop water use, not automatically the irrigation volume: effective rainfall, changes in stored soil water, irrigation efficiency, and any justified leaching requirement must also be considered.

Crop coefficients differ between young and mature orchards

Research on young almond orchards in California reported the following observed midseason crop coefficients. These values show why applying a mature-orchard Kc to a newly planted block may substantially overestimate demand.

Source: Drechsler, Fulton, and Kisekka (2022), measured values from specific California orchards. The table is for illustration, not a universal age-based Kc schedule.

Example almond crop coefficients by growth stage

The following crop coefficients illustrate how almond water demand changes through initial establishment, juvenile development, and the recurring production cycle. These are example baseline Kc values configured by growth stage, rather than universal coefficients for every orchard. In yieldsApp, Kc is interpolated linearly between successive growth-stage values, producing a gradual change in calculated ETc instead of an abrupt step at each stage transition.

For example, at ET₀ = 6.0 mm/day, Kc = 0.60 corresponds to ETc = 3.6 mm/day (36 m³/ha/day), while Kc = 1.10 corresponds to 6.6 mm/day (66 m³/ha/day). These calculations show the effect of different coefficients; actual daily Kc depends on the crop’s position within the stage, and the coefficients should be calibrated to orchard age, canopy cover, climate, and local observations.

Baseline crop Kc versus irrigation strategy: The values above describe the baseline crop-coefficient curve. A separate irrigation model may use adjusted Kc values to set a reduced irrigation target, for example during regulated deficit irrigation around hull split. That adjustment represents an irrigation-management decision and should not be confused with the baseline estimate of crop water demand.

Convert crop demand into irrigation runtime

Once the required net irrigation depth is determined, calculate the gross application using a justified field application-efficiency factor. For example, where a measured and appropriate application efficiency of 90% applies:

Gross irrigation depth = Net irrigation depth / 0.90

If the planned net irrigation requirement is 5.7 mm/day, the gross application becomes 6.33 mm/day, or approximately 63.3 m³/ha/day. The 90% value is illustrative; field efficiency must be verified and must not be confused with distribution uniformity. Where salinity requires leaching, evaluate the additional water requirement separately to avoid double-counting losses.

Example: calculate drip-irrigation hours

Consider an orchard planted at 6 × 5 m, with two drip lines per row, emitters every 0.75 m along each line, and an actual measured discharge of 2 L/hour per emitter.

• Emitters per hectare = (10,000 / 6) × (2 / 0.75) = approximately 4,444 emitters.
• System flow = 4,444 × 2 / 1,000 = approximately 8.89 m³/ha/hour.
• Runtime for 63.3 m³/ha = 63.3 / 8.89 = approximately 7.1 hours.

The calculation assumes all emitters operate at the measured discharge. Confirm flow rates, pressure, wetted distribution, and infiltration in the field. A single long irrigation may be inappropriate on coarse-textured or shallow soil, even when the total applied volume is correct.

Use soil water storage to set irrigation frequency

Daily ETc estimates the rate of crop water use. The root zone determines how much water can be withdrawn before irrigation is required. A basic estimate of total available water (TAW) is:

TAW (mm) = (Field capacity − Permanent wilting point) × Effective root-zone depth (m) × 1,000

Field capacity and permanent wilting point are volumetric water contents expressed in m³/m³. If the difference is 0.12 and effective rooting depth is 0.45 m, TAW is 54 mm. At a provisional management allowable depletion of 35%, the usable depletion before a planned refill is 18.9 mm.

At ETc = 5.7 mm/day and with no effective rainfall, 18.9 / 5.7 gives an approximate 3.3-day interval. This is only a starting estimate: active roots may occupy a smaller wetted volume than the full hectare, and actual irrigation timing should be verified with sensors and tree-water-status observations.

Adjust irrigation during critical almond growth stages

Establishment and vegetative growth

Young trees have small root systems and limited soil water reserves. They often need smaller and more frequent applications than mature orchards. During spring canopy development and fruit set, avoid sustained deficits that limit leaf area and developing crop potential. In mature orchards, monitor atmospheric demand alongside root-zone depletion and midday stem water potential.

Kernel development and hull split

During kernel development, prolonged water deficits may reduce kernel size or affect future production. Near hull split, some commercial programs use regulated deficit irrigation (RDI) to manage hull rot and water use. This practice requires close observation of tree stress and a clearly defined recovery strategy.

In a five-year California field experiment, maintaining midday stem water potential at approximately −14 to −18 bar (−1.4 to −1.8 MPa) during hull split reduced water use without a statistically significant reduction in yield, although average kernel weight was slightly lower. This is evidence from a particular experimental strategy, not a universal target or automatic irrigation cutoff. Cultivar, soil storage, climate, crop load, and monitoring capacity determine whether the approach is appropriate.

Harvest and postharvest

Harvest machinery may require a temporary reduction in irrigation, but prolonged water stress can affect bud development and next season’s productivity. Resume irrigation according to measured tree and soil conditions, remaining leaf activity, and the seasonal weather pattern. A postharvest budget should be part of the annual irrigation plan rather than an unplanned allocation of leftover water.

Manage salinity in the active root zone

Almond is sensitive to salinity. A commonly cited threshold for soil salinity measured in the saturated-paste extract (ECe) is approximately 1.5 dS/m. This is a soil-extract threshold, not an irrigation-water EC threshold. Actual response also depends on cultivar, rootstock, ion toxicity, drainage, and exposure duration.

Measure irrigation-water electrical conductivity (ECw), chloride, sodium, calcium, magnesium, bicarbonate, and other relevant quality indicators. Analyze soil salinity at multiple depths and lateral positions relative to the emitter because drip irrigation creates nonuniform salt distribution. Where salts accumulate, determine whether rainfall or planned leaching can remove them and verify that drainage is adequate.

For example, an irrigation-water EC of 1.2 dS/m and a soil ECe of 2.4 dS/m describe different measurements; they should not be compared directly against the same 1.5 dS/m threshold. Monitor the trend in ECe and assess chloride and sodium injury separately. For sampling and interpretation, see irrigation water quality testing.

Coordinate almond fertigation with water demand and crop yield

Irrigation scheduling influences the distribution and recovery of fertilizer. Nitrogen and potassium requirements should be determined from realistic yield objectives, nutrient removal, tree reserves, soil supply, and analytical results. A crop-uptake reference is useful for planning, but it should not automatically be treated as the required fertilizer application rate.

Example: nutrient reference for an almond yield of 1 t/ha

The following values are taken from the Brookside reference shown in the supplied yieldsApp configuration, at a stated reference yield of 1 t/ha. They are illustrative configuration inputs, not independently verified uptake standards. Values are expressed in the nutrient forms shown in that reference.

Interpretation matters: nutrient uptake includes nutrients accumulated in different plant tissues, whereas nutrient removal represents nutrients exported from the production system according to the underlying reference definition. Neither number alone establishes the amount of fertilizer needed. Before using the table operationally, confirm whether the 1 t/ha yield is measured as kernel yield or another commercial yield basis, and verify the analytical basis and units for each element.

Example: distribute seasonal nitrogen by stage

In the supplied example, a configured nutrient-distribution program assigns 15% to establishment, 35% to early vegetative growth, and 50% to vegetative growth. Applied to the reference nitrogen uptake of 78 kg N/ha, this gives:

These amounts represent a mathematical distribution of the configured uptake reference, not an endorsed almond fertilizer program. In particular, establishment and early vegetative stages in a young orchard should not automatically be combined with a yield-based bearing-tree reference. Separate distributions may be needed for nitrogen, phosphorus, potassium, and other nutrients because their uptake dynamics differ.

Actual fertilizer supply must account for nutrient contributions from irrigation water, soil mineralization, existing soil reserves, residual fertilizer, and estimated recovery efficiency. Inject fertilizer only when application timing and irrigation duration support placement within the active wetted root zone. A practical sequence is to start irrigation, inject during a controlled middle portion of the set, and allow enough clean water afterward to clear the lines and position nutrients appropriately. Use soil and leaf analysis to review the program.

Build a repeatable almond irrigation decision process

For each orchard block, record orchard age, cultivar, rootstock, soil characteristics, effective root depth, emitter design, measured system flow, irrigation-water quality, yield objective, and the selected Kc model. Update irrigation requirements from local ET₀, effective rainfall, measured soil moisture, and tree-water-status observations.

A useful weekly review answers four operational questions: How much water did the orchard require? How much was actually delivered? Did it reach the intended root zone? Did the trees respond as expected? Deviations should trigger specific actions, such as adjusting runtime, inspecting clogged emitters, checking drainage, or revising irrigation timing before a forecast heat event.

For organizations coordinating multiple orchards and growers, yieldsApp can support consistent crop parameters, field-level protocols, water and nutrient plans, and follow-up on agronomic recommendations. Capturing actual execution alongside the planned schedule helps technical teams identify recurring deviations, investigate causes, and standardize corrective actions across distributed operations.

Common almond irrigation mistakes

• Using one Kc curve for all orchards: young blocks, mature blocks, and orchards with different canopy cover can have substantially different water demands.
• Confusing ETc with the volume to pump: rainfall, stored soil water, application efficiency, and salinity management must be considered.
• Setting irrigation runtime from nominal emitter discharge: measure actual flow and inspect pressure variation and distribution uniformity.
• Reducing water at hull split without measuring stress: excessive deficits can affect kernel development and subsequent production.
• Equating nutrient uptake with fertilizer demand: account for soil and water contributions, nutrient removal, nutrient recovery, and the true yield basis.
• Ignoring the location of salts: assess salinity throughout the wetted root zone, not from a single unrepresentative sample.

Key takeaways

Reliable almond irrigation management begins with a defensible estimate of crop demand, then uses soil and tree measurements to verify what is happening in the orchard. Crop coefficients must reflect orchard development. Runtime must be calculated from measured irrigation-system output. Salinity and nutrient management must be coordinated with water delivery, particularly when water supplies are constrained. Consistent block-level records make those decisions more accurate and repeatable across seasons.

Technical references

• Drechsler, Fulton and Kisekka (2022). Crop coefficients and water use of young almond orchards. Irrigation Science.
• Stewart et al. (2011). Regulated deficit irrigation reduces water use of almonds without affecting yield. California Agriculture.
• UC Agriculture and Natural Resources. Managing Salts by Leaching, Publication 8550.