Steps To Design An Irrigation Schedule For North Dakota Climate

Designing an effective irrigation schedule for North Dakota requires integrating local climate patterns, crop water needs, soil properties, irrigation system capabilities, and management goals. This article walks through a clear, step-by-step process with concrete calculations, practical rules of thumb for North Dakota conditions, monitoring options, and a short decision checklist you can apply to field crops, forage, and turf in the state.

Understand North Dakota climate and irrigation season characteristics

North Dakota has a continental climate with cold winters, a short but intense growing season, variable summer rainfall, and frequent winds. Key implications for irrigation scheduling:

• The irrigation season is generally concentrated between late May and early September, although start and end dates depend on local frost dates and crop stage.
• Reference evapotranspiration (ETo) is low in spring, peaks in mid-summer, and drops in late summer and fall. Peak daily ETo in central and eastern North Dakota often ranges from about 0.18 to 0.30 inches per day in June-July, depending on temperature, wind, and humidity.
• Rainfall is often variable and occurs in storms. Effective rainfall (the portion that replenishes root-zone moisture) must be estimated rather than assumed equal to measured rainfall.
• Soils are diverse: glacial tills, silt loams, loams, and clay loams are common. Soil water holding capacity and infiltration rates vary accordingly.

Understanding these general patterns allows you to size and time irrigation events to match crop demand and avoid overtreatment or water stress.

Step 1 — Define objectives, crop, and management allowance

Start by answering three questions:

• What crop or landscape are you irrigating? (for example: corn, soybean, spring wheat, sugar beet, alfalfa, pasture, or turf)
• What is your acceptable level of soil moisture depletion before irrigating? (management allowable depletion, MAD: e.g., 50% for many annual row crops, 30% for perennials or high-value crops, 20-30% for turf)
• Are you prioritizing yield maximization, water conservation, or risk reduction (insurance)?

These choices determine how often and how much you will irrigate.

Step 2 — Determine crop water use (ETc)

Calculate crop evapotranspiration (ETc) as:
ETc = ETo x Kc
Where:

• ETo is reference evapotranspiration (in/day), ideally from local weather station data or regional estimates based on Penman-Monteith or similar methods.
• Kc is the crop coefficient that varies with crop type and growth stage (early season, mid-season peak, late season).

North Dakota practical ranges and examples:

• Typical ETo by season (approximate): May 0.10-0.15 in/day; June 0.15-0.22 in/day; July 0.18-0.30 in/day; August 0.15-0.22 in/day; September 0.10-0.16 in/day.
• Representative Kc values:
• Corn: early 0.3-0.6, mid 1.10-1.20, late 0.6-0.8.
• Soybean: early 0.3-0.6, mid 1.05-1.15, late 0.5-0.8.
• Spring wheat: early 0.4-0.7, mid 0.9-1.05, late 0.5-0.8.
• Alfalfa: mid-season Kc near 1.15-1.25.

Example calculation (practical):

• Mid-July corn: ETo = 0.25 in/day, Kc = 1.15 – ETc = 0.2875 in/day.

Use daily ETc and sum over your desired irrigation interval to estimate water requirement between irrigations.

Step 3 — Quantify soil available water and rooting depth

Estimate available water in the crop root zone:
Available water (inches) = AWHC (inches per foot) x effective root depth (feet)
Typical available water holding capacity (AWHC) by soil texture (approximate):

• Sand / very coarse: 0.5-0.75 in/ft
• Sandy loam: 0.8-1.2 in/ft
• Loam / silt loam: 1.4-2.0 in/ft
• Clay loam: 1.2-1.6 in/ft

Typical root depth guidance:

• Corn: 2.5-4.0 ft (use 3.0 ft as common design depth)
• Soybean: 2.0-3.0 ft
• Spring wheat: 2.0-3.0 ft
• Alfalfa: 3.0-4.0 ft
• Turf: 0.75-1.5 ft

Example:

• Loam soil AWHC = 1.6 in/ft; corn root depth = 3.0 ft – Available water = 4.8 inches.

Step 4 — Choose management allowable depletion (MAD) and compute net irrigation depth

Decide the fraction of available water you will allow the crop to use before irrigation:

• Annual row crops: MAD 0.40-0.60 (50% is common)
• Perennial forages, high-value crops: MAD 0.30-0.40
• Turf/greens: MAD 0.20-0.30

Compute the target refill amount when soil has been depleted to MAD:
Net irrigation depth needed to refill to field capacity (inches) = ETc over interval + refill to bring soil back to MAD
A simpler operational approach is:

1. Determine ETc over the irrigation interval (days between irrigations) and any effective rainfall that occurred.
2. If the cumulative ETc minus effective rainfall exceeds the usable water above the chosen MAD, apply irrigation to refill to the chosen MAD — or fully refill depending on management.

Example calculation with numbers:

• Crop: corn in July.
• ETc = 0.2875 in/day.
• Interval: 7 days – crop water use = 2.0125 in.
• Soil available water = 4.8 in (from prior example).
• MAD = 0.5 – usable water before refill = 4.8 x 0.5 = 2.4 in.

Interpretation: The 7-day crop use (2.01 in) is less than the allowed depletion (2.4 in), so you could wait a bit longer. If you prefer to irrigate when approaching MAD, schedule before the cumulative ETc exceeds 2.4 in.
If cumulative ETc had been 3.0 in, required net refill = 3.0 in to restore down to the MAD. If you want to refill to full available water, irrigate 3.0 in plus the difference to reach field capacity.

Step 5 — Convert net irrigation to gross irrigation using system efficiency

No irrigation system applies water with 100% uniformity. Convert the net depth to the gross application by dividing by system efficiency (accounting for deep percolation losses, wind drift, evaporation, uneven distribution).
Common field efficiency estimates:

• Drip / subsurface drip: 85-95%
• Low-elevation spray/dripline: 80-90%
• Modern center pivot, well-maintained: 75-85%
• Traditional flood/surface: 50-70%

Gross irrigation depth (inches) = Net depth (inches) / Application efficiency
Example:

• Needed net irrigation = 2.01 in
• System efficiency = 0.80 (80%) – gross = 2.01 / 0.80 = 2.51 in

Subtract effective rainfall that occurred during the period; if 0.5 in effective rain fell, gross required becomes 2.01 – 0.5 = 1.51 in net – gross 1.51 / 0.8 = 1.89 in.

Step 6 — Translate irrigation depth to run time for your system

Determine the precipitation rate (inches per hour) of your irrigation system for the area being watered. Most system manuals or flow measurements yield an application rate.
Run time (hours) = Gross irrigation depth (inches) / System precipitation rate (inches per hour)
Practical notes for North Dakota:

• Avoid very long continuous runs under high winds; break into multiple shorter sets to reduce drift and evaporation losses.
• Apply in the coolest part of the day (early morning) to minimize evaporation and improve infiltration. Avoid late-evening applications for crops at high disease risk unless required.

Step 7 — Monitoring: soil moisture and crop indicators

Combine ET-based scheduling with direct monitoring for best results.
Soil-based monitoring options:

• Capacitance or TDR probes: provide volumetric water content (%). Use sensors at multiple depths within the root zone.
• Tensiometers: measure soil matric potential; useful in fine to medium-textured soils.
• Manual soil probe: feel and look for moisture; economical and practical for small fields.
• Neutron probe and gravimetric sampling: accurate but more expensive and labor intensive.

Plant-based indicators:

• Leaf rolling, wilting, or slowed growth indicate stress but are late indicators.
• Stomatal conductance and canopy temperature sensors can detect stress earlier.

Record keeping:

• Keep daily or weekly ETc estimates, precipitation totals (and estimated effective rainfall), irrigation events (date, depth applied), and soil moisture readings.

Monitoring frequency:

• During rapid growth or heat waves, check soil moisture weekly or more often.
• During cool, low ET periods, biweekly checks may be sufficient.

Step 8 — Adjust for rainfall, extreme weather, and seasonal changes

• Estimate effective rainfall: small storms or heavy downpours on dry soil can generate runoff and result in lower effective infiltration. As a rule of thumb, assume 60-80% of moderate rain is effective; adjust based on soil infiltration capacity and storm intensity.
• During heat waves with elevated ETo, shorten irrigation interval or increase applied depth.
• Late-season: reduce irrigation as crops senesce and Kc decreases. Avoid unnecessary irrigation after physiological maturity.
• Frost risk: in early spring or late fall, avoid irrigation close to freezing nights that can create icy conditions or damage.

Special considerations for North Dakota

• Wind: frequent winds increase ETo and reduce sprinkler uniformity; consider lower-pressure nozzles, windbreaks, or switching to lower-exposure application methods (center pivot drop tubes, low-elevation applicators, or subsurface drip).
• Short growing season: early planting and timely irrigation can be critical. However, do not overwater in spring when soils are cold; that delays warming.
• High infiltration soils: on well-drained silt or sandy soils, apply smaller, more frequent doses to avoid deep percolation losses.
• Heavy clay soils: apply slower rates to avoid runoff and puddling; longer intervals with larger events may be appropriate if infiltration is slow, but watch for crusting.

Example operational checklist (practical takeaways)

• Identify crop, current growth stage, and Kc.
• Obtain local ETo daily values (from your on-farm weather station or local reports).
• Determine soil texture, AWHC per foot, and effective root depth.
• Choose MAD based on crop and management goals.
• Calculate ETc for your planned interval, subtract effective rainfall, and compare to usable soil water.
• Compute net irrigation need and adjust for application efficiency to get gross depth.
• Translate gross depth into run time for your irrigation system, considering wind and infiltration.
• Monitor soil moisture and crops weekly during critical periods; adjust schedule based on observations and records.

Final recommendations and best practices

• Use a combined approach: ET-based scheduling augmented by soil moisture sensors gives the best control.
• Start the season conservatively: do not over-irrigate cold soils in spring; let soils warm and seedlings establish.
• Keep good records: irrigation logs and soil moisture history will make future seasons easier to manage.
• Maintain equipment: check uniformity, nozzle wear, leaks, and pressure to preserve application efficiency.
• Calibrate rainfall gauges and soil sensors regularly.
• Consider system upgrades (low-pressure sprinklers, drop hoses, or drip) if wind and distribution uniformity are recurring issues.

Designing an irrigation schedule for North Dakota involves blending climatology, crop physiology, soil physics, and system hydraulics into a coherent, monitored plan. Applying the steps above with local data and regular field checks will optimize water use, protect yield, and reduce risk across variable North Dakota seasons.