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Regional Calendars, Climate & DataIrrigation Needs by Region and Crop
Irrigation need depends on the crop, its growth stage, the weather and the soil, not on region alone. A simple water balance gives you a method you can adapt anywhere.
Key points
- Crop water use depends on weather, crop stage and soil, not region alone.
- A water balance tracks rainfall, irrigation and crop use against allowable depletion.
- Use soil moisture sensors or checks to correct the estimate.
- Confirm local water rules before relying on any water source.
What determines how much water a crop needs?
Crop water use follows evapotranspiration: water lost from soil and through the leaves. Extension tools estimate it from a reference value based on temperature, sun, humidity and wind, adjusted by a factor for the crop and its growth stage. Water use is usually low in early growth, peaks around the time of full canopy and reproductive stages, and then drops.
Region shapes the weather inputs. Hot, dry, windy areas have higher demand than cool, humid ones, and rainfall patterns determine how much of that demand nature meets.
Growth stage is where many schedules go wrong. A young crop with a small canopy uses little water even in hot weather, while the same crop at full canopy can use much more on a similar day. Scheduling that ignores stage tends to over-water early and under-water later.
How does the water balance method work?
University of Minnesota Extension describes it as tracking water in the root zone like a bank account. Each day, add rainfall and irrigation, subtract crop water use, and keep a running deficit. When the deficit approaches the maximum allowable depletion, typically about half of the soil's available water in the root zone, it is time to irrigate.
Inputs include starting soil moisture, soil water holding capacity, rooting depth, weather-based ET and rainfall records. If your system has limited capacity, the source advises irrigating sooner and more often, which keeps the soil from falling behind.
Many extension offices and state agencies publish daily or weekly reference ET numbers for local stations, so ask which tool covers your area and how it should be adjusted for your crop and stage.
- Start with a measured soil moisture value
- Update daily with ET, rain and irrigation
- Irrigate as the deficit nears the allowable limit
What are the limits of the method?
It is an estimate. Runoff and deep drainage are hard to measure, errors in the starting soil moisture carry forward, and crop water use changes with weather and growth. The Minnesota source recommends combining the method with in-field soil moisture sensors, and notes that weather-based ET data may not be available for every location.
Check which local ET tools cover your area, and verify with a soil probe or the hand-feel method on a regular basis.
How do soil and rooting depth change the answer?
Sandy soils hold less water and need more frequent, lighter irrigation. Clay and loam soils hold more but can waterlog if overwatered. Shallow-rooted crops reach less of the profile and need closer attention than deep-rooted ones.
Dig and look. Checking root depth and soil moisture in several spots tells you more than a schedule on paper.
Drip, sprinkler and surface systems also differ in how evenly and efficiently they apply water, so the same crop can need different run times under each. Check system uniformity and ask extension how to evaluate it.
How do regions and crops compare in practice?
Western and arid regions often rely on irrigation for most crops, and earlier snowmelt in the western United States can mean water arrives before it is needed, as USDA Climate Hubs notes. Humid regions may use irrigation as insurance during dry spells, especially for vegetables and shallow-rooted crops. Vegetable and specialty crops often need more precise timing than commodity row crops.
Do not copy a neighbor's schedule across soil types or crops. Check your state extension irrigation guide for the range for your area.
What rules and cautions apply?
Water rights, well permits, district allocations and drought restrictions differ widely, so confirm your local water rules before planning any system. Irrigation also affects disease pressure and nutrient movement, so ask extension about timing and method for your crop.
Review irrigation records with an adviser each season. Good notes make the next year's schedule much better.
How do you keep irrigation records that help next year?
Log each irrigation event with the date, the field, the amount applied, the soil moisture reading before and after, and the crop stage. Add rainfall from your own gauge. This simple record shows whether you were running ahead of crop demand or behind it.
At the end of the season, compare the record with yield and quality notes for each field. Patterns usually appear quickly, such as one field that always runs dry first or a growth stage where stress reduced the crop.
Sources and further reading
Last reviewed: November 2026. Educational information, ranges only. Confirm timing with your county extension office.