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Irrigation management strategies

Deciding when to irrigate to optimize production is a daily judgment call that requires you to consider several factors. Many of these factors change as the crop develops.

Below are some general guidelines to consider when developing a water management plan and setting allowable soil water deficit limits.

Strategies by season and growth stage

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Increase allowable soil water deficit

Another possible irrigation water management plan is to set the allowable soil water deficit equal to, or slightly greater than, the irrigation system’s normal net application amount.

For example, if the typical application is .75 inches net, then choose a planning deficit limit of .75 to 1 inch. If this is greater than 50 percent of the available water capacity in the root zone, make the amount smaller – especially during the critical stages of crop growth – to reduce the risk of moisture stress.

This strategy will require more irrigation applications than the variable deficit strategy described earlier.

Consider crop water use

Crop water use is the amount of water given up to the atmosphere by a crop due to evaporation from the soil surface and transpiration through the plant leaves. Crop water use is also called evapotranspiration (ET).

Factors that influence ET

Daily crop water use changes throughout the growing season due to weather variation and crop development. The checkbook method needs daily ET estimations to update the soil water deficit balance.

Crop water use depends on many factors including:

  • Crop type.

  • Growth stage.

  • Climatic conditions; parameters that have a major effect on a crop's daily water use include maximum and minimum temperatures, solar radiation, humidity and wind.

  • Soil moisture.

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Consider pumping capacity

A system’s pumping capacity defines the ability of the irrigation system to refill the soil profile with water. Knowing this capacity enables you to better judge when to start an irrigation in order to complete an irrigation before any part of the field exceeds the allowable soil water deficit.

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Vasudha Sharma, Extension irrigation specialist and Jerry Wright, emeritus Extension engineer

Reviewed in 2019

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