Indiana, Michigan Corn at Peak Need for Water, Says Irrigation Specialist

    Irrigated corn in Indiana and Michigan has developed to where it is tasseling and will have its greatest need for water in the next three weeks, Purdue and Michigan State Extension irrigation specialist Lyndon Kelley says.

    During an average late July and/early August day, a 6-inch grass reference evapotranspiration, or rET, ranges from 0.17 to 0.23 inches of water use per day, or 1.4 inches per week, through evapotranspiration. Most irrigation scheduling programs have corn using 120 percent of the rET, which translates to a water use need as much as 2 inches per week depending on cloud cover and humidity.

    “Applying water when the crop needs it should be the producer’s most important mission,” Kelley said. “Applying water when the crop needs it should be the producer’s most important mission,” Kelley said.

    The week during tasseling, corn uses 120 percent of the rET, resulting in about 0.23 inch a day (1.6 inch per week) of water use. A cool, cloudy week would result in corn water use of 1.4 inch, and a hot dry week would result in 2 inches.

    Time of day not critical

    To make the best use of irrigation water, producers should try to provide 5-6 days’ worth of crop water use per application, typically 1 to 1.25 inches, Kelley said. These single, larger irrigation applications, rather than multiple, smaller applications, increase the amount of effective water available to the crop by reducing the water lost by evaporation in the corn canopy and on the residue and soil surface.

    The time of day irrigation water is applied has not been critical. “We have seen no major advantage or disadvantage irrigating crops either during the night or day,” Kelley said. “Avoiding afternoon irrigation, making multiple small applications and using pivot drop nozzles are all management practices developed for the arid west and have little to no advantage in irrigating Indiana and Michigan fields.”

    Kelley said many irrigation systems in Indiana and Michigan do not have the pumping capacity to keep up with the peak water use of the crop. That results in the crop drawing on its soil moisture reserves.

    Irrigation systems that can provide five gallons of water a minute per acre of irrigated land can provide 1 inch of water every four days or 0.25 inch per day if run continuously. Irrigation systems with less capacity to deliver water, or when crop water use is greater than 0.25” per day, have to rely on the soil moisture reserves to provide soil water or yield can be lost.

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    Myth of ‘cold shock’

    Irrigation applications made before the heat of the day can be beneficial to pollinating corn when afternoon temperatures are extremely high. By wetting the canopy and soil surface, temperatures are lowered and the relative humidity is raised, both of which can help pollination.

    “The myth of ‘cold shock’ to the crop scares some producers into avoiding irrigation just when it is needed the most,” Kelley said.

    For more information on irrigation water use and when to irrigate, see fact sheet No. 3 (“Irrigation Scheduling Tools”).

    Indiana producers can use data from their own evapotranspiration gauge station or rET data from Purdue Agricultural Centers weather stations to calculate the estimated corn water use per week.

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