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Minnesota irrigators and crop consultants needing daily crop evapotranspiration (ET) information for irrigation scheduling can access this information on the Internet. Color contoured state maps show daily ET potential, according to Jerry Wright, engineer with the University of Minnesota Extension Service.

Maps for Minnesota and Wisconsin are on the web at http://www.soils.wisc.edu/wimnext/water.html. Maps for North Dakota and the Red River Valley are at http://www.ext.nodak.edu/weather/cropwater/. The maps for Minnesota and Wisconsin show potential, or reference, ETs only, while those for the Red River Valley show estimated daily ETs for several crops.

The Minnesota and Wisconsin daily ET maps are available between mid-April and the end of September. The ET values are based on the weather conditions for the day. Daily ET values can also be sent to users directly by e-mail upon request.

"Potential ET is very similar to the daily crop water use (ET) from an alfalfa crop 6-10 inches tall or a closed-canopy corn field," says Wright. For crops with less than full canopy a crop correction factor needs to be applied to estimate the actual ET.

"Keeping track of a crop's daily ET use, along with regular in-field soil moisture checks, can go a long way toward helping you optimize a crop's growth," says Wright.

"Doing these things will also reduce the potential for leaching of inputs such as nitrogen into the groundwater."

Wright recommends keeping a calendar log such as an irrigation checkbook worksheet or computer spreadsheet for quick reference when making irrigation decisions. He suggests assigning the updating task to a younger family member.

For more information on how to use daily crop ET information, contact Wright at (320) 589-1711 or jwright@umn.edu, or contact your county office of the U of M Extension Service or Soil and Water Conservation District.