Daily crop evapotranspiration (ET) information can be used by Minnesota irrigators to help plan irrigation scheduling. This information is currently available for the 2006 season and can be easily obtained from the internet by going to one of the web pages listed below, or by contacting one of the following local ET service providers:

The Minnesota and Wisconsin ET web page presents daily colored coded maps, like the map to the right, each day of the week; and it displays a reasonable estimation of the potential ET value across the state based on the actual weather conditions of that day. Potential ET values are very similar to the daily crop ET for a full canopy crop.

The daily values from the web site can also be sent directly to a user by e-mail each day for a given field site within the map area if requested over the web site.

To estimate the daily ET value for a crop before full canopy or near maturity the ET value must be taken times a crop coefficient (Kco) constant that may range from .25 to 1.0 and is dependent on the growth stage of the specific crop. Generally, for annual crops, the correction factor starts out around .25 and increases to 1.0 or greater as the plant nears full canopy and this value holds there until the plant starts to mature. As a crop matures, some crop types will have their actual ET decrease slightly each day as they come to maturity, hence the crop correction factor will go from 1.0 to maybe as low as .40 as the leaves senesce and reach maturity. Crop coefficients for specific crops can be obtained from Jerry Wright, Extension Engineer at jwright@umn.edu.

Keeping track of the crop's daily ET use and regular in-field soil moisture checking can go a long way toward helping an operator optimize the crop's growth while reducing the potential for leaching of some crop inputs like nitrogen into the groundwater.

These daily ET values best serve the user if recorded down on a calendar log like an irrigation checkbook worksheet or computer spreadsheet for quick reference when making your irrigation decisions. Consider assigning the updating task to one of the younger members of your family.

Irrigation checkbook spreadsheets can be found on University of Minnesota Extension website at:
www.extension.umn.edu/distribution/cropsystems/DC1322.html;
or one can purchase a computerized spreadsheet version of the Checkbook for $35 from the WCROC office at Morris. An alternative version of a checkbook spreadsheet can be also downloaded from the Wisconsin ET web site.

For more information on how to use daily crop ET information contact Jerry Wright, Extension Engineer at the West Central Research and Outreach Center in Morris, MN (320) 589 -1711 or jwright@umn.edu or your local Extension or SWCD office.

printer-friendly PDF version