Daily Crop “ET” Available on the Internet

Jerry Wright, Extension Engineer at the West Central Research and Outreach Center at Morris, MN

Producers and crop consultants in Minnesota and Wisconsin that need daily crop ET information for irrigation scheduling can access the internet at the following address to obtain the past day’s daily ET potential estimates:
Minnesota & Wisconsin (potential ETs only): http://bob.soils.wisc.edu/wimnext/water.html

The map presents the daily ET estimations across the state via color contours placed over the map of the two states. Information is updated 7-days a week and continues through September. Each daily map remains stored on the internet page and is access able any time. The daily values for a given field site within the map area can also be sent directly to a user by e-mail each day if requested over the WEB site.

Each daily map gives a reasonable estimation of the potential (reference) ET value across the area based on the weather conditions of that day. The daily potential ET value is very similar to the daily crop ET from a full cover alfalfa crop of 6 to 10 inches in height.

These potential ET daily contour maps are generated using data from local airport automatic temperature recording stations across the state and solar radiation estimations calculated from a GOES satellite that takes a picture about every 10 minutes to estimate the daily solar radiation for a given location. A comparison of the last two years values with ET estimations from local weather stations at Staples and Morris has found them to be similar but about 10 percent greater in value than reported by local ET hotline services.

The daily ET maps are created and managed by University of Wisconsin Extension Soils Scientist, Bill Bland. This daily ET value must be taken times a crop coefficient (Kco) constant that is dependent on the growth stage of the specific crop. Generally, once a plant’s canopy has nearly closed the Kco is equal to one. For some crops however this Kco may become slightly larger to around 1.1 during a crops’ critical growth like with corn between late pollination and early dough stages.

Keeping track of the crop’s daily ET use and regular in-field soil moisture checking can go a long ways in helping an operator optimize the crop’s growth while reducing the potential for leaching of some crop inputs like nitro gen 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. For more information on how to use daily crop ET information contact Jerry Wright, Extension Engineer at the West Central Research and Outreach Center at Morris, MN by e-mail at jwright@tc.umn.eduor by phone at 320-589-1711.

Co-Editors:Bill Hutchison, Department of Entomology, University of Minnesota, hutch002@tc.umn.edu
Jeanne Ciborowski, IPM Program, Minnesota Department of Agriculture, jeanne.ciborowski@state.mn.us
Cindy Tong, Department of Horticulture, University of Minnesota, ctong@extension.umn.edu
Production Editor: Suzanne Wold, Research Specialist, University of Minnesota, woldx018@tc.umn.edu

Disclaimer
Reference to products in this publication is not intended to be an endorsement to the exclusion of others which may have similar uses. Any person using products listed in this publication assumes full responsibility for their use in accordance with current directions of the manufacturer

Last Revised May 18, 2000.
The University, including the Minnesota Extension Service, is an equal opportunity educator and employer.©1999 Minnesota Extension Service, University of Minnesota. All rights reserved. Contact copyright@extension.umn.edu for information on reproduction or use of this material.