Daily crop evapo-transpiration (ET) values are available on the World Wide Web at the following address:
Minnesota and Wisconsin (potential ETs only):
The map presents the daily ET estimates across the state via color contours. Information is updated seven days a week and continues through September. Each daily map remains stored on the web page and is accessible 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.
Each map displays a reasonable estimate of the potential daily ET value across the area based on the weather conditions of that day. The displayed daily ET value is very similar to the estimated daily crop ET from a full cover alfalfa crop of 6 to 10 inches in height.
For crops that have less than full canopy closure or that are nearing maturity, the daily potential ET value must be multiplied by a crop stage correction factor that ranges from 0.2 to over 1.0, dependent on the growth stage of the specific crop. Generally, once a plant’s canopy has nearly closed, the correction factor is equal to one. For some crops, however, this factor can increase to 1.10 to 1.15 during the crops’ critical growth period, as with corn between pollination and early dough stages.
The daily ET maps are created and managed by University of Wisconsin Extension Soils Scientist, Bill Bland. These potential ET daily contour maps are generated using data from local airport automatic temperature recording stations across the state and solar radiation estimates calculated from a GOES satellite. The satellite takes a picture about every ten minutes to estimate the daily solar radiation for a given location.
A comparison of the last two years’ actual ET values with ET estimates made using data from local weather stations at Staples has shown that the two values are similar, but actual values are about 10 percent greater than estimates reported by local ET hotline services from Staples.
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, Minnesota, by e-mail at jwright@tc.umn.edu or by phone at (320) 589-1711.
The University of Minnesota is an equal opportunity educator and employer.
This page is part of the Biosystems and Agricultural Engineering Department web at http://www.bae.umn.edu/