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Daily Crop “ET” Info Available on the Internet
Daily Crop “ET” Info Available on the Internet
Jerry Wright, Minnesota Extension
Engineer
Minnesota and Wisconsin growers needing daily crop evapotranspiration
(ET) for irrigation scheduling can access the internet to obtain daily
ET potentials. The maps for Minnesota and Wisconsin potential crop ETs
are available at: http://www.soils.wisc.edu/wimnext/
The Minnesota and Wisconsin ET daily statewide color-coded maps are
available now and throughout the growing season. Each daily map gives
a reasonable estimation of the potential (reference) ET across the region
based on the real weather conditions for that day. Potential ET values
are very similar to the actual daily crop ET of a full canopy crop.
Users can request that the daily values for a given field site be sent
directly to them by e-mail each day.
These reference ET daily contour maps are generated using data taken
from numerous local airports automatic temperature recording stations
across the state and solar radiation estimations, calculated from a
GOES satellite that takes a picture about every 10 minutes. A comparison
of values from the past few years with ET estimations from local weather
stations at Staples and Morris, Minnesota, has found them to be very
similar but with the web site values generally being around 10 percent
greater in value.
The daily Wisconsin-Minnesota ET maps are created and managed by Bill
Bland, University of Wisconsin Extension Soil Scientist. The daily ET
value from the map must be multiplied by a crop coefficient (Kco) constant
that may range from .25 to 1.0 and depends 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 holds there until produce starts to mature. As a crop matures,
the actual ET of some crop types decreases slightly each day as they
come to maturity, hence the crop correction factor will go from 1.0
to as low as .40.
Keeping track of the crop’s daily ET use, along with regular in-field
soil moisture checks, can go a long ways toward helping you to optimize
the crop’s growth while reducing the potential for leaching of
inputs like nitrogen into the groundwater.
These daily ET values best serve the user if recorded on a calendar
log like an irrigation checkbook worksheet or computer spreadsheet for
quick reference when making irrigation decisions. Consider assigning
the updating task to one of the younger members of your family. Worksheets
from the University of Minnesota Extension Service bulletin #1322, Irrigation
Scheduling: Checkbook Method, can be printed off the web at http://www.extension.umn.edu/distribution/cropsystems/DC1322.html
or may be purchased with a credit card by calling 800-876-8636 or 612-624-4900.
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 you can contact your local Extension or SWCD office.
