Irrigation Management – Temperature Relief

James Adkins, Agricultural Engineer; adkins@udel.edu

Both corn and full season soybeans are predicted to use around 0.23” per day next week. Hopefully, Tuesdays storms will enable farmers to reset their soil water balance. Keep in mind that a typical corn or soybean crop will need irrigation starting Friday/Saturday or before even if Tuesdays rain refills the profile.

The information presented below is an example of the soil moisture status at University of Delaware’s Warrington Irrigation Research Farm. Actual field values will vary greatly depending on crop stage, soil type and local rainfall. There are many tools available that provide field by field values to assist farmers in making irrigation scheduling decisions including paid services through local crop consultants, irrigation equipment manufacturer’s, Climate Corp, etc and free tools like KanSched and the Delaware Irrigation Management System (DIMS) http://dims.deos.udel.edu/

Field Corn
Daily corn evapotranspiration (ET) rates for April 25th planted 114 day corn at R2 averaged 0.26”/day for the past week. While the temperature has been very high with plenty of sunlight, the high humidity has kept crop ET rates under the 0.3”/day we sometimes see at this stage. Soil moisture sensors in the field are in line with the model predictions and have been a good confirmation that our estimated soil moisture values are correct. This field received 1.14” of rain on July 17 in addition to 1.5” of irrigation in 5 events since last Tuesday. This same field is predicted to use 0.14”, 0.20”, 0.25”, 0.27”, 0.28” for Tuesday 7-23 – Monday 7/27 for an estimated daily usage of 0.23” per day for the upcoming week. These are estimated values and are no substitute for daily ET use models and field level soil moisture data.

At this point in the growing season most corn fields are at least into the VT – R2 stage; Crop water usage will be nearly the same from V14 until R2/blister stage. Farmers should continue to intensively irrigate through the R2 stage and gradually taper off through R3 until black layer.

Irrigated Corn Soil Moisture Report for the UD Warrington Farm Stage R2 – DIMS Report

Full Season Soybeans
May 2nd planted soybeans at the UD Warrington Irrigation Research Farm are into the R3 stage as of July 11th. We received 1.14” of rain on 7/17 and applied a total of 1.2” in 4 irrigation events over the past week. The average daily crop water use was 0.22” per day and the predicted daily ET for next week is 0.26” per day (the same amount as corn). We have observed high rate of water use from the shallow profile; Remember to irrigate in small but frequent doses to avoid pushing water beyond the root zone. Multiple years of soil moisture sensor data show soybeans to use water primarily from the shallow (0-8”) soil profile.

Double Crop/Late Season Soybeans
Continue to irrigate in small amounts of around 0.2-0.3 inches to maximize canopy development. Keep in mind that irrigation that infiltrates beyond 6” will be of little benefit to the crop. Barley and early wheat beans should be using an estimated 0.2” per day.

Irrigated Soybean Soil Moisture Report for the UD Warrington Farm Stage R3 – DIMS Report

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