Irrigation Management: Rain for Sussex, Scattered Showers for Others

James Adkins, Agricultural Engineer;

Tuesday afternoon brought rain to most of Sussex County while spotty showers provided relief to some northern areas on Wednesday. Those who received profile filling rains (100% of available water) will have 5-6 days before irrigation will be needed for corn and 4-5 days for soybean. Full season corn is nearing black layer and the daily water usage is starting to fall from the 0.25+”/day peak into a more manageable 0.13”/day average. Full season soybeans are still using considerable water but not nearly as heavily as past weeks. Soybean water use will continue until the leaves start to yellow.

24 Hour Rainfall Totals for Tuesday 8/13

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)

Field Corn
Daily corn evapotranspiration (ET) rates for April 25th planted 114 day corn at R4 averaged 0.13”/day for the past week. This field received 1.48” of rain in 2 events on Tuesday and Wednesday and 0.6” of irrigation on Sunday. This field is predicted to use 0.12”, 0.14”, 0.16”, 016”, 0.14” for Friday 8-16 – Tuesday 8-20 for an estimated daily usage of 0.14” 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 R4 stage. UD research on when irrigation can be stopped has been largely inconclusive. Farmers should continue to irrigate until black layer. We have no data to suggest that irrigation after black layer has yield or test weight benefits.

Irrigated Corn Soil Moisture Report for the UD Warrington Farm Stage R4+ – DIMS Report

Full Season Soybeans
May 2nd planted soybeans at the UD Warrington Irrigation Research Farm are into the R5 stage as of Aug 16th. The average daily crop water use for the past week was 0.16” per day and the predicted daily ET for next week is 0.20” per day. Despite the profile filling rain event(s) on Tuesday and Wednesday, this field will require irrigation on Sunday. 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 so use water primarily from the shallow (0-8”) soil profile.

Double Crop/Late Season Soybeans
At this point double crop soybeans have full canopied. Once full canopy is achieved, late soybeans will use the same amount of water as the full season beans above.

Irrigated Soybean Soil Moisture Report for the UD Warrington Farm Stage R5 – DIMS Report