As many of you know, Dr. Angela McClure, our Extension Corn and Soybean Specialist, retired at the end of June after 20 years of service.  Dr. McClure will be greatly missed.  We are actively searching for a replacement and hope to have the position filled quickly.  In the meantime, my colleagues and I will do our best to cover these commodities until the position is filled.

Rainfall (or lack thereof) has been the main topic of conversation in double crop soybean, full season soybean and corn.  Several specific questions have arisen lately on irrigation management and how to maximize returns during 2022.  With help from several of my colleagues, I’ve worked to update a previous post of Dr. McClure’s with information from 2022.

Corn Years ago when I worked in the MS Delta, I was told the best tool for irrigating corn was a goldfish placed near the furrow pipe-“just keep the goldfish alive and you’ll have done a pretty good job”.  This is an extreme example, but it does capture the point; when mother nature fails to provide rainfall, most of our irrigation systems will struggle to keep up during peak corn water use.

Use by growth stage Late corn isn’t very hard to find in Tennessee, but the average field is between VT and R3; right in the peak of water use.  From V13 to silking, the effect of drought stress becomes more severe. Yield loss due to drought stress is greatest at silking, followed by blister. The majority of our irrigation systems will have to run 24/7 in order to meet crop water use during our current growth stages and if we fall behind it will be very difficult to catch back up.  Water use remains very high until we move past the dough stage.  You can read more on corn irrigation in Dr. Shekoofa’s article from last month.

Timing of Events While we typically try to not irrigate cotton in the morning, corn is different; corn will wait to release pollen until the tassel has dried and silks are capable of retaining pollen even through irrigation events.  Furthermore, most plants will release pollen between 9AM-11AM and again in the late afternoon. As a result, overhead water can be applied even during pollination with little to no impact on pollination.

Termination In a normal year, it is usually recommended to irrigate until ears reach the ¾ milk line (about 50 days from silking date).  2022 is not a normal year.  Unless we capture multiple, large rainfall events in the immediate future, we will likely need to continue to irrigate until black layer (about 65 days from silking date).

Soybean Irrigating soybean is more like irrigating cotton than irrigating corn; while irrigated beans are almost always better than dryland beans, over-irrigation of soybean can significantly decrease yields through lodging and increased disease pressure.

Use by growth stage A checkbook method based on estimated crop water use is a requirement to hit the sweet spot- put on enough water without overapplying.  While in-field measurements of crop water use can be helpful every year in estimating plant water use and preventing overapplications, they are particularly valuable this year.   Normally, beans do not need irrigation water during vegetative stages.  During 2022, irrigation during vegetative stages may be warranted to make sure adequate water is available during R3.  You can read more about soybean irrigation here and you can read more about in-season measurements here.

Timing of Events Irrigating late in the afternoon can increase the humidity level of the canopy throughout the night and create a favorable environment for diseases.  Beginning irrigations during the early morning and stopping late afternoon will allow the canopy time to dry.  However, irrigations should continue through the evenings and into the night if demand cannot be met during the morning to afternoon hours; eliminating drought stress should take precedence over creating a favorable environment for diseases during peak water demand.

Irrigation Termination Irrigation should be terminated by R6 to R6.5 or full seed stage (more than 50% of plants have touching seed in at least one of the top 4 nodes).  Dr. McClure’s research across three years at Milan suggests adding water beyond R6.5 will likely reduce yields.

Special thanks to Dr. Trent Irby, Soybean Specialist at Mississippi State University for assisting with some of the content in this article.  Don’t hesitate to reach out to your local county office if you have any questions on this content or on anything else pertaining to corn and soybean over the next few months.