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DFP-Brad-Robb-Trent-Irby.jpg Brad Robb
Dr. Trent Irby updated attendees at the Mississippi Agricultural Council Meeting in Orange Beach, Ala., about the challenges Mississippi soybean producers may face as this year’s crop moves toward harvest.

Mid-South soybean growers face challenges after wet planting season

Mid-South soybean growers face replant, irrigation, and harvest challenges, as well as a strong possibility of reduced yields.

An historic wet planting season left Mid-South soybean growers facing replant, irrigation, and harvest challenges, as well as a strong possibility of reduced yields. “This has been a planting season that just will not end,” says Trent Irby, associate Extension professor, Mississippi State University, speaking at this year’s Mississippi Agricultural Industry Council meeting in Orange Beach, Ala.

“We’ve stayed two to three weeks behind the entire year because of rain, excessive flooding, and so many replanted acres. That likely hurt our overall yield potential, I’m afraid.”

Some fields planted in a timely fashion were pounded with rain which caused thin stands. In some cases, lower halves of fields were flooded out, necessitating replanting which led to difficult management considerations.

Irby used 2018 data to advise growers on specific plant populations to shoot for when replanting. “Our past research has simulated thin stands which were initially planted toward the end of April to May 1,” says Irby. “We would remove percentages of plants from our plots and create different replant scenarios by spot planting back into them. This year we implemented a planting date component to see how the crop would respond to low populations and plant back scenarios to different planting dates.”

If an entire field was lost after first plant, Irby reported growers may see a significant reduction in yield on the replant. “Planting date is critical in terms of yield potential,” says Irby. “In our research to determine if we should keep certain low populations rather than completely starting over, we seeded at 130,000 seeds per acre, and in the case of 50 percent stand loss, which resulted in just shy of 60,000 live plants per-acre, we saw as much as a 10 percent yield reduction.”

At this population, says Irby, the question then becomes: Do we replant? “In the case of populations above 60,000 plants per acre, spot planting into the existing stand did not improve the yield potential, and we saw a yield reduction when having to terminate the poor stand and start over,” says Irby. “But below 60,000 plants per-acre, we saw improvement when spot planting to increase the overall population, which was still better than terminating and completely starting over.”

That was not always possible this year with all of the partial and completely flooded fields. “Many fields had to be completely terminated and replanted to allow growers to properly manage them for things like weed control and irrigation,” says Irby. “Sometimes, we have to terminate whole fields and start over, but in these cases, we know the yield potential will decline simply because of having a later planting date.”

Irrigation, genetics, harvest aids

Despite the inordinate amount of rain in the Mid-South this year, Irby has still received irrigation questions about scheduling on top of soil moisture sensors. “If a grower keeps an irrigation threshold of 125 centibars, that is where we have seen drought stress creep in and the possibility of yield reduction increasing,” says Irby. “Somewhere in that 80 to 90 centibar range is where I like to see an irrigation threshold.”

Irby referred to some past irrigation research from Dr. Jason Krutz that evaluated different recommended holding irrigation thresholds to the soybean crop’s growth stages. “They evaluated 50, 85 and 125 centibar thresholds up to R2, and then had another set of plots where the same trigger was used up to R3/R4 and then R5/R6,” says Irby. “The only place they saw a yield reduction was when water stress was allowed in the seed fill part of the window. Maintaining proper irrigation, especially if the crop is moving into the R5 stage, is important to avoid losing yield.”

A comprehensive Mid-South research project several years ago examined maturity Groups 3, 4, 5 and 6, by planting dates of mid- to late April, for an early planting date, a mid-planting date in May, with the late planting date being in June. “I was getting questions in May about maturity groups and this research has shown Group 4s hold an advantage all the way through May — in terms of yield potential,” says Irby.

“We have some excellent genetics, and growers need to choose them and go with the earlier-maturing varieties whenever possible. Individual maturity groups no longer hold a yield advantage when planting moves into June or later. However, staying with these earlier-maturing varieties still hold an advantage, as they will finish earlier in the fall, allowing growers to get them out of the field and avoid late-season rains and possible quality damage.”

Harvest aids may play a more prominent role in this year’s soybean harvest, especially with so many spotty stands and such variability across the region caused by delayed planting and emergence. “I suspect we’ll see a lot of physiological maturity variability when this year’s crop starts turning,” says Irby.

“It’s possible we could see some green stem issues, but it will probably be on a case-by-case basis. Because we’re still in a down soybean market, unneeded inputs can hurt a grower’s bottom line. If it will help get the crop out efficiently, a good harvest aid application might help smooth out the unevenness in the crop’s maturity.”

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