Soggy impacts on corn, soil

GENESEO, Ill. — Heavy rains that have hit portions of Illinois and Indiana raise concerns over the survivability of corn that’s already planted and other issues that go along with a wet spring.

Wyffels Hybrids agronomy managers Eric Wilson and Ryan Gentle addressed many of the questions they are receiving from farmers during a recent “Keeping It Independent” podcast.

The length of time corn can survive in standing water depends on various conditions.

“We’ve had a lot of heat units, which is a good thing to get the corn out of the ground, but it’s actually a bad thing when we start to talk about saturated soil,” Gentle said.

“Basically, the warmer the soil temperature and the more growing degree units we get in a day, the faster the oxygen in the soil gets depleted. Generally, we say two to four days. Four days if we’re on the cooler side — 60 degree or less soil temperatures.

“The soil temperature has been higher than that. So, that makes me think that the corn still in standing water that was trying to come up or was just poking through probably in a lot of cases isn’t going to make it.

“If you know you have some spots out there and you’re going to have four or five acres of ponds to replant, let your DSM, your sales rep know so they have some corn for you set back for that.”

“Unfortunately, the most sensitive time for flooding for a corn plant is about this stage. The growing point is below ground. They’re trying to develop roots. It takes a lot of oxygen to do that,” Wilson added.

“You get bright, sunny days where we have good GDUs, good heat, I would definitely expect survival to be on that shorter side of the two- to four-day window. If you have three acres of wet holes that you’re going to need to replant, get a hold of somebody so they can get that seed lined up and get things moving a long.

“It sounds like we’re going to avoid a lot of whole field replant situations. That’s not to say there won’t be some somewhere.”

Replant Decision Tool

Wilson acknowledged that he enjoys the science behind replant decisions in his role as an agronomist.

“There’s a lot of really good research that has gone into planting date, stand establishment, and it’s one of those things, even though I know can be a very emotional thing when you’re looking at a field that looks tough, but it does truly kind of come down to numbers,” Wilson said.

“Based on the research we’ve done in the past, it kind of comes down to what do we have now, when was it planted and when we can get back in there to make an expected replant to make that decision.

“So, this is me speaking not as a farmer looking at someone else’s field. Sometimes, it’s an easier decision to make.”

To help growers make replant decisions, Wyffels has developed a web-base replant calculator.

“The Wyffels replant calculator really works well. It spits out a green return-on-investment, dollar-per-acre figure after you work through it or a red ROI if you’re going to lose money by replanting,” Gentle said.

“In general, if you sum it up for this time of year, we still have some time for 100% potential on corn yield if you would need to tear up and replant if you can get it in the first half of May.

“If you’re putting your replant day in for May 25 to June 1, if it’s a 27,000, 28,000 stand it tells you to leave it because if you’re getting to June 1 you might only be at 85% of full yield potential with a replant.

“I tell guys that just because they replant doesn’t mean you’re guaranteed 35,000 on that replant stand. We can get a rain or another event comes along and you’re still at 28,000 and all of sudden you’re at June 5. It’s an emotional decision.”

“The way we’ve designed that calculator, you can put in your own numbers. You can put in the price of corn. You can put in your own number of what it’s going to cost you to terminate that stand. It is very customizable. It’s a very useful tool because you can customize it to your operation,” Wilson added.

Diseases

Saturated soils can also be ripe for diseases such as seedling blights.

Rya Gentle said the warmer soils will help keep seedling blights in check. Seedling blights favor cold, wet conditions.

In addition, quality seed treatments with several modes of action will also help fight off blights.

“For crown rot, it’s really to early to tell. Every field in the Midwest has fusarium in it. That’s just the way it is, and a lot of times our seedlings get infected with crown rot. With a V4, V5 plant you can split that open all the way through the growing point and find some crown rot there, but it really depends on how the rest of the growing season goes,” Gentle said.

“Do we have adequate moisture, do we have adequate fertilizer out there or do we stay relatively disease free and that corn is happy and healthy and grows right through that so the crown rot never has a chance to take off.

“Yes we’re wet, but we were really wet last year in the April planting time frame and we were really cold, and everybody was predicting crown rot was going to be terrible. It was a non-issue because we had a great rest of the growing season.”

“Crown rot tends to be very opportunistic. I tend to see it more when we have a hot, dry later growing season or grain-fill period, especially following a cool, wet spring or cool, wet planting conditions. I tend to see it more when it turns hot and dry when those plants are already stressed to the max and then crown rot seems to get a good foothold and make things worse in a lot of those cases,” Wilson added.

Nitrogen Loss

Another issue that comes to the forefront from heavy rains and ponding in fields is nitrogen loss through leaching or denitrification, the volatilization of nitrate.

“If we have ponded field conditions, warm temperatures like we have, a lot of times I think we underestimate how much nitrogen we can denitrify in those situations. Granted, it might only be specific areas of the field, but a lot of times after that water goes down if we have plants that survived, you see that yellow tinge. That’s a pretty good indication that you’re probably a little short of nitrogen, and obviously pretty short on oxygen, as well with the saturated soil conditions,” Wilson said.

“I’ll mention a good rule of thumb. This is out of Iowa State University, but I’m sure it’s very applicable to Illinois, as well. If we get more than 15 inches or rainfall between March 1 and June 30, that would constitute the need for an additional nitrogen application. It’s not usually a lot, a lot of times it’s 40 to 50 units that’s very beneficial.

“But if we have wet springs with either leaching or denitrification, just a little bit of extra nitrogen can go a long way to make sure we maintain yields the best we can.

“We don’t necessarily have to wait until June 30 to make that decision. If we’re over the halfway point of rain and we’re encroaching on the 15-inch mark, a little bit of nitrogen can go a long way.”