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Should You Keep the Corn and Soybean Seeds You Have?

Later planting means big decisions when it comes to the seed you use.

In machine sheds across the U.S., bags of unplanted corn and soybean seeds lay on pallets, taunting growers who cannot get in the field due to wet planting conditions. 

A month ago, the prevailing wisdom from university and seed company agronomists was to stick with the original, full-season selection of corn hybrids and soybean varieties to obtain maximum yield potential when the crop was planted. 

Now, the sentiment is that it may be time to switch to early-maturing seed products. 

After June 1, it’s Decision Time

June 1 seems to be the date that triggers a shift in corn hybrid maturity, switching crops altogether or taking prevented planting, according to Mark Licht, agronomist at Iowa State University. 

Planting at this late date will likely result in lost yield potential of 50 bushels per acre or more. Switching to soybeans has its considerations, too. If nitrogen and herbicide applications have been made, these are factors that have the potential to negatively affect soybean germination, emergence, and nodulation. Many herbicides do not allow planting soybeans the year of application. For delayed and preventative planting, the late coverage decreases each day from June 1 to June 25 in Iowa. In a prevented planting situation, crop insurance language states the “cause of loss must be insurable and common to the area,” Licht writes in an Iowa State University article

What happens when planting a full-season hybrid late? 

“The question is based, of course, on the perceived risk of the crop not reaching physiological maturity before a killing fall freeze and the yield losses that could result,” writes Purdue University agronomist Bob Nielsen in a report released last week by the university. “A related, and economic, concern with delayed planting of normal full-maturity hybrids is the risk of high grain moisture contents at harvest and the resulting costs incurred by artificial drying of the grain or price discounts by buyers.”

Ignacio Ciampitti, agronomist at Kansas State University, notes that corn emergence is way behind, which you expect in a year like this. In Iowa, for example, 76% of the state’s corn was planted (as of May 26), yet just 42% emerged. In Kansas, crop planting is 20% behind, but emergence is 30% behind. 

Yet, Ciampitti believes emergence is affected by waterlogged and cool soils. 

“Cold soil temperatures mean the pace of emergence is slow. Temperature is one of the main factors driving the growth of corn,” he says.

Therefore, that full-season “racehorse” hybrid may be even further behind at harvest. 

If you really, really want to keep the hybrid you already have on hand, there is still a glimmer of hope that it will mature before winter sets in, according to Purdue’s Nielsen, who notes that hybrids mature in fewer GDDs than predicted when planted late. Based on Purdue research from 2002, hybrids planted later than about May 1 mature approximately 6.8 fewer GDDs for every day of delay beyond May 1, through at least the second week of June, which were the latest planting dates evaluated in the research. For example, a hybrid rated at 2700 GDDs from planting to physiological maturity (black layer) and planted on May 31 reaches physiological maturity in less than 2500 GDDs after planting (e.g., 2700 - (30 days x 6.8)).

Licht said farmers need to use their best judgement and the judgement of their advisors to determine the best course of action. “Bottom line, if planting is delayed past June 1, make a realistic determination of remaining corn yield potential, possible soybean yield potential, and feasibility of delayed and preventative planting. Talk with crop advisers, Extension field agronomists, and insurance providers to gather information to make the best decision given the situation.”

Stick With Soybean Varieties For Now

In the May 26 Crop Progress Report, USDA projects soybean planting is only 29% in the nation’s 18 key soybean-producing states. That’s a whopping 37% below the five-year average for soybean progress. There’s no question that soybean farmers also feel under the gun to get the crop planted. 

How much yield are we losing by late planting? Since 1988, the University of Minnesota has conducted late-planting yield trials in many locations. Their research suggests that for each day planting is delayed beyond June 1, soybean yield potential decreases by 1%. It is less than that the first half of the month, and more the last half of the month, but on average, expect to lose about 0.4 bushels per acre each day planting is delayed. 

Weather conditions after planting pay a big role in how the crop fares, however. 

“Last year reaffirmed that we can have good yield with delayed planting, but remember that 2018 came with record high early-season temperatures that pushed the crop along,” write agronomists Seth Naeve and David Licolai in a May 22 University of Minnesota Crop Newsletter. “Coupled with late first frosts, we dodged a bullet. Let’s hope for the same in 2019.”

It may be tempting to switch to early-maturing soybean varieties, but don’t do that yet, advises KSU’s Ciampitti.

“When you move into the third week of June, you might need to start changing maturities. But if you make a change, make a significant change, or don’t do it all,” he says. For instance, if you’re used to planting a 4.7 maturity soybean, make a move to 3.7 maturity. Otherwise, it’s typically not going to make much difference in yield.

What will make up for later planting? Bumping up seeding rate, says Shawn Conley, soybean specialist at the University of Wisconsin. 

Research from South Dakota, Iowa and Wisconsin in 2016 and 2017 suggests that 154,000 seeds per acre was the optimum planting rate for maximum yield, when soybean planting occurred on May 24 (IA); June 21 (SD) and May 31 (WI). The seeding rates in the study increased 20K seeds per acre incrementally, from 60,000 to 160,000 seeds. Conley admits that its possible increasing rates greater than 160,000 seeds per acre could result in even higher yields, but “…given the flat response curve we find it difficult to believe we would have seen a significant yield response above where we are,” he writes in a May 20 blog post

Bottom line: if soybean seeding rate is low (110,000 seeds per acre or so), bump it up 20%. If seeding rates are more like 140,000 seeds per acre, bump it up 10%. 

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