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Pop quiz time! True or false?

There are lots of old wives’ tales about growing corn. The thing is, though, some of these beliefs might actually be true. Five are put to the test with agronomists and soil scientists in this quiz. Take it to see how you stack up against the old wives – or maybe that know-it-all brother-in-law or neighbor!

1. Transgenic traits increase yields.

False. If insects are present at economically damaging levels, the traited hybrid will outyield the same hybrid without the trait. In a yield comparison with no insect pressure, though, both hybrids would yield the same. 

“Transgenes protect yield but don’t increase it,” says Roger Elmore, Iowa State University (ISU) Extension agronomist. 

There’s a catch, though. The yield edge that a traited hybrid enjoys in the presence of insect pressure assumes no yield drag when the transgene is inserted. Yield drag did occur for several years when Roundup Ready soybeans debuted in 1996. 

2. Snow-Covered corn will yield poorly. 

False. This was exactly what happened across the many Midwestern areas in 2013, when early May snow covered early planted corn.

“We thought there might be imbibitional chilling when corn absorbed cold water,” says Elmore.

Emergence, though, was similar between corn planted before the snowfall and that planted on May 15 in ISU corn trials. 

“The corn planted on April 30 emerged on May 17,” says Elmore. “The corn planted on May 15 emerged on May 22.”

The corn planted on May 15 yielded slightly more: 208 bushels per acre vs. 200 bushels per acre for the corn planted on April 30. It’s important to note, though, that yields did not crash due to the early May snowfall. 

3. Corn-after-corn yields are similar to corn following soybeans.  

False. At least that’s what a 2011-2012 ISU trial shows, which was compiled by John Sawyer and Dan Barker, ISU soil specialists. The trial pegged a 13.2% yield penalty for corn following corn compared to corn following soybeans. However, yield penalties may be less in high-yield environments, notes Elmore.  

4. Narrow rows always increase corn yields.

False. OK, we might as well come clean. A sentence in a true-or-false quiz that uses always is always false! 

Seriously, yield responses hinge on the initial corn-row width. ISU research from 1998 to 2000 shows narrowing rows from 38 to 30 inches boosted yields by an average 2.9%. 

However, narrowing row spacings from 30 to 15 inches boosted yields by just .3% in ISU studies from 1995 to 2000. 

Row-width response hinges on the degree of light interception. 

“If you get 95% light interception at silking in 30-inch rows, you are maximizing yield,” says Elmore. “Going to 20-inch rows will not help.” 

One factor that has helped 30-inch rows maximize light interception is a breeding emphasis on upright leaves and thicker planting. 

“These help us capture more light at silking than my dad and grandpa could have done,” says Elmore. “It is a combination of genetics and management.” 

In northern areas, narrow rows show a bigger yield advantage. University of Minnesota (U of M) tests show corn in 22-inch rows yielded 4% to 5% more than corn in 30-inch rows in northwestern Minnesota. Very little yield advantage was found in rows narrower than 30 inches in southern and central Minnesota. Results vary, but the greatest benefit to a narrow-row planter is likely the potential for higher soybean yields, says Jeff Coulter, U of M Extension agronomist. 

Here’s something to consider, though. “For decades, we have focused on breeding hybrids that perform best in 30-inch rows,” says Elmore. “So in 30-inch rows, we have had selection pressure.” 

Some seed companies are researching planting corn in 12-inch rows and have several hybrids that do well in this spacing at 50,000 to 60,000 plants per acre.

Elmore points out that if more hybrids like these are developed under narrow rows, more yield advantage may occur.

“Stay tuned,” he says. 

5. Volatile weather is real. 

True. Most climate scientists agree that weather is becoming more extreme and volatile.

“In the past 50 years, there has been an increase in the percentage of heavy precipitation events,” says Elmore.

Increases in spring precipitation at Ames, Iowa, have decreased the number of workable field days in April through mid-May by three and a half days from 1995 to 2010, compared to the 1979-to-1994 time frame.

“The stress that puts on producers with fewer workable days is tremendous,” says Jerry Hatfield, director of the USDA-ARS National Laboratory for Agriculture and the Environment at Ames.

Rainstorms also are becoming more intense. A measurement of Des Moines, Iowa, precipitation shows that from 1900 to 1960, only two years had more than eight days with rainfall amounts tallying 1.25 inches or more, says Hatfield. 

From 1960 up until now, there have been seven years with more than eight days tallying 1.25 inches of precipitation and above.  

On the plus side, more volatile weather has lengthened the growing season. 

“We plant earlier than ever before, plant longer-season hybrids, and harvest later,” says Elmore. 

This also means you should anticipate more variability like the 2012 drought and 2013’s prolific spring precipitation, Elmore points out.

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