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Pop quiz time! True or false?

Gil Gullickson Updated: 05/12/2015 @ 11:34am Crops Technology Editor for Successful Farming magazine/Agriculture.com

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.” 

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