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Take a stand on corn populations

How many corn seeds should you plant?

That question is now more complicated, and the drought of 2012 didn’t help. If you knew it was going to be bone dry this year, you could plant accordingly. Don’t forget that even during drought, some fields yielded exceptionally well and needed every plant out there.

Jeff Coulter, University of Minnesota (U of M) Extension agronomist, has examined several corn-yield trials from recent years, and he offers these eight take-home points for 2013.

1. Know yield goals.

As yield goals rise, you need more plants. Estimates from South Dakota and Illinois trials show final corn plant population needs to rise 740 to 940 plants per acre for every 10-bushel yield goal increase. If your yield goal moves from 180 bushels an acre to 200, you need to plant an extra 1,500 to 2,000 plants per acre.

2. Hold back seed with high-yield goals.

High yields over 200 bushels per acre do not require high seeding rates. Typically, though, at least 32,000 plants per acre are needed for such yield levels in southern Minnesota and similar environments, Coulter points out.

In trials across southern Minnesota last year, Coulter and colleagues researched how seeding rates affect optimal nitrogen (N) rates. They evaluated seeding rates of 30,000, 36,000, and 42,000 plants per acre. The two upper rates maximized yields, says Coulter, at just over 220 bushels per acre. (Minnesota was not as impacted by drought as other states.)

The 30,000-plants-per-acre rate yielded significantly lower at all three locations. The yield difference at the higher levels also maximized the economic returns with seed priced at $225 a bag, a corn selling price of $7.25 a bushel, and N at 50¢ per pound.

3. Don’t always apply more N.

There’s a theory that heavier stands require more nitrogen to produce big yields. Minnesota researchers used four nitrogen rates – 65, 110, 155, and 200 pounds per acre – on all three populations. The 155-pound rate maximized yield and maxed economic performance, too. Even at 36,000 and 42,000 plants per acre, Coulter says there was no advantage to increasing N beyond 155 pounds.

4. Expect yield penalty for late-planted corn.

Coulter says producers have wondered if higher populations might remove the yield penalty for late corn planting. Research examined late-April, mid-May, and late-May planting dates. The late-May plantings yielded about 25 bushels per acre less than late-April at all populations, from 16,000 to 44,000 plants per acre. There’s not much you can do to compensate for delayed planting, he says.

5. Don’t plant more seed.

In most of the Corn Belt, narrow rows do not require higher stands. One theory states that corn plants benefit more from the extra breathing space offered by narrow rows. Minnesota studies from two years ago comparing 30-inch corn rows to 20-inch rows found yields maxed out at about 34,000 plants per acre for both row widths. Yields stayed close all the way to 44,000 plants per acre.

“It’s just pretty hard to beat 30-inch rows in southern Minnesota,” he says.

That may change in places like northwest Minnesota, he says. There, many growers plant corn in 22-inch rows, and research is more favorable to higher populations in narrow rows.

“The 22-inch rows have yielded 4% to 5% more at the upper populations,” says Coulter. “In this region, the optimal seeding rate is about 3,500 plants per acre higher in 22-inch rows, and in on-farm trials conducted from 2009 to 2011, both yields and economics were optimized at over 40,000 plants per acre in 22-inch rows. Many of those fields in northwest Minnesota are planted at about 34,000 plants per acre. Many growers there could get an economic edge if they pushed above 37,000 and in some fields went up near 40,000,” he says.

6. Take advantage of twin rows.

If twin rows have an advantage, it may be at higher corn stands. This subject involves planting two rows close together (8 inches apart) on 30-inch centers. Theoretically, the twin-row pattern results in more equidistant plant spacing, which encourages better growth and ultimately more yield.

In several years of on-farm tests, U of M agronomists compared regular 30-inch rows to twin rows at 33,000, 38,000, and 43,000 plants per acre. No significant yield differences between the 30-inch rows and twin rows occurred. Neither has there been any population interaction, except at the highest seeding rate. At 43,000 plants per acre, the twin rows win by about 3% in yield.

“Again,” says Coulter, “it’s pretty hard to beat 30-inch rows, especially at the normal populations we plant today. If populations keep going up in the future, maybe we’ll need to look at the spacing issue more closely.”

7. Consider genetics first.

Coulter says you really need to consider the corn brands (or hybrids) you plant. He’s done high-yield comparisons both by brand and by seeding rate.

“The top end for our very high-yield efforts is about 40,000 plants per acre, and 260 bushels an acre if the weather cooperates,” he says. “In our trials and observations, it looks like the most important thing in those situations is to first choose a brand that has the potential to respond to a high population.”

Yield differences between the best and worst hybrids in these trials ranged between 21 and 32 bushels per acre. The population effect on yield ranged between 9 to 31 bushels per acre.

“For people who want to push for the upper yields, I tell them to choose the right brand first, then pick the population that is right for that brand,” says Coulter.

8. Conduct strip tests.

On-farm test strips will verify optimal seeding rates. “With the current high seed costs and grain prices, it is critical to seed at the optimal rates to optimize yield and to maximize economic return,” he says.

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