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Boost Plant Population with Twin-Rows

By: Gil Gullickson

Benefits from game-changing technology often aren’t immediately apparent.
“When it was predicted in the mid-1980s that everyone would have a computer on his or her desk and it would change the way we live, no one had any idea how far reaching it would be,” says Steve Legg, a Windfall, Indiana, farmer.

Legg, whose family has conditioned seed for Stine Seed for 30 years, sees converting from 30-inch corn rows to twin-row 20-inch spacings as another game-changer. This concept spaces twin corn rows 8 inches apart with an 12-inch gap.

This builds upon 12-inch row spacings that Stine has researched in recent years. Twelve-inch rows equidistantly space seeds so plants may better access water, nutrients, and sunlight, says David Thompson, Stine Seed Company national marketing and sales director. Theoretically, this should boost yields.

One drawback is the need for specialized planting and harvesting equipment. That’s nixed by the twin-row 20-inch spacings that allow use of 20-inch equipment like narrow-row corn heads while still ensuring equidistant spacing. The system also uses tramlines for subsequent spraying or sidedressing trips.

The twin-row 20s key an even more crucial component.

“Our theory is that row width by itself is not really the key,” says Thompson. “We are trying to boost yields by high populations. In order to get to high populations, we have to go to narrow rows.”

Several years ago, Stine researchers observed that U.S. plant populations and average corn yields are now about fourfold higher than back in 1930. Both levels rose lockstep with each other.

Closer analysis revealed corn plants in both 1930 and 2014 produce about the same amount of grain per plant (.33 pounds). Thus, Stine researchers concluded, yield gains are largely due to quadrupling of seeding rates.

High-pop hybrids

There’s industry buzz about U.S. farmers growing average 300-bushel-per-acre corn yields by 2030. If the yield-plant population relationship continues as it has the past 80 years, though, average seeding rates need to be around 50,000 plants per acre (ppa). Few hybrids can now endure these rates in tight 30-inch rows.

“We have reached a point with populations in 30-inch rows where the roots and plants compete with each other,” Legg says. At 60,000 ppa, for exampleplants in 30-inch rows would have just 3.5 inches of room between them. In twin-row 20s, they’d have 8.7 inches.
Stine believes it has hybrids well-designed for higher-than normal populations in twin-row 20s. In the 1970s, most seed companies intentionally overplanted corn trials, says Thompson. Later, they would hand-thin them to ensure picket-fence spacing.

Harry Stine, founder of Stine Seed, thought testing more hybrids in more plots was time better spent than having perfectly spaced plants in fewer plots. Testing more hybrids increased the odds of more of them making the market. Meanwhile, hybrids prone to lodging in thickly planted plots would soon exit from Stine’s hybrid lineup.

This strategy had a side benefit, says Thompson. Over several decades, Stine developed genetics well adapted to high populations planted in twin-row 20s.

These plants tend to be shorter than most hybrids at 6 to 7 feet tall and are more upright in leaf architecture in order to capture more sunlight. Good standability and strong roots also enable them to withstand thick seeding.

Ideal seeding rates for Stine hybrids vary, depending on row spacings and genetics. Seeding rates are 100% to 130% of  of their normal 30-inch row populations in twin-row 20s. Adding more plants means more management and especially more nitrogen (N).

“In Indiana, we have lots of soils low in cation-exchange capacity,” says John Thacker, a Freedom, Indiana, farmer and Stine dealer. “They don’t have high water- and nitrogen-holding capacity. So, we’ll put down 50 to 60 pounds of actual N in urea preplant, 3 to 5 gallons per acre of pop-up starter fertilizer with the planter, and then sidedress the rest of the N at the V5 to V6 stage with urea and Agrotain over the top. We cannot take the chance of running out of N with our soil types.” 

More plants also mean more residue. Legg plans to use a Great Plains twin-row planter equipped with no-till coulters to no-till corn in soybean or wheat ground. There may be a need for vertical tillage following corn harvest to further eliminate residue.
Equipment expense can be minimized (a bit) if you are trading planters anyway. Bruce Leas, Bluffton, Indiana, had separate corn and bean planters with box units that he upgraded to a central-fill planter with spacing flexibility. “If twin 20s don’t work, I can go to twin 30s or 20-inch spacings,” he says.

Does it pay?

Questions remain about the strategy, though.

“Higher corn yields have been driven in large part by a continuous linear in­crease in plant population year after year,” says Mark Jeschke, DuPont Pioneer agronomy research manager. “There is a general sense out there that as populations get higher, nar­row rows are needed to spread out plants and reduce crowd­ing in the row. There is lots of intuitive appeal to this, and it is one reason we keep coming back to it. The other part of this is creating a hybrid suited to narrow rows.”

That’s where the hang-ups begin. The vast majority of industry and university studies show no positive hybrid-by-row spacing-by population interaction, says Jeschke.

Typical is a 2014 study by Beck’s Hybrids that plantedfour hybrids – two of Beck’s and two Stine ones groomed for high populations – in twin-row 20s at 60,000 ppa vs. 30-inch rows at 34,000 ppa.

The Beck’s numbers planted in narrow rows at high rates yielded below what they did in 30-inch rows at 34,000 ppa, or did not cover the increased seeding rate.

One Stine high-population hybrid yielded more in the narrow row-high population system, but missed covering the extra seeding cost by $3.72 per acre.  One of the Stine hybrids did have nearly a 40-bushel-per-acre yield boost and a $72-return-on-investment increase from planting it in twin-row 20s. These results are from one location with two replications in one year, reminds Toby Ripberger, Beck’s Hybrids practical farm research coordinator. Plans are to repeat the trial in 2015.

Thompson  says this trial proves Stine’s point that high populations in twin-row 20s are rooted in genetics. At worst, its high-population hybirds nearly broke even with narrow rows and high populations compared to 30-inch spacings and normal populations. At best, it showed a significant return on investment.The 60,000 ppa rate is also higher than what Stine now recommends, he says.

Performance also hinges on weather patterns and fertility. “One thing we learned this year was where we had good but not excessive moisture and well-timed nitrogen applications, a good return on investment resulted,” says Thompson. “Where N timing was off, we didn’t get the yield bump needed.”

In many parts of Missouri, 2014 weather was ideal. “Our twin-row 20 configuration produced stellar results, often 20 to 30 bushels per acre better,” he says. “In Iowa, it was actually too cold to produce high-powered performance when we increased the population. When proper N timing did not occur, per-acre returns from the twin-row 20s did not cover the extra seed cost.”
A high population-narrow strategy will not work everywhere, says Ripberger.

“Make sure you get the correct genetics on the right soil type and at the right population,” he says. 

Legg says the system’s yield and profit potential are prompting him to switch.
“I’ve seen a lot of things come and go in the seed industry, and this one is going to stay,” he says.

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