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Plant More Seeds with Narrow Rows

When seed company sales representatives extol how modern hybrids yield much more than past ones, they’re right. Since the mid-1950s, U.S. corn yields have annually increased 1.9 bushels per acre. 

Most of this gain doesn’t lie within the seed, though. You are mainly planting them thicker.  
“Corn breeding has been aimed at plants per acre, not yield per plant,” says Roger Elmore, University of Nebraska agronomist. “You are actually trying to squeeze the most seeds you can within 30-inch rows.”

There’s a limit to this, as high populations within 30-inch rows can adversely impact the amount of plants that silk during pollination.

There’s a way, though, to plant more seeds without squeezing them in a row. Narrow rows (those spacings ranging from 12 to 20 inches) spread more seeds across a field. In the case of 12-inch rows, plant populations have zoomed up to 60,000 plants per acre (ppa) in testing done by the Stine Seed Company, Adel, Iowa. The equidistant spacing enables hybrids to better access water, nutrients, and sunlight – and then yield more, say company officials.

That’s the theory, anyway. This hasn’t always worked. Optimal yields require that corn plants garner 95% of a sunlight measurement – 
photosynthetically active radiation (PAR) – before and after silking. University trials conducted in the 2000s in Illinois, Nebraska, Indiana, Minnesota, and Michigan found that narrow and twin rows boosted this kind of light interception during vegetative growth stages. By the time the plants reached silking, little or no difference in light interception existed between 30-inch and narrow rows. Narrow corn rows will not increase yields in cases like these.

Genetics matter
Genetics may play a role in this, though. As 30-inch rows have become the norm, corn breeders have focused on hybrid performance for this row spacing.

“You can’t take the same old genetics and push up populations and expect more return on investment,” says David Thompson, national marketing and sales director for Stine Seeds. “You need to take genetics that are built for high populations.”

Such genetics exist. Back in the 1970s, Thompson explains, most seed companies intentionally overplanted their corn trials. Later, company workers would come back and hand-thin them to ensure that picket-fence spacing resulted.

Harry Stine, founder of Stine Seeds, differed with that strategy. He reasoned that breeding is a numbers game, with just several hybrids out of initial hundreds making the cut to market each year. Given a choice between perfectly manicured plots or more corn hybrids to test, Stine opted for more hybrids.

He reasoned that poor standability would surface sooner in thickly planted plots. Thus, he could cull hybrids prone to lodging during testing.

This had another perk. “When you do that for 40 years, you develop genetics adapted to high populations,” says Thompson.

12-inch rows
Populations at 40,000 ppa and above benefit from the spreading out made possible by 12-inch rows.

“This gives equidistant spacing,” Thompson says. “Ideally, we wanted to plant in 10.5-inch rows. The reason we went with 12s is because that is as narrow as any corn head is made right now.

“There are not a lot of hybrids out there that will tolerate 12-inch rows,” Thompson adds. “Lots of these hybrids tend to be not taller than 6 or 7 feet tall. We wanted something that would stand – not lodge and fall over. They have upright leaf architecture, with pineapple leaves so they can reach for sunlight under high-planting densities. Generally, they are more disease resistant, since they are under a lot of stress due to higher populations.”

In 2012, Stine planted 2,300 acres to 12-inch row corn. One such Stine hybrid, 9733 VT3 Pro, had its highest return on investment up to 60,000 plants per acre. Thompson says several other Stine hybrids fit this profile.

It expanded in 2013 by planting all of the farm’s 15,000 corn acres to 12-inch row corn.

Lessons learned
Thus far, two lessons have emerged. “Increasing population in any sort of narrow-row configuration, 20 inches or less, works well as long as you have the right genetics,” says Thompson.

Most of Stine’s replicated trials also showed that corn hybrids spaced 12 inches apart yielded more in most cases compared to 20-inch rows at populations above 40,000 ppa.

“This was a bit of a turnabout, because we thought that row width was nothing but a means to an end,” says Thompson. “By itself, it was not a function of yield. Now, even at the same population, moving to narrow spacings may give you a yield benefit.”

That’s contingent on population, though. Results were more variable for hybrids planted on 12-inch rows at normal central Iowa planting rates of 30,000 to 35,000 ppa.

“When we planted up to 45,000 plants per acre and above, there was definitely a gain for 12-inch rows,” says Thompson.

He says a 6-bushel-per-acre yield boost is needed to justify the shift to high-density corn. Based on results seen so far, he says this is obtainable.

Stine uses a prototype 12-inch planter from John Deere. Bauer Built Manufacturing Inc., a Paton, Iowa, firm purchased by Deere in 2013, has built several 12-inch-row planters.
So far, 12-inch-row planters haven’t been an equipment challenge.

“Where the hang-ups have been are at harvest,” says Thompson. “That’s kept farmers from adopting it.”

Calmer Corn Heads, Alpha, Illinois, has manufactured 12-inch-row corn heads. With no other manufacturer building such a head, concerns surfaced about there being no harvesting alternative if a combine with a 12-inch head would break down.

That led Stine to modify its narrow-row corn strategy by shifting to 12-inch twin rows. It consists of 12 inches between each twin row and 8 inches between each twin-row set.

“The big benefit is that you can harvest with a 20-inch head,” Thompson says.

Both Deere and Calmer make 20-inch heads, so this opens up more combine options. This still makes efficient use of the spacings, but it makes it easier to adopt, he says. 

“Twin 12-inch rows will help speed adoption of high-density corn,” says Thompson.

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