Narrow advantage for narrow rows
In theory, corn should be grown in rows less than 30 inches apart. That's because in narrower rows the plants are farther apart within the row and, therefore, compete less with each other for light, water, and nutrients. Equidistant planting would seem ideal.
In reality, however, there usually isn't much yield difference between 30-inch rows and narrower rows except in the northern Corn Belt and in other regions when fertility or water are in short supply.
“Narrow rows may be most beneficial where canopy development and yield are challenged by marginal soils or climates,” says Purdue University agronomist Bob Nielsen. He offers five examples.
● Northern climates where it is cooler and there is less growth.
● Nutrient-deficient soils, especially if nitrogen is lacking.
● Sandy, nonirrigated, often droughty soils.
● Shorter-season hybrids.
● Smaller, shorter, less leafy hybrids.
Silage corn also does well in row widths less than 30 inches.
Narrow rows give individual plants a lot more space. At a population of 36,000, individual plants in 30-inch rows are 5.8 inches apart within the row. At that same population, plants in 20-inch rows are 8.7 inches apart within the row, while plants in 15-inch rows are 11.6 inches apart. Plants in twin rows (8 inches apart on 30-inch centers) are also 11.6 inches apart within the row. If the plants in the twin rows form a diamond, there are 9.9 inches between plants in adjacent rows. (See the diagram on page 52.) The corn on the opposite page is in 15-inch rows.
According to most research and farmer experience, narrow rows (less than 30 inches) usually yield better than 30-inch rows north of Interstate 90, which runs a few miles north of the Iowa/Minnesota border. University of Minnesota agronomists say research in southern and central Minnesota shows that corn in 20-inch rows can increase grain yields by up to 7% to 9% compared to 30-inch rows.
Greg Stewart, a corn specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs, says research in the 1990s showed twin rows could outyield 30-inch rows and were sometimes equivalent to 15- and 20-inch rows. However, there was no yield difference at some sites. When the results from several studies at several populations and in several locations were averaged, twin-row corn yielded 6 bushels better in Canada. That was a 5% to 6% increase over 30-inch rows.
But across the heart of the Corn Belt, yield advantages are typically small and inconsistent, unless there are water and nutrient issues. (Most likely, the majority of row-width research has been done in medium- or high-yield environments.) However, there is rarely a yield penalty for using narrower row widths or twin rows. That's an important consideration for farmers who want to grow other crops, most notably soybeans, in narrow rows.
Nielsen says, “Thirty-inch rows are not a primary limiting factor for corn grain yield today in the heart of the Corn Belt. If there is more than enough water, nutrients, and light, then you are not likely to see a significant response to narrower rows.”
There was a flurry of interest in and research about 15- and 20-inch rows in the mid-1990s. More recently, attention has been focused on twin rows. Although it takes a special planter to plant twin rows, they can be harvested with a 30-inch corn head because the pairs of rows are 7 to 8 inches apart on 30-inch centers.
Twins Vs. 30s
In 2009, Monsanto compared twin rows to 30-inch rows at 28,000, 33,000, 38,000, and 43,000 plants per acre at 20 locations, most of which were in the Corn Belt. Twin rows yielded an average of 3 bushels more per acre.
In 2010, Pioneer Hi-Bred compared twin rows to 30-inch rows on commercial farms in 179 comparisons at 31 locations. Most of the farms were in Illinois, Iowa, and Minnesota, but some were in Colorado, Indiana, Kansas, Missouri, and Ohio. Twin rows had an average yield advantage of .7 of a bushel per acre over the 30-inch rows.
Also in 2010, Beck's Hybids, based in Indiana, compared three hybrids at populations ranging from 24,000 to 48,000 plants per acre in 20-inch, 30-inch, and twin rows. In 30-inch rows, the average yield for the three hybrids at various populations was 174.3 bushels per acre. In 20-inch rows, the average yield was 161.9 bushels per acre. In twin rows (8 inches apart on 30-inch centers), the average yield was 167 bushels per acre.
While a lot of the twin-row research has been done by private companies, much of the earlier narrow-row corn research was conducted by universities. Nielsen says, “Most public research indicates that yield response to row spacing narrower than 30 inches is generally positive, but very inconsistent.” He says the increase from narrow rows averages 1.5% to 2.5%.
Some of the early research on 15-inch rows was flawed by planting into wheel tracks or doubling back and driving over planted rows.
Because the above-ground portion of a corn plant is competing with its neighbors for light, many agronomists, plant breeders, and farmers have expected narrow rows to outyield 30-inch rows. That's because the narrower rows canopy sooner and enable the corn plants to intercept more light. But many scientists have concluded it isn't necessary for corn plants to capture additional light early in the growing season.
“If we think of the crop as a yield-producing factory, sunlight is the fuel that powers it,” says University of Illinois agronomist Emerson Nafziger. “The factory needs to be at full speed, with a full light-gathering roof (crop canopy) by pollination time in order to produce maximum grain yields.
These diagrams show spacing between rows and within rows at 36,000 plants per acre.
“Because the crop is growing so rapidly by stage V8 to V9, corn in narrow or twin rows does not have a very large or lasting advantage over 30-inch rows in the rate at which the plants increase leaf area and sunlight interception,” says Nafziger. “While any such advantage is often positive, the difference in total sunlight intercepted by wide and narrow rows by the time plants reach full canopy is relatively minor – probably less than 10%. Pollination success and yield are determined after full canopy. And by then there is often no difference in light interception between wide-row and narrow-row corn.
“It's clear that while sunlight has an effect on productivity, as a factor it appears it is usually less important than temperature and rainfall,” he adds. “These factors are all correlated to some extent, making it difficult to single out the most important factor in determining yield.”
There's a school of thought that substantially higher populations – 40,000 or more – will be needed to increase yields and that narrower rows will be needed to accommodate these higher populations while maintaining stalk quality.
In 2005 and 2006, Pioneer compared twin rows and 30-inch rows at 36,000, 42,000, and 48,000 plants per acre in Iowa and Nebraska. Mark Jeschke, agronomy research manager, says, “These studies showed no performance advantage of twin rows over 30-inch rows at high populations.”
He adds that on-farm trials in 2010 “also found no effect of plant population on twin-row yield performance relative to 30-inch rows.”
Those comparisons were made at 14 sites in Illinois, Iowa, and Minnesota at populations ranging from 34,000 plants per acre to 42,000.
In 2009, Ohio State University was part of the multistate evaluation of twin-row corn supported by Monsanto and Great Plains Manufacturing. Three maturities of corn were used (107-day, 111-day, and 112-day) at four plant populations (28,000, 33,000, 38,000, and 43,000 plants per acre).
“Grain yields of twin-row and 30-inch corn (180 vs. 182 bushels per acre) averaged across the three hybrids and four plant populations were not significantly different,” says Ohio State agronomist Peter Thomison. “Although a small but significantly higher yield (approximately 5 bushels per acre) occurred when plant populations were increased above 28,000 plants per acre, twin and 30-inch rows exhibited similar responses to plant population.”
From 2005 through 2007, University of Minnesota researchers compared 20-inch rows to 30-inch rows for one full-season hybrid at populations ranging from 20,000 to 40,000 at Lamberton and Waseca. The study showed no yield advantage for narrow rows and indicated that the optimum population is similar for both row widths.
In 2008, they compared four hybrids in 20-inch rows and 30-inch rows at the same sites and same population levels. As in the earlier study, they found that optimum population is not affected by row width. However, yield was 9% higher with 20-inch rows in 2008.
Another question with lots of ramifications is whether some hybrids are more suited to twin rows than others. According to Pioneer's Jeschke, “Twin-row studies that have included multiple hybrids generally have found no difference in response to row spacing.”
In 2010, Pioneer conducted on-farm twin-row studies at several locations with multiple hybrids. Among 14 current hybrids that were tested at three or more locations, no significant differences in yield between twin rows and 30-inch rows were observed, nor were any hybrid by-row spacing interactions observed among hybrids compared at multiple locations.
Brisk equipment sales
For many farmers, decisions about twin rows boil down to equipment costs. Both Great Plains and Monosem market twin-row planters as well as planters for other row widths.
Tom Evans, vice president of sales for Great Plains, says on a new planter you can expect to pay about $2,000 per row for the extra row units needed to plant twin-row corn. “If you are growing 200-bushel corn, you can expect a 4% yield increase,” he says. Twin-row planter sales have “doubled about every year,” he adds.
Don Niehs, sales manager for Monosem, says there is a lot of interest in twin-row corn, and that interest is translating into sales.
“There has been tremendous growth of sales of twin-row planters over the last two or three years,” he says. “It is our opinion that the future is not going to be in 30-inch single rows.”