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Wide rows for soybeans

Planting soybeans in wide rows comes with plenty of advantages: producers can use a single piece of equipment for planting corn and soybeans. Seed costs are lower with reduced seeding rates. And increased airflow between the rows means reduced white mould pressure. 

But is wide-row planting a silver bullet for growing better soybeans? Not necessarily, says Horst Bohner, provincial soybean specialist for the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA).

Last year was the first year of a three-year study led by Bohner at Elora, Bornholm, Winchester and Ridgetown research stations, comparing 15-inch and 30-inch rows. Dupont Pioneer also replicated the studies in several eastern Ontario locations.

“There's this notion that if you grow soybeans in wide rows the beans have more opportunity to take advantage of inputs because individual plants have more space,” Bohner says. “But it's not correct. The biggest outcome of the study was that variety selection was far more important than row spacing for high yields.”

In Ontario, most soybean acres are seeded in narrow (7.5-inch) or intermediate (15-inch) spacing. But yields tend to decrease in 30-inch rows- up to five bushels less per acre, according to Bohner. His study aimed to determine whether the yield gap could be closed with management practices and the promotion of early growth with starter fertilizer.

According to Bohner, the results varied by location. At Elora, the yield lag could be “won back” via management practices such as strip tillage and the use of inputs at the beginning of the season. “At the end of the day what we showed was somewhat surprising - we could get the yield gap back fairly easily, and wide rows yielded equivalent to narrow rows if we gave them inputs,” he says.

At Bornholm, the narrow rows did better than the wide rows, but the team had the acreage to try a range of varieties. “The outcome there was to choose the best yielding variety and put no inputs on the soybeans. That was by far the most profitable scenario,” Bohner says.

By comparison, data from the Dupont Pioneer plots showed a slight yield increase for 30-inch rows.

Paul Hermans, an area agronomist for Dupont Pioneer in eastern Ontario, says the plots in the study yielded an average of 62.1 bushels per acre in the 30-inch rows, while the 15-inch rows yielded 60.1 bushels per acre on average.

But Hermans says conditions were very good across eastern Ontario in 2015, with yields 15 to 20 per cent higher than normal for all beans. “I attribute the results to the growing environment,” he says.

He echoes Bohner's claim that variety has a significant impact on performance. “We picked the varieties that tend to branch more and do well in both 15- and 30-inch rows,” he says.

Tips for 30-inch rows

“When it comes to wide rows, you want to choose a variety that's adapted for that - it needs to be a tall, bushy variety that branches well. There's no question there are big variety differences,” Bohner says.

Hermans says seeding rate is another key concern.

“Variety and seeding rates go hand in hand - you can go to a wider row and get more air space between the row, but if you keep the same seeding rate the plants get closer together within the row. You've got to look at where your seeding population is within the row and look at seeding rate to cover both aspects,” he says.

Overall, Hermans recommends lower seeding rates, and earlier planting dates, as his trials demonstrated that early planting yielded more than later planting, regardless of frost.

Bohner adds that planting early allows the canopy to close before too much solar radiation is lost. For growers opting for 30-inch rows, Bohner says a good plant stand is necessary. “You can't afford to have gaps in the stands.”

He also recommends doing a soil test prior to planting; if nutrients are slipping, fertilizer should be put down with the planter or broadcast before planting.

If growers are still on the fence about switching to 30-inch rows, Hermans says the decision totally depends on the situation.

“It should go on a case-by-case scenario,” he says. “If you're a grower that just went out and bought new equipment last year for 15-inch rows, and you're happy with what you have, why change? If you've got 7.5-inch rows and the equipment is wearing out, and you want to use one machine for two jobs, maybe I'd look at 30-inch rows.”

But the occasional experiment can also be a positive business decision. “I always say to the guys that the definition of insanity is doing things the same way over and over and trying to get different results,” Hermans says. “I try to encourage my guys to try a few new things every year on some acres to see if they can increase yields or reduce input costs.”

April 12, 2016  By Julienne Isaacs