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Narrow-row beans once were going to revolutionize soybean production, but have we backslid?

Personally, I think the evidence is clear that maybe 6 to 7 years out of 10, narrow-row beans will out yield beans planted in 30-inch rows. But then again, 3 or 4 years out of 10, 30-inch row beans will yield the same or maybe higher. Sometimes it is difficult to believe which row spacing is better.

The earlier you plant beans the less likely you’ll see a consistent benefit, and the later you plant soybeans the more likely you’ll benefit from narrowing row spacing. If you plant from mid-April to mid-May, narrow rows won’t always win out. From mid-May to mid-June, narrow rows will usually prevail. After mid-June and into July (double-cropped beans), narrow rows almost always win. I think that pretty much sums it up.

Farmers used to plant soybeans in rows (30- and 38-inch) or drill them. Then, by the 1980s narrow-row soybeans became popular as a means of weed control since the canopy closed over the rows sooner, suppressing weed control. In those days, growers needed as much help controlling weeds as possible since herbicide options weren’t perfect.

For example with 7.5-inch rows, the canopy closes about 30 to 35 days after emergence during normal growing conditions, 15-inch rows in 40 to 45 days and 30-inch rows in 50 to 55 days. A full canopy handles later-emerging weeds pretty well, and a number of species now emerge over a longer time frame and may be missed with a post application.

Then, along came Roundup Ready soybeans and glyphosate and weed control was a no-brainer. Growers quit drilling beans, went to larger planters and dropped seed rates and row spacing—for the most part—widened out to 30 inches again over the last 15 years. But each year we still read reports that narrow rows pay.

Twenty years ago Ellsworth Christmas, Purdue University’s extension agronomist, and Dick Cooper, USDA agronomist and soybean breeder at Ohio State University, were promoting narrow-row soybeans and predicted it would drive the next revolution in soybean production. In fact they predicted it was going to continue to edge upward a bit, even after the introduction of Roundup Ready soybeans and the accompanying improvements in seeding mechanisms on drills (think place seed instead of pour seed). However, it seems we have backslid.

Since 2000, planter technology has advanced rapidly with precision placement and spacing to meet the needs of corn. While soybeans still benefit from more even stand distribution, it has been questionable if narrow rows are justified, considering that farmers want 40- and 60-foot planters and do not want the expense and weight of all those extra row units that come on a split planter.

Ellsworth Christmas once wrote that “Indiana growers expect about a 15-percent yield hike compared to 30-inch rows in the northern third, possibly the northern half, of that state. In the southern half, that drops to around 12 percent. In northern Corn Belt states, such as Wisconsin, some studies have produced yield hikes of up to 18 to 20 percent for drilled beans. In areas far enough south to double-crop beans after wheat, 18- to 20-percent yield increases over 30-inch rows are common. With 15-inch rows possible with planters, there's a definite yield gain over 30-inch rows. On average, however, figure 15-inch rows will gain you two-thirds to three-fourths of the potential yield increase from drilled beans.”

I don’t advocate adopting drills to move narrow rows and 7.5-inch rows. There are a lot of row units and a lot of moving parts to maintain. Instead I would advocate for moving to 15- to 20-inch rows and planting as early as is reasonable when the soil and season is ready.

Narrow-row beans pay off more times than not, but having separate planters for corn and beans probably doesn’t pay today. Maybe 20-inch spacing is the answer instead of 15-inch spacing. Many growers feel 15-inch corn is difficult to manage, but 20-inch corn is not and 20-inch spacing is good for soybeans. I would put moving to narrow-row beans high on your management list. Certainly, buying into a way to narrow rows to at least 20-inches should become an important decision.

Post a comment in the box below and let us know what spacing you plant at and how you feel about the viability of moving to narrow-row soybeans.

Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com.