Recently, university researchers conducted a three-year, six-state study nicknamed the Kitchen Sink study because of the vast array of inputs and agronomic practices they analyzed. When all the data was tallied, one factor stood head and shoulders above the rest when it came to improving yields in a single move.
Narrow rows. That’s it. No bags, no software, no mixing or blending. Just switching from 30-inch rows to spacing of 20 inches or less boosted soybean yields an average of 2.9 bushels per acre. That is greater than the 2.3-bushel yield bump that resulted from implementing a full program of fertilizer (both dry and foliar), inoculants, seed treatments and foliar fungicides on beans planted in 30-inch rows.
“Of all the newfangled things we looked at, row spacing gave us the biggest increase,” marvels Seth Naeve, the University of Minnesota Extension agronomist who led the Kitchen Sink study. “I think that’s really provocative for farmers.”
Data from Cornell University agronomist William Cox helps explain the phenomenon. In his New York population and row-width trials, Cox determined that soybeans planted in 7.5-inch rows had 15% more biomass, 14% more pods, 9% more seeds and 15% greater yield than the same variety growing in 30-inch rows.
That’s a lot more conversion of sunlight and carbon dioxide into soybeans. It’s also a great way to make sure your canopy closes promptly, shading out weeds and capturing moisture.
Despite the growing body of evidence that narrow-row beans out-perform wider-planted ones, the acreage of beans on 30-inch rows is actually increasing. Part of that shift to wide rows could result from the need to return to cultivating herbicide-resistant weeds like pigweed in some areas.
In other areas, the switch is presumably due to the convenience of maintaining a single planter for both corn and beans. Though that sounds like an economically understandable move, a 2008 study by Iowa State University found that the benefits of narrow rows justified the added expenses on as few as 355 acres with a 50-50 corn-soybean rotation.