As a retired USDA–ARS soybean breeder and production researcher, I say hats off to Missouri farmer Kip Cullers for taking soybean yields to levels we only dreamed about a few years ago. Clearly, Cullers studies every aspect of soybean management and uses every management tool to ratchet up yields another notch.
Closer to my home in Ohio, I’ve noticed farmers making some changes that I fear may prevent them from maximizing soybean yields. I’ve been told there’s a trend among farmers to abandon their 7"-row soybean drills in favor of unit planters. I also have observed fewer drills as I drive around Ohio during planting season.
I can’t argue with that logic because a unit planter lets farmers reduce their seeding rate. They can plant more acres in less time, if their planter is wider than their drill.
Back to wide rows? What disturbs me is that some farmers have told me they went all the way back to 30" soybean rows. One Indiana grower told me farmers in his area are moving from Group III to Group IV soybeans to maximize yield in 30" rows.
All those farmers told me their 30"-row soybeans yield just as much as their drilled 7"-row soybeans did. But unless a farmer feels he has to plant in 30" rows because of a white mold problem, using rows that wide is a mistake that may cost him yield.
My research always showed a significant yield increase for 7"- and 15"-row soybeans compared with 30". (The 7" rows yielded more than 15" rows, but I won’t argue if a farmer wants to sacrifice that additional yield for the advantages of a unit planter over a drill.)
My studies were conducted in the 1980s and 1990s. But more recent research, including the Farm Journal Test Plots, also shows a yield advantage for 15" rows compared with 30".
If a farmer isn’t seeing a yield increase when he moves from 30" rows to 7" or 15" rows, he needs to spend more time searching for varieties that respond to narrower row widths. In fact, farmers need to look for varieties that respond not only to their preferred row width, but to environments in individual fields.
No one-size-fits-all. The table below, drawn from my research, shows how differently varieties can respond to row width and environment. In the study, the normal-yielding environment approximated a farmer’s field. In the high-yield environment, yield-limiting factors were removed as much as possible by building up fertility levels and providing irrigation.
In the normal yield environment, when planted in 30" rows, the two varieties yielded the same. But in 7" rows, one variety increased its yield by 5 bu. per acre, while the other variety increased its yield by 10 bu.
In the high-yielding environment, in 30" rows, both varieties were similar in yield. In 7" rows, the taller, bushier, traditional variety gained 10 bu. per acre. But the earlier-maturing, shorter, less bushy plant (which I bred specifically for narrow rows and high-yield environments) increased its yield by 25 bu. per acre.
I’m not suggesting you should plant the semi-dwarf varieties that I designed in the 1980s for 7" rows and used in that study. But there is no one-size-fits-all variety, and selecting varieties that perform best in your row width and field environment can help you reach the next yield level. (And I hope you will think twice about going back to 30" rows.)
Also, soybean breeders need to give farmers a choice. Growers who want to plant soybeans in 30" rows to take advantage of lower seed and machinery costs need to develop varieties that maximize yields in 30" rows. By the same token, growers who want to take advantage of the higher yield potential of 7" and 15" rows need to have access to varieties that thrive in the narrower row spacings.
Editor’s note: During his career with the USDA–Agricultural Research Service, Richard Cooper worked as a soybean breeder and conducted production research. He was among the first scientists to achieve soybean plot yields of 100 bu. per acre, using varieties that he created. Although retired, he still keeps up with production agriculture.