Understanding the yield gaps in soybeans is one of the first steps in improving yield and profitability.

Everyone wants to know what is causing gaps in yield. Why do everyday growers like Kip Cullers and Randy Dowdy produce 160- and 170-bushel soybeans? Why do Illinois producers Dan Arkels and Robert and Jason Lakey break 100-bushel soybeans and join the ever-growing team of growers who have broken the 100-bushels ceiling?

It wasn’t that long ago that we were happy to hit 60- or 70-bushel yields. Now we want 70 and 80 bushels. Maybe in 5 or 10 years that will move up to 80 to 90 bushels. Soybean yields no longer seem stagnant and average yields are on the rise.

University researchers across the Corn Belt decided to evaluate what is causing the yield gaps in soybeans. You probably have heard the plea go out from Emerson Nafziger the last few years to complete a detailed survey. Nafziger posted two requests for completing this multistate, detailed survey in January and March 2017 at “Calling Illinois Soybean Growers-Again.” This survey was funded by the North Central Soybean Research Program (NCSRP).

Nafziger wrote in his blog post, “The most useful way I’ve heard this project described is as a search to find what we should work on next with regard to soybean research. The goal is to have thousands of fields in a large database, then to see how soil, weather, and management interact to produce yield.” Well, initial results have been released in a preliminary format at the NCSRP website: Assessing Causes of Soybean Yield Gaps in the North-Central Region of the U.S.

Patricio Grassini, University of Nebraska, and Shawn Conley, University of Wisconsin-Madison, wrote that, “Yield potential is the yield of a specific variety when grown in an environment to which it is adapted, with a non-limiting supply of water and nutrients, and with pests, weeds, and diseases effectively controlled. Under these optimal conditions, crop growth is determined by solar radiation, temperature, atmospheric carbon dioxide concentration, and management practices such as sowing date, cultivar maturity, and plant density.”

While that is true, I don’t believe that this statement covers all the possibilities. It is becoming increasingly clear that when you remove all stress while stimulating the plant beyond what it is naturally capable of, you can define a new yield potential. I remember how university specialists believed the theoretical highest yield in soybeans was 100 bushels per acre and then along came Kip Cullers who showed us that providing that little extra, beyond removing stresses and having ample nutrients available, makes a big difference. Limiting yourself to defining gaps caused by limits in temperature, water, light, carbon dioxide and nutrients, greatly shortchanges soybeans’ yield potential.

With checkoff funds provided by NCSRP and Nebraska and Wisconsin soybean checkoffs, the authors collected data on soybean yield and management practices over 2014 and 2015 from 3,568 fields in Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Nebraska, North Dakota, Ohio and Wisconsin.
82 percent were rainfed and 88 percent had corn as the previous crop, except where soybeans were grown after wheat or soybeans.

The authors reported that soybean yield gaps over these two seasons were relatively small, averaging 22 percent (rainfed) and 13 percent (irrigated) of their yield potential. The yield gap was larger in rainfed than irrigated areas, which is what we would expect.

The authors concluded that planting date was the most consistent factor explaining the gap in yield. Other practices that explained variation included tillage, plant protection (season foliar fungicide or insecticide application) and drainage. Aside from drainage, which most growers recognize as the one of the best practices they can adopt, early planting and foliage protection are key, high-yield strategies along with seed treatments.

While the researchers set out to research and identify yield gaps, the first look at the data really hasn’t uncovered anything new that isn’t already being researched. Yet I support their efforts to find what’s causing gaps in yield and use this information to strategize research and extension programs. I always wonder where the next big breakthrough will come in soybean management.

Soybean agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com or ring him at 402-649-5919.