GUELPH — What’s it take to grow a “sizzling” soybean crop? Soil plays a key role, naturally, but experts at the 2023 Ontario Agricultural Conference admitted that relatively little is understood about the below-ground processes that ultimately deliver all-important water and nutrients to the roots of the plants above.
OMAFRA soybean specialist Horst Bohner and Michigan soybean educator Michael Staton delved into the soil conundrum after presenting more typical “above-ground” data on when to plant, how much seed to plant, what varieties to plant and what chemical fertilizers and pesticides to apply.
It was Bohner who illustrated the soil information gap while reporting the results of a 2022 study from the University of Guelph’s Elora facility. The study demonstrated that irrigated, intensively managed soybeans (getting fertilizer and fungicide) yielded well, at 77.9 bu/ac, but did not yield as well as soybeans with exactly the same management regime that were grown without soil. The researchers instead planted the latter group in a mixture of peat and sand and yielded an astounding 88.2 bu/ac.
“That’s pretty exciting in terms of trying to understand whether the (performance) issues are above ground or below ground,” observed Bohner, who acknowledged that “obviously, what really matters is below the soil’s surface, and that’s where it gets really hard … and nobody really understands the soil anyway. So that’s where … it gets difficult.”
That reality “pains me greatly as a soybean agronomist because the truth is, all the stuff that we often talk about is above ground, it’s seeding rates, it’s fungicide, it’s stuff we can see,” he said.
The study showed an even more profound performance for the soil-less soybeans when the researchers discounted individual plants that got infected with a stem canker because of their unusual circumstances. In that case, the researchers estimated the yield at 129.2 bu/ac, reaffirming what plants can really do “if you take away the limitations of the problems we have with the soil.”
When asked how farmers could make headway against the mysterious limitations of soil — and a speculated restriction on plant roots within the soil — Bohner didn’t have much to offer. “I don’t want to sound silly when I say it, but it really is true: No one has a good handle on soils. Even our soils people (at OMAFRA) will admit there’s a lot of stuff going on below ground that we just don’t have a good handle on.”
He seemed to reject the idea that conventionally tilled soybeans would allow for much better root performance in the soil over low-till soybeans, estimating the general yield difference at just 2 bu/ac.
Staton suggested keeping soil compaction to a minimum, along with erosion control, as the best approach to keeping soil in optimum physical condition for plant roots. He qualified those two physical soil concerns as different from the usual biological concept of soil health. “If we’re not paying attention to those two big categories, I don’t know why we’re talking about soil health,” Staton said.