The Buzz about Sulphur on Soybeans

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The yield benefit of sulphur is well-established in crops such as winter cereals and alfalfa. More recently, agronomists are promoting the nutrient’s benefit in corn. So what about soybeans?

Purdue University researchers reported an impressive yield response to sulphur on soybeans in Northwestern Indiana that set the industry buzzing. The verdict is still out, however, on sulphur’s response in Ontario’s soybean crop.

“With respect to soybeans, we don’t have enough data yet to say we should get excited about it,” says Horst Bohner, Soybean Specialist, Ontario Ministry Food, Agriculture and Rural Affairs (OMAFRA). Bohner and his colleagues conducted 10 trials across the province in 2018 and have more planned for 2019. He admits the dataset isn’t robust enough to make solid sulphur recommendations to Ontario soybean growers just yet.

“In 2018, most of the trials showed no statistical yield difference to the applications of 100 lbs/ac of ammonium sulphate. In my trials, the average yield response was 2.3 bu/ac. Michigan State did similar trials and showed no average yield response. I suspect after we have a bigger data set the average response to soybeans on soils with good organic matter will be small,” says Bohner.

Potential fit on sandy soils

The one observation he does acknowledge so far: “It seems that it’s on low organic matter soils, sandy soils, where we’re seeing the benefit.”

Jake Munroe, Soil Fertility Specialist – Field Crops with OMAFRA, explains most sulphur in soil is stored in organic matter. “If a field has been declining in its organic matter content over the past 20 to 30 years, that means there’s less soil-supplied sulphur,” he says. Soil type can also play a role. “Coarse-textured soils are more susceptible to leaching and have less of a nutrient holding capacity. Those soils have seen some economic response in sulphur applications to soybeans.”

While low organic matter can be one cause of sulphur deficiency in a field, the main contributor is the 50+ percent drop in atmospheric deposition of sulphur in Southern Ontario over the past few decades. Munroe cites stricter emission standards as one of the key reasons. “In Southwestern Ontario, we’ve basically gone from having atmospheric depositions in the range of 20 plus pounds per acre of sulfate sulphur in a given year to now being down to 5 to 10 pounds.”

Sulphur 101

So what does a sulphur deficiency do to a crop like soybeans? As Munroe explains, sulphur is necessary for two important amino acids. “If you’re deficient in sulphur, it's going to affect protein production in the plant. In terms of the deficiency symptom, it tends to show up as yellowing of the newer growth – of the younger leaves – as opposed to the older growth.”

Munroe theorizes that soybeans may not show as big of a response as winter cereals or alfalfa due to crop timing. “Because soybeans are typically planted later, the sulphur uptake is just going to be later in the season – that gives the soil an opportunity to warm up and mineralize and produce plant-available sulphur in good time to match up well with crop uptake.”

Stay tuned for results

More conclusive results will be available once research is carried out to evaluate sulphur response on soybeans during the 2019 growing season. Dr. John Lauzon in the School of Environmental Sciences at the University of Guelph will be conducting trials at the university research station. He has partnered with Munroe, Bohner and the team at OMAFRA to perform trials at several farm sites.

“It will be a decent number spread across various soil types in different parts of the province,” says Munroe. “Then we can speak from two years’ worth of experience.”

Soy Masters will report on the findings in winter 2020.