This is the third time in his career that Ontario provincial cereal specialist Peter Johnson, has conducted trials on sulphur. After earlier trials in the early 1990s and again in 2000, he began again in 2011.
“The first two trials, we got no response to sulphur, except the occasional little blip — but on average there was nothing there,” said Johnson.
This was likely because Ontario is in the wind shadow of much Chicago and Michigan industrial development, conveyed Johnson. “That’s been referred to, in the past, as ‘acid rain.’ Farmers in Ontario really should refer to it as ‘foliar fertilizer.’
“Back in the late nineteenth century (1890-2000), if farmers wanted to grow wheat, they’d have to add some form of sulphur (as we were quite deficient). From the ’40s until now, we’ve had a sufficient amount from atmospheric deposition.
“Throughout the bulk of the twentieth century, we had enough sulphur without sulphur additions. That’s changed. We’ve brought in more and more environmental laws and efforts to improve air quality, and with that, we’ve seen our sulphur essentially cut by two thirds.”
Agronomists have often suggested applying a pound of sulphur for every 10 pounds of nitrogen.
“I don’t believe that ratio applies in Ontario conditions, because it would only apply if I got zero sulphur out of the air,” says Johnson “The key is simply to make sure there’s enough sulphur and nitrogen, and give credit to the sulphur from the air.”
Plants need sulphur to develop protein. Johnson and his team have been evaluating the quality of the flour from sulphur-added wheat, and have found that, “when sulphur is deficient, it definitely impacts the quality of the flour and yield of the crop.”
Sulphur is an important part of a total nutrition package. Johnson says, “If you’re sulphur deficient and you add too much nitrogen, in the extreme case you’ll actually reduce rather than increase yield.”
Oilseed crops need more sulphur than grains. Canola is very responsive to sulphur. “It’s a little harder to see in wheat,” Johnson says, “as it doesn’t have the same demand for sulphur.”
Typically, sulphur deficiency appears when the plant hits the rapid growth stage (stem elongation) when the greatest demand for sulphur and nitrogen occur.
“Sulphur and nitrogen deficiency look the same,” said Johnson. “It’s virtually impossible to tell the two apart. But, if you’ve already put on 90 or 100 pounds of nitrogen and you’re seeing nitrogen deficiency symptoms, it’s a pretty good chance it’s sulphur, not nitrogen, you’re lacking.
“Sulphur is a secondary nutrient while nitrogen is a macro-nutrient. Sulphur can’t photosynthesize properly or make corossol properly without nitrogen. Once you apply sulphur, the plant picks it up, fixes the deficiency, and away you go.
“How quickly that happens depends on how fast the sulphur gets into the soil. Using liquid sulphur with moisture present at the soil surface, it can rebound in as little as 48 hours.”
Johnson says the sulphur situation in Western Canada is very similar to that of North Dakota and Montana. Farmers in all of these areas have been applying sulphur to many crops for many years.
However, our soil bank account is significantly depleted, compared to what it was 40 or even 100 years ago.
“As you push for higher yields, you have a higher demand for all nutrients, not just sulphur,” says Johnson.
Johnson recommended using sulphate as opposed to elemental sulphur (which is cheaper but needs to be broken down by bugs). He also suggests applying sulphate in the spring as opposed to fall when it may leach out before it can be used.
Doon Pauly, agronomy research scientist at Lethbridge, Alta. says that it is common practice for farmers in southwestern Alberta to seed winter wheat on canola stubble.
Jeff Schoenau, a professor at the University of Saskatchewan says, “Significant amounts of sulphur can be released from canola residue the following year and any unused sulphur likely carries over quite well. As such, sulphur deficiency is unlikely to be a major issue, just as it’s not generally for spring wheat in many locales, especially southern Saskatchewan in brown and dark brown soils where sulphates are often present in the sub-soil.” †