Say you’re walking through your wheat field and spot some yellowing on upper leaves, but the lower ones look fine. What’s your diagnosis?
If you said sulphur deficiency, you’d be correct. Sulphur is not mobile in plant tissue, so if your crop is short on S, newly emerging leaves can’t suck it up from older leaves. It’s the opposite of nitrogen deficiency, which shows up on lower leaves because it is highly mobile, so new growth will take N from older plant parts if it needs to.
And if you look more closely at that wheat crop, you might see that some of those upper leaves are more of a pale green, turning to yellow. “That’s because sulphur affects the formation of chlorophyll,” says Tyler Huber, marketing representative with Nutrien in Saskatoon. That’s key, he says, because without adequate chlorophyll, photosynthesis is compromised, and that can lead to yield losses.
“Not even one-third of wheat acres on the Prairies get S in their fertilizer blends,” says Huber. “The rule of thumb with sulphur in wheat is that it’s the fourth most limiting nutrient. But there is data from reliable sources that indicate you can get a return with sulphur in wheat.”
So are farmers just not paying enough attention to sulphur? Overall, Huber doesn’t think so, if for no other reason than when canola is on a field, which is often, sulphur is in the spotlight. “It’s pretty much a primary nutrient for that crop,” he says.
But he does think that growers could be more aware of what sulphur deficiency looks like in other crops and take steps to ensure that there is enough available sulphur for them to reach full yield potential.
Sulphur 101
Not only do plants need sulphur for chlorophyll production, it’s also essential for protein synthesis, a component of key amino acids, and can even influence structural plant components, which is why smaller leaves and spindly stems can also be a sign of sulphur deficiency.
As Huber points out, while nitrogen is the primary nutrient for growing bushels, it needs sulphur in the sidecar, so to speak, to make sure those bushels happen. And even though plants require less sulphur than nitrogen in general, it does need to be there in sufficient quantity and in a plant-available form throughout the growing season.
Huber says this is where Smart Nutrition™ MAP+MST® from Nutrien makes so much sense for growers looking for a balanced, reliable sulphur supply for their crops.
Smart Nutrition MAP+MST is a homogeneous granular fertilizer that delivers sulphur and phosphate more efficiently and consistently. “One of the things MAP+MST has going for it is that it’s elemental sulphur that’s available to the plant in the year of application and throughout that season,” says Huber.
The first question is how on earth can elemental sulphur be plant-available all season? Huber explains that Smart Nutrition MAP+MST contains micronized elemental S from a patented process called Micronized Sulphur Technology (MST) used under license by Sulvaris Inc.
“We’ve all seen those pictures from the old days where elemental sulphur doesn’t break down, and you can see chunks of it in the soil,” says Huber. “Typical elemental S is upwards of 600 microns while in Smart Nutrition MAP+MST particle sizes average 15 microns, so the oxidation rate is fast and sulphur is available in as little as two weeks from application.”
To make Smart Nutrition MAP+MST, MST is integrated into the mono-ammonium phosphate (MAP) manufacturing process, resulting in granules with consistent percentages of sulphur and phosphate throughout, and high nutrient density. “It’s a highly homogenized product, with 9-43-0-16 all in every granule for very uniform distribution of sulphur,” says Huber. “If you’re already figuring out what to do with MAP and ammonium sulphate, this is a much easier option because it’s all in one.
“It’s also very easy to handle and safe,” he says, adding that the product’s elemental S is not a salt, meaning Smart Nutrition MAP+MST has an extremely low salt index, making it very seed-safe.
How much S do you need?
Soil tests for sulphur levels can be unreliable, for starters. And it’s common knowledge that sandy and light-textured soils are prone to nutrient loss through leaching, while highly productive soils can wind up nutrient-deficient simply because the crops have used it up.
But if you know a field hasn’t had an application of elemental sulphur in a while, or if you farm in an area where cool conditions can persist well into the spring, such as in some of the more northern regions, Huber suggests building sulphur levels in a layered approach.
“We recommend 25 per cent of your S as ammonium sulphate along with the Smart Nutrition MAP+MST in the first year,” he says, explaining that the short-term availability of the former gives the latter enough time to oxidize and become plant-available for the rest of the season.
Huber says current high commodity prices mean growers are more willing to take a closer look at sulphur in their fertilizer blends — obviously on canola, but also on cereals, corn and other non-canola crops.
“Pound for pound, we’re very competitive, price-wise,” he says, adding that it’s not just a price per tonne comparison. “The nutrient density and homogeneity of Smart Nutrition MAP+MST means less hauling and farmers can cover more acres per tonne than MAP only. I’m seeing a lot more growers using more sulphur across the Prairies.”
