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Sulphur gets hot

The nutrient’s use is definitely trending up, and there’s still more room for growth

It’s a question that’s asked of a lot of nutrients in soils across Eastern Can­ada: Is there enough in my soil, or isn’t there?

Discussions surrounding deficiencies and field levels typically target macronutrients like potash and phosphorus, or even other nutrients like nitrogen, or the micronutrients magnesium, manganese, boron, zinc or copper.

But sulphur sits in its own space between the well-known macros and micros.

A few years ago, some advisers and researchers were starting to worry, telling growers that sulphur deficiency was showing up in certain crops in Eastern Canada. It was a remarkable development, caused at least partly by the clean-up of air quality and a considerable reduction in atmospheric sulphur deposition.

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The new equilibrium was leaving crops across much of Ontario and into Quebec showing symptoms of sulphur deficiency.

The reason for this concern has to do with sulphur’s role not only in the formation of amino acids and proteins but in the production of chlorophyll too, not to mention that sulphur also helps with nodulation and it develops and activates certain vitamins and enzymes.

Still, there is no reliable S soil test, which means it can only be realistically monitored by watching for symptoms, such as pale upper leaves and interveinal yellowing.

The trouble is, those symptoms can also be caused by rapid growth or by deficiencies in other nutrients such as manganese, magnesium or zinc. (Tissue sampling will help sort out the confusion.)

Crop advisers, extension personnel and university researchers tend to agree that more research is needed on sulphur in almost all crops. The exceptions might be alfalfa, canola and to a lesser extent, cereals — growers with those crops have generally recognized its vital role there.

Less is known about sulphur on corn and soybeans, except to say that there are plenty of options for growers when it comes to applying sulphur to those crops.

Nutrient partnership

The relationship between sulphur and corn appears to be the simplest. Canola has been a long-term beneficiary of sulphur applications, and cereals and forages have become a little more automatic in their reliance on the nutrient. Yet corn has a fit with nitrogen applications and sulphur works well with nitrogen, functioning at roughly a 10:1 ratio.

A grower applying 70 or 80 lbs. of N per acre can add in seven or eight lbs. of S per acre as cheap insurance. According to figures from the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), a 185 bu./ac. corn crop will take as much as 27 lbs. of S per acre per year while removing 15 lbs. per acre.

“In Eastern Ontario, corn has had the most sulphur of any crops for quite some time, just because it was getting nitrogen already,” says Paul Sullivan, of Sullivan Agro near Kinburn, Ont. “Phosphorus sources are being used that contain S and there’s an associated thought process of nitrogen and sulphur needing to go together for corn. Recently, alfalfa has seen more usage and there have been people in the fertilizer industry who have been using it on their hay fields and in wheat, but it wasn’t necessarily recognized there was a need for it until recently.”

Some fertilizer products — like MES/MESZ, which is nitrogen, phosphorus, sulphur and zinc combined — have been applied to corn for much of the past decade. In his fertilizer recommendations, Sullivan has used sulphur on corn the longest, then hay followed by cereals.

In spite of that familiarity, there is still a reluctance to apply some forms of sulphur to some crops. Growers are either skeptical about its impact or they have opted out of it. Sullivan maintains that once they see the effect for themselves, it’s an easy sell to get them back on track.

Seven years ago, Sullivan noted that sulphur deficiency in corn showed up in his area on some lighter ground. In 2012, they had some winter wheat that they were just starting to work with and they tested sulphur. And where they didn’t put it on, they saw the difference. Some plots were sprayed with ammonium thiosulphate, which helped “rescue” some of the fields. Since then, it’s applied in the first broadcast in the spring on all cereal acres.

“There was a field that we had put some ammonium sulphate on, broadcast it on, and there was an area where they stopped the spreader, and it was like night and day,” Sullivan says. “It was on lighter ground where we saw most of the difference that year.”

The other scenario where sulphur is important is with corn-on-corn crop plans. In those cases, Sullivan can get a bit of a tie-up with sulphur and having it in the fertilizer blend to be cycling and available to the crop is vital.

“It’s not necessarily new but the more we see of its usage, there isn’t a lot of information that would suggest that there’s a big response on corn on heavier soils,” says Sullivan. “Or there’s the potential that’s there, even though on the lighter sands there has been a definite visual response in the spring, whether a grower uses sulphur or doesn’t use sulphur. But it becomes more over the course of the season when sulphur is important to corn — later in the season and sometimes you can get it made up by some added sulphur that mineralizes out.”

Sullivan cites another example of a planter trial in his region earlier this spring. A local dealership was demonstrating a new planter with liquid starter on it (with 6-24-6 and zinc), and planted in a client’s field that had dry fertilizer and a sulphur source with the starter. This deviated from the original fertilizer plan for the field so the S wasn’t applied. The corn that was planted with the liquid starter had visible striping on the leaves and a tissue sample revealed that it was sulphur-deficient, though within the week of that showing up, the corn grew out of it.

“It can look very different early on with a lot of things in corn yet never really amount to significant bushels,” Sullivan says. “But even if you’re getting three to five bushels of corn, that’s definitely paying for the sulphur. The mentality with corn is that ‘we don’t want to short it on anything,’ so we just make sure we throw everything at it.”

Different region, same basic demands

As different as cropping practices, soil types and crop heat unit regions might be in Eastern Ontario compared to southwestern parts of the province, the story on sulphur is much the same. It’s an accepted nutrient for forages, corn — and even soybeans — but more research is needed to benchmark the levels.

“It’s been somewhat the forgotten nutrient because we’ve relied on mineralization and atmospheric deposition mainly, but growers understand it’s an important nutrient,” says Ryan Ben­jamins of Benjamins Agronomy Services, in Plympton-Wyoming, Ont., “especially the effect on chlorophyll, where sulphur is a nutrient that when it’s deficient, it’s very visual. By adding sulphur, you go from a pale-looking crop to a deeper green, almost blue in colour.”

Again, since there is no soil test component for sulphur, verifying its place in cropping practices can be a challenge, beyond “the way the crop looks.” That’s why Benjamins advocates for growers to conduct their own on-farm plot tests, knowing they may be surprised by their own “unintentional use” of sulphur in corn.

“Any producer who’s in a dry fertilizer, two-by-two system or maybe a strip-till placement, if they’re using ammonium sulphate for nitrogen, MESZ for phosphorous and zinc or K-Mag for magnesium, they may be adding sulphur unintentionally,” says Benjamins. “There are a lot of products out there that contain sulphur as a bonus.”

It’s something that he’s been seeing in farm trials where he’s testing for sulphur. Growers want to see some response to sulphur but it comes as a surprise when they realize they’ve been using it for some time. And that’s Benjamins’s recommendation to producers in terms of cost: to use a product like K-Mag or MESZ that would give them the beneficial impact of added sulphur. If growers are in a liquid fertilizer system, ammonium thiosulphate (or similar products with sulphate S) makes it convenient to blend in and save on application costs.

This article was originally published in the Sept. 2018 issue of the Corn Guide.

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