[UPDATED: Oct. 10, 2019] When you consider the cost and bulkiness of conventional sulphur fertilizers, producers can hardly be blamed for seeking out alternatives to meet their crops’ sulphate needs.
One of these alternatives is elemental sulphur — a byproduct of the oil and gas industry that is plentiful and cheap in Western Canada.
But should you use it?
Over the past seven years, a fertilizer product combining elemental sulphur with compost has shone a spotlight on this nutrient.
Produced by Calgary-based Bio-Cycle Solutions, Bio-Sul has proven quite popular, with about four million acres’ worth sold to date.
Elemental sulphur can be a safe and effective source of sulphur for crops, said Doon Pauly, an agronomy research scientist with Alberta Agriculture, the province with the most experience with its use.
But using it requires a rethink of fertilizer management practices due to the extended time it takes to become useful. That’s why elemental sulphur fertilizers are generally applied, usually by spreading, in the fall.
“Elemental sulphur needs to fit into a longer-term management process,” said Pauly. “You can’t put it on for immediate crop needs; you apply it for a long-term sulphur level in the soil.”
Bio-Sul does require long-term thinking, it’s different from other elemental sulphur fertilizers on the market, said Neil Wiens, who developed the product.
According to Wiens, it tackles some of the biggest challenges of elemental sulphur, including high salt content and particle size. The compost itself accelerates translation to sulphate, kills diseases and reduces dusting and fire risks.
“It emerges very rapidly in the soil once it hits the soil in the right conditions,” said Wiens.
(Particle) size matters
When most people talk about conventional sulphate fertilizer, they’re usually referring to ammonium sulphate. For all of its arguable inefficiencies, the advantage of ammonium sulphate is that it’s already in the form required to facilitate crop growth. By contrast, it takes time for micro-organisms in the soil to oxidize elemental sulphur (the process which turns it into sulphate).
The efficiency of the oxidization process depends largely on the particle size of the elemental sulphur.
That means not all elemental sulphur products are created equal, said Pauly.
“For that oxidization to happen the sulphur has to be in contact with the soil organisms and as close as possible to their size,” he said. “We are talking about organisms that are a thousandth of a millimetre in size. So if you put on golf ball-sized chunks of sulphur the chances of that being oxidized are pretty close to zero.”
So how small do these sulphate particles have to be?
About 30 years ago renowned soil scientist Henry Janzen suggested they should be under 100 microns in size.
“That’s still huge compared to the organisms but you’re talking about something that is a fraction of a millimetre in size.”
There are dangers in elemental sulphur in its raw form. It’s dusty, which creates an environmental and safety risk due to the explosive nature of sulphur.
This is why most commercial elemental sulphur fertilizers are mixed with bentonite, which reduces dust and allows elemental sulphur to take on water, expand and disintegrate. Spreading and other physical agitation brings the particles closer to the size required for oxidization.
The difficulty with bentonite-amended elemental sulphur is that it’s hard to determine when the sulphate will be available to the crop. Again, this calls for long-term management, said Pauly. “You can’t predict it. You need to apply it for a long-term sulphur level in the soil.”
That term shouldn’t be any more than three years due to the high salt content of sulphur, said Pauly.
“I don’t like seeing it applied at any rate higher than a crop will remove over three years. If the crop is removing 20 pounds a year then I don’t like seeing any more than 60 pounds of sulphur applied,” he said.
“Sulphur is very mobile. Depending on rainfall, slope and other factors in the field, it can move from its place of application and end up in a lower spot on the landscape or move with groundwater off the field.
The compost factor
Bio-Sul is comprised of 70 per cent elemental sulphur and 30 per cent compost — mostly from food waste. Wiens said Bio-Sul has been created as a safer, more cost-efficient alternative to commercial sulphur fertilizer.
It also comes with the added social benefit of repurposing food waste. Bio-Cycle Solutions collects up to 32 tonnes of waste per day from grocery stores, restaurants and malls. This is composted and amended with elemental sulphur to create a nutrient-rich compost base. Its low salt index helps reduce the salinity risks associated with other elemental sulphur products.
The big advantage of Bio-Sul over ammonium sulphate fertilizer is price, said Wiens.
“When you factor out the cost of nitrogen out of ammonium sulphate, you’re looking at – depending on the time of year — an average of around 40 cents per pound of sulphur. We tested at about 20 cents per pound of sulphur.
“It’s a product that helps you logistically. Being able to take ammonium sulphate out of your tank increases your efficiency in the field by about 25 to 30 per cent because you don’t have to stop every 60 acres to refill.”
Bio-Sul is composed of a range of elemental sulphur particle sizes from 10 to 2,000 microns. The company claims this variety of sizes provides an extended breakdown period starting with the smallest particles, which are available to the crop within the first 12 months.
Microbes required to convert sulphur to sulphate are already present in the compost, kick-starting the oxidization process. Compost also eliminates the need for bentonite because it reduces dust and the risk of fire, said Wiens.
The product requires an initial application of about 200 pounds per acre with availability averaging between four and five years.
Although some producers have expressed concern over putting waste product into their soil, composting and the basic nature of elemental sulphur help eliminate crop diseases such as clubroot as well as salmonella and E. coli, said Wiens.
“Disease is tested for all the time. Basically, the composting process kills all those uglies. Even if they were to get through — which they don’t — the wonderful thing with elemental sulphur is that nothing lives in it. Any bugs that would be a problem would get absolutely nuked.”
UPDATE: The article previously incorrectly stated that Bio-Sul was comprised of 30 per cent sulphur and 70 per cent compost.
This article originally appeared on the Alberta Farmer Express.