Essential Sulfur
More growers are realizing there’s a sulfur shortage in the soil and that the macronutrient is crucial for crop growth and development
It has been more than 50 years since the signing of the Clean Air Act, which Nutrien’s Dr. Karl Wyant hails as a tremendous achievement for America’s environment and economy.
“The Clean Air Act’s success can’t be understated,” says Wyant, Ph.D., the Director of Agronomy for Nutrien, the world’s largest provider of crop inputs and agricultural services and solutions.
In the mid-20th century, with the economy growing and the country’s manufacturing sector expanding, an unintended consequence was air pollution. But the Clean Air Act has achieved what it was created to do — protect the public’s health and welfare nationwide — and not at the economy’s expense. In fact, the economy has grown thanks to new innovations that have led to cleaner technologies.
“The Clean Air Act has reduced the aggregate emissions of the six most common air pollutants by 74% compared to the 1970 baseline,” Wyant says, noting that during that same time the U.S.’s gross domestic product (GDP) has grown by 275%, its population by 60%, and its energy consumption by 50%.
“The decoupling of the traditional lockstep trend of energy consumption, air pollution, and GDP growth has been a big win for the U.S.,” Wyant adds.
One of the six pollutants the Clean Air Act has removed from the air is sulfur dioxide, which is produced from the burning of fossil fuels and industrial processes to make energy. As a result, the amount of sulfur deposited in the soil in the form of acid rain and through atmospheric deposition has steadily declined over the last several decades.
While Wyant reaffirms that removing sulfur and other pollutants from the air has improved public and environmental health, among other things, the removal’s long-term impact has caused a challenge for growers: a sulfur shortage during the growing season.
“The sulfur levels in the soil and crop tissues didn’t go from high to low overnight,” Wyant says. “There has been a gradual reduction over time, and we are seeing increased reports of sulfur deficiencies as a result.”
Plants Need Sulfur
The days of free sulfur literally raining down from the sky into the soil are over.
“That was sort of a weird, good thing that growers took advantage of, didn’t have to pay for, and didn’t have to manage,” Wyant says of the free sulfur. “But the steps taken to clean up air pollution have resulted in a lot less free fertilizer coming down from deposition.”
But over time, more growers have realized there’s a sulfur shortage during the growing season and, as The Sulphur Institute states, that sulfur is “essential for the growth and development of all crops, without exception.”
It wasn’t until post 1990 when pollution controls intensified did growers begin seeing the effects of a sulfur deficiency in their crops — a yellowing of younger leaves higher up on the plant — but were unsure about treatment options, Wyant says. It was only when they conducted soil and tissue tests that they learned what was causing the yellowing – sulfur deficiency.
But that learning has created awareness, Wyant says. In the past 10 years, the level of education, training, and awareness among agricultural professionals about the significant role that sulfur should play in crop nutrient management has intensified.
“More growers are recognizing the value in making that sulfur investment,” he adds.
Growers are also realizing sulfur is the fourth most important macronutrient behind nitrogen, potassium, and phosphorus. Education about sulfur’s importance in crops has gained “great momentum,” Wyant says.
Third-party research is also helping. On sulfur-responsive large-plot strip trials conducted at several locations from 2017-2022, Purdue University’s Department of Agronomy found that the average yield increase on an acre from sulfur fertilization ranged from 3 to 34 bushels of corn, with an average of 11 bushels.
Wyant points out that sulfur’s importance as a crop nutrient is also supported by the American Society of Agronomy (ASA), agricultural extension services, and certified crop advisors.
Understanding How Sulfur Works
Wyant says it has been educational for growers to “experience” a sulfur deficiency in crops, from seeing yellowing in crops to understanding why it occurred, and then learning how to treat it and improve yields.
“That personal experience can drive a lot of action in the field,” he adds. “It goes a long way in recognizing sulfur as something growers could put on the back burner, but now place front and center.”
It’s also important for growers to understand how sulfur functions in the soil, Wyant stresses. For instance, if a grower decides to apply 20 pounds of sulfur per acre, the grower needs to decide on the formulation to use. “This determines when you put it out and how you put it out,” Wyant says, stressing that plants can only access sulfur when it’s in its sulfate form (S042-).
Sulfur can be applied in its sulfate form, which makes it available for the plant to uptake immediately. When in this form, it’s important to apply sulfate when the plant needs it, like in the spring when the crop is actively growing, Wyant stresses.
“The challenge with the sulfate form is that it’s highly leachable,” Wyant explains. “Just like nitrogen in its nitrate form, sulfate can go right through the soil.”
Growers can also apply sulfur in its elemental form, which is immobile and resists leaching. But elemental sulfur needs microbes to oxidize it to sulfate, a process that can take time, Wyant states. If applied in the fall when the soil is cool or cold, elemental sulfur will stay in the soil until spring when the soil warms, and the microbes oxidize it for when the plant needs it.
Depending on what growers are trying to get done in the field and how immediately they need to solve a problem is how they will make the choice between using sulfate sulfur or sulfur in its elemental form, Wyant says. “It’s about matching the tool to the job,” he adds.
One tool growers should consider is Nutrien’s Smart Nutrition™ MAP + MST (9-43-0-16S), which contains a large amount of elemental sulfur in a patented micronized form. The small particle size allows for quicker elemental sulfur oxidation and increased surface area. Smart Nutrition also contains phosphorus.
Overall, thanks to sulfur, growers are now seeing positive yield gains on corn, soybeans, pumpkins, and other crops, Wyant says.
“Sulfur is another tool in the toolbox to help growers stay profitable,” he adds.
For more information on sulfur, please review Nutrien’s free sulfur toolbox: https://nutrien-ekonomics.com/agronomics/toolkits/sulfur/