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Here’s what you should know about potential products and rates.

Tom J. Bechman, Editor, Indiana Prairie Farmer

February 23, 2024

3 Min Read
A soybean field of varying colored green rows
SEEING IS BELIEVING: Extension soybean specialist Shaun Casteel believes this photo of the Purdue sulfur trial from Aug. 30 says it all. These plots were planted April 18. The shorter, untreated check is on the left. Twenty pounds of sulfur per acre was applied on the greener strips before planting. Shaun Casteel

The trend Shaun Casteel observed in sulfur trials from 2018 to 2022 on heavy, Drummer soil near West Lafayette, Ind., pointed toward a significant response for applying sulfur before early-planted soybeans. Due to weather constraints, “early” planting in all those years was early May. What if he could plant in April?

The Purdue Extension soybean specialist found out in 2023. The first planting was April 18. “We had yield differences over 20 bushels per acre for 20 pounds of sulfur per acre applied before planting versus no sulfur,” Casteel says. “The visual effect by late summer was amazing — sulfur plots were taller and greener.”

Yield advantage for the May 12 planting for sulfur vs. the control was about 10 to 14 bushels per acre, more like what Casteel had observed previously. For the June 7 planting, as before, yield advantage was not significantly higher than the control.

Keep reading to see products and rates. “We applied near planting, and that can mean an extra trip,” he says. “If you apply up to six weeks before planting, consider rates of 20 to 25 pounds per acre in case of loss due to leaching.”

Why early planting response?

Casteel suggests that the significant yield response to sulfur ahead of early-planted soybeans is tied to less sulfur available in the soil early in the spring. It’s all about how much sulfur can mineralize in the soil and be available for plant use.

“Less sulfur is mineralized when soil temperatures are cooler,” Casteel says. “As soils warm up, more sulfur mineralizes and is available. That’s why sulfur applied ahead of planting soybeans in June has little to no benefit in yield.”

Plus, in no-till situations, sulfur can be tied up in soybean stubble, and even more so in corn stover early in the season. Breakdown and release occurs as temperatures warm up.

“Sulfur aids nodulation, and some effects may carry through into the reproductive phase,” Casteel concludes. “Our work so far indicates it is crucial to have ample sulfur available when soybeans emerge.”

Sulfur products, rates in early planting trials

The objective since 2018 in sulfur trials with soybeans at West Lafayette, Ind., was to apply 20 pounds per acre for plots receiving sulfur. No sulfur was applied on control plots.

The products compared in the 2023 trial were ammonium sulfate; ammonium thiosulfate; calcium sulfate, which is pelletized gypsum; and pelletized gypsum plus urea. In each case, application delivered 20 pounds of actual sulfur per acre.

How much actual product did it take to apply 20 pounds of sulfur? Casteel notes that application rates were 83 pounds of ammonium sulfate, 6.9 gallons of ammonium thiosulfate, 117 pounds of pelletized gypsum, and 117 pounds of pelletized gypsum plus 87 pounds of urea for the fourth treatment.

He opted for pelletized gypsum because it handles and blends more easily. If using regular bulk gypsum, it would require 500 to 1,000 pounds or more to get enough product to flow and apply evenly, supplying at least 20 pounds of sulfur, Casteel says.

No significant differences in yield were attributed to nitrogen in these trials.

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About the Author(s)

Tom J. Bechman

Editor, Indiana Prairie Farmer, Farm Progress

Tom J. Bechman is editor of Indiana Prairie Farmer. He joined Farm Progress in 1981 as a field editor, first writing stories to help farmers adjust to a difficult harvest after a tough weather year. His goal today is the same — writing stories that help farmers adjust to a changing environment in a profitable manner.

Bechman knows about Indiana agriculture because he grew up on a small dairy farm and worked with young farmers as a vocational agriculture teacher and FFA advisor before joining Farm Progress. He works closely with Purdue University specialists, Indiana Farm Bureau and commodity groups to cover cutting-edge issues affecting farmers. He specializes in writing crop stories with a focus on obtaining the highest and most economical yields possible.

Tom and his wife, Carla, have four children: Allison, Ashley, Daniel and Kayla, plus eight grandchildren. They raise produce for the food pantry and house 4-H animals for the grandkids on their small acreage near Franklin, Ind.

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