Better Sulfur Timing for Crops

By Scout Nelson

Daniel Kaiser, a University of Minnesota Extension nutrient management specialist, explains that sulfate, the plant-available form of sulfur, does not disappear from soil as quickly as many people believe. While sulfate can leach because of its negative charge, research shows that the rate of loss depends greatly on soil type. Medium and fine-textured soils often hold sulfur longer than expected, while sandy soils lose nutrients more quickly.

Current research projects in Minnesota study how sulfur carries over from year to year. In a long-term trial funded by agricultural research groups, sulfur was applied for four years in continuous corn. After that period, some plots continued to receive sulfur while others stopped. Application rates included 5, 10, and 20 pounds of sulfur per acre using both sulfate and elemental sources.

Results from research sites at Rosemount and Waseca show that applying 10 pounds of sulfate per acre for four years allowed sulfur to carry over for at least two additional years. This carryover was enough to meet corn sulfur needs during that time. Lower application rates showed slight yield loss when sulfur applications stopped, suggesting crops still required minimum sulfur levels.

The findings help explain why some earlier research sites showed limited crop response to sulfur fertilizer. In many cases, farmers had already applied sulfur in previous seasons, leaving enough residual sulfur in the soil to support crops.

Soybeans also require sulfur, but research shows that direct sulfur application to soybean fields rarely increases yield. Across about 30 trials over 18 years, only two showed clear yield benefits. Instead, sulfur applied ahead of corn in a corn-soybean rotation often benefits both crops. Studies show that 20 pounds of sulfur per acre can support corn and later improve soybean performance through carryover effects.

Kaiser also discusses timing and fertilizer sources. Corn, alfalfa, and canola respond strongly to sulfur applications. Fall applications may work on certain soils, but fertilizer type matters. Elemental sulfur products, especially sulfur-bentonite blends, may take years to become fully available if incorporated too quickly. Delaying incorporation or adding sulfate sources can improve results.

Overall, research shows that sulfur management depends on understanding soil type, fertilizer source, and timing. With proper planning, growers can improve crop performance while reducing the risk of nutrient deficiency.

Photo Credit: gettyimages-eugenesergeev