Reduction of Sulfer Applications

Clarke McGrath, crop specialist

Sulfur is an essential crop nutrient that is often marketed as a fertility program ingredient by fertilizer dealers to clients in the hope that it will increase yields. ISU data, as well as data from other midwest Land Grant Universities, shows little, if any benefit to the addition of S to a fertilizer program. While the midwest data is useful, growers and dealers both request more "localized" data to base decisions on. With an average cost of around $4 per acre for S fertilization, dealers and growers need unbiased, research based information they feel comfortable with in order to decide whether or not to apply S fertilizer to their crops.

Over the last 4 growing seasons, with the cooperation of several local ag chem dealers, growers and seed companies, I have had a total of at least 17 plots evaluating corn/bean response to S fertilization. All plots have been in a corn/bean rotation, under various tillage systems, including no-till. Results of the research have been shared with clients in southwest Iowa through meetings, publications and email updates.

Although extractable S levels in the 0-6" depth at over 1/2 the sites were lower than the reported 10ppm critical level (Hoeft, et al.), again this year there was no response to the S applications in yields for corn or soybeans. This has held true for every plot, each year, and is consistent with findings from earlier ISU research by state fertility specialists such as Dr.'s Killorn, Mallarino and Sawyer. It appears, for at least the current sites, that the combined S supply from soil profile sulfate, atmospheric deposition, crop residue and organic matter mineralization continues to meet crop requirements.
In an evaluation of this information, several ag chem dealers and growers were asked to share if, and how, they have used this research work to adjust their S fertilizer applications. Results were compiled and indicated that approximately 5,600 acres of crop land that had received regular S applications previously to this research work being shared were no longer having S applications made to them. While this is a small sampling of area clients, for these grower the savings are approximately $22,400. This work will continue with various S sources and application methods.

Page last updated: July 8, 2006
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