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Fertilize with sulfur selectively

12/14/2010 @ 11:24am

Sulfur fertilizer offers no yield or protein benefits to spring wheat grown in heavy soils with high organic matter, according to a recent study done by the University of Minnesota (U of M).

“For a producer in the Red River Valley, sulfur (S) applications should not be a high priority for spring wheat,” says Russ Severson, U of M regional Extension educator.

In 2008 and 2009, researchers evaluated the results of applying two types of sulfur fertilizers to spring wheat fields located in the northwestern and southeastern regions of Minnesota.

“When selecting sites for the trials, we did not purposely go to areas that were known to be deficient in sulfur,” says Severson. “We focused rather on soils in the regions where most of the wheat is grown.”

One question driving the study centers on yield increases in the wheat-growing regions with high-quality soil. “We wondered whether the sulfur fertilizer recommendations developed for a 40-bushel (per acre) wheat yield were still adequate for the 90-bushel yields actually being produced,” says Severson.

Researchers wondered, too, if sulfur deficiencies could be contributing to the low protein content in these bumper wheat crops.

Yet a third reason for doing the study relates to decreases in the amount of sulfur deposited through rainfall as acid rain. “With the scrubbing of sulfur from smokestack exhaust, we’re getting less sulfur from acid rain,” says Severson. “We wondered whether or not this could be making a difference in wheat yields.”

The two sulfur fertilizers they studied were spring-incorporated ammonium sulfate and the brand name fertilizer MicroEssentials MES15. Ammonium sulfate was also applied as a tillering treatment in season to both the ammonium sulfate and MES sulfur fertilizer treatments.

In the brand name product, one half of the sulfur is immediately available as ammonium sulfate. The other half is in the elemental form of sulfur that must be mineralized by soil bacteria in order to become available to plants later in the growing season.

The straight ammonium sulfate was applied at amounts supplying 12.5 pounds per acre of sulfur, 25 pounds per acre, and 37.5 pounds per acre, as was the brand name product. The tillering in-season application was ammonium sulfate only applied at 0, 12.5, and 25 pounds per acre. Unfertilized plots were control sites. Glenn was the wheat variety grown in all plots.

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