The other nutrient…sulfur

Written by Jonathan Eisenthal

It became clear to the producers and crop consultants gathered in Rochester to learn the latest about conservation tillage that, since nutrients are critical to the success of any crop, they become even more critical for producers engaging in conservation tillage techniques. A key nutrient that’s gaining more and more attention among researchers in the past few years is sulfur.

Soil scientist Jeff Vetsch devoted an entire talk to sulfur at the 2012 University of Minnesota Conservation Tillage Conference, and sulfur became a very popular item among the “table talk” discussions—a kind of ‘speed-dating’ version of the usual panel discussion format, where the audience has the opportunity to switch to a different table (and topic) every 15 minutes over the course of an hour.

Vetsch told the group that researchers have documented that adding sulfur is profitable between a third and half of the time, and making it a regular practice “pays for itself.” The biggest yield boosts were seen when using sulfur in corn-on-corn rotations that use conservation tillage, and also with fields that have low or variable organic matter or eroded hilltop areas, and also fields with no recent history of sulfur fertilization.

The latest research estimates that optimum rates for fine and medium soils are 10-15 pounds per acre each year when broadcasting, or 5-8 pounds when putting in a band. For sandy soils, they have seen economic returns at a rate of 25 pounds per acre each year. Vetsch notes that sulfate is the form that plants can utilize directly. Elemental sulfur takes a period of time to mineralize and become available to plants, so it can be a good option for fall applications, but is not as effective when it is combined with spring fertilizer passes.

“Sulfur continues to be the surprise fertilizer,” said Brad Carlson, a crops educator with University of Minnesota Extension Service.  “Sulfur was heavily studied in the 60s and 70s, and scientists never could find much response to it then.”

One reason for this change, scientists speculate, is the major drop in atmospheric sulfur that has followed the reformulation of fuels in order to prevent acid rain. Measurements in 1986 recorded averages between 12 to 15 pounds of sulfur deposited from atmosphere, compared to between three and four pounds in 2005, according to Vetsch, and southern Minnesota sees even less than that with an average estimated atmospheric deposition of 1.5 pounds of sulfur.

“Even now we want to recommend using sulfur where you have low organic matter, but we are seeing yield responses to sulfur all over, everywhere, in all kinds of crops,” said Carlson.” Sulfur remains a bit of a mystery. We don’t have a reliable test, in that you can get back a test result that recommends no need for additional sulfur fertilizer and yet if you go ahead and add it you get a response. The story is not yet written. There’s an assumption that if we apply sulfur at a fairly high rate we won’t see a response, but we haven’t found that limit yet.”

Vetsch was asked if an over-application of sulfur would build up the helpful nutrient in the topsoil, and he responded that “it is an ion, it becomes mobile so there is no banking (for sulfur).”

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