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Boost alfalfa yields with sulfur

Without sulfur, plants tend to appear yellow and stunted
Photo courtesy of Michigan State University

Alfalfa needs sulfur to grow. Before the 1990s, the source of sulfur came from acid rain. When environmental regulations kicked in, the sulfur supply began disappearing. This means hay producers now need to add sulfur in their fertilizer application.

Dan Undersander is an Extension forage specialist at the University of Wisconsin. He says alfalfa takes up sulfur as sulfate, converts it into amino acids, and then into proteins.

"Without the sulfur, the plants tend to be stunted and they tend to appear yellow in the field if we have a severe deficiency because they can’t grow and then they’re also not fixing enough nitrogen from the air," says Undersander. "The combination of factors means that sulfur-deficient plants are lower yielding, and they are not as competitive against weeds."

Undersander says the sulfur application rate is about five-pounds-per-ton of dry matter removed. For example, if you’re harvesting six-tons of alfalfa from a field, then you have removed 30-pounds of sulfur. You’ll need to put that back into the soil, plus 10%-15% more.

He recommends applying sulfur twice a year.

"Once after first cutting, and then again in the fall. After first cutting, we could put on 25-30 lbs. of sulfur, and then with the fall application of potassium, we could put on the remainder that we need to have based on the yield that we got during the year."

The most common source of sulfur is in a sulfate form, such as potassium sulfate, ammonium sulfate, or gypsum, which is a calcium sulfate.

Learn more about the benefits of sulfur

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