Sulfur has been an essential part of Perry Goetsch’s alfalfa management plan for nearly 15 years. “Using sulfur,” says the Ixonia, WI, dairyman, “is the key to unlocking alfalfa yields. I strictly believe that.”

Until three years ago, he applied elemental sulfur, which needs months of time, warm temperatures and a bit of moisture for bacteria to turn it to the plant-usable sulfate form.

But Kyle Stull, a certified crops specialist with Frontier-Servco FS, convinced Goetsch to switch to ammonium sulfate, which gives sulfur-deficient alfalfa an immediate boost.

“He’s getting pretty much incredible yields as far as the county average is concerned,” Stull says of the 120 acres of alfalfa Goetsch grows. “He’s getting to the point where he has to cut back on hay acres because he’s getting too much hay.”

“Every year we grow less alfalfa and have more feed,” Goetsch agrees.

In 2011, the county average was 3.3 tons dry alfalfa; in 2012 it was 2.3 tons in the drought, Stull says. “Perry had 6.4 tons/acre dry last year and close to 9 tons in 2011.”

Applying sulfur in a sulfate form, whether as ammonium sulfate (AMS), potassium sulfate or calcium sulfate, does give alfalfa a yield bump – provided the crop needs sulfur. That’s according to Carrie Laboski, soil fertility and nutrient management specialist with University of Wisconsin Extension.

“We’ve seen yield increases where you apply the sulfate form – because it’s immediately available and it’s a sulfur-deficient crop – of 1 ton/acre over the whole growing season. That’s going to more than pay for that sulfur application, because sulfur might cost $25-30/acre and a ton of hay is probably $150 or better right now,” she says.

But elemental sulfur, which is 90% sulfur, also serves a purpose, Laboski says. “Because it’s a slower-release material, it has some longevity” in the soil.

She is researching the possibility of applying the elemental and sulfate forms of sulfur to alfalfa together to get immediate and long-term benefits with one application. “We’re still a year or two from being able to provide growers sound guidance on this practice.”

A big clue that an alfalfa field needs sulfur: lighter-green or yellowish patches, Laboski says (see left). Until recent years, those patches showed up after first cutting. Now some fields are showing lighter patches at green-up

Rather than soil test to find out if a field needs sulfur – soil tests can’t pinpoint sulfur levels as well as they do for potassium and phosphorus – Laboski recommends tissue testing.

“Just prior to first cutting at the bud to first flower stage, take about 20-30 stems, and just the top 6” of the stem, and send that to a lab,” she says. If the results show that plants have less than 0.25% sulfur, it’s deficient.

“The lower the number, the more deficient. So if you’re at 0.24%, you might see a little bit of a yield increase from applying sulfur, but it’s not going to be huge. If it’s at 0.15%, that’s when you’re going to see bigger yield increases.”

Before growers decide what form of sulfur to apply, they should look at a field’s total nutrient needs. “To make a very broad statement, at least in Wisconsin, there’s probably not a hayfield out there that doesn’t need potash,” Laboski says.

She thinks growers should consider applying potassium sulfate, which contains 50% potassium and 18% sulfur, rather than AMS, made up of 21% nitrogen (N) and 24% sulfur. Alfalfa, which fixes its own N, doesn’t need the N it gets from AMS. Potassium sulfate, however, provides two needed nutrients.

“But it’s expensive,” she says. “People get sticker shock. This spring I did a little survey and potassium sulfate was $807/ton. Ammonium sulfate was, by contrast, $459/ton.

“So they look at that and automatically say, ‘AMS is cheaper.’ But, then, they’re not thinking about the amount of nutrients in there.

“For example, a 130-lb/acre rate of potassium sulfate can range in price from $47.45 to $58.18/acre and will supply 23.4 lbs sulfur and 65 lbs potassium per acre. An application of 100 lbs/acre each of AMS and potash will supply 24 lbs sulfur and 60 lbs potassium per acre and will cost $48.25-53.80/acre,” Laboski points out.

“So, for very similar application rates of sulfur and potassium, potassium sulfate may be a more economical source of nutrients compared to AMS and potash. The key is to check prices in your area and do the math.”