Secondary Doesn't Mean Second Place

fertilizer and nutrient word cloud

Sulfur (S) is a secondary nutrient, not because it is of lesser importance to corn, soybean, or alfalfa plants, but because plants use sulfur in smaller quantities than they use the primary (macro) nutrients of N, P, and K.

Sulfur is a part of every cell in the plant. Brad Hipsag, agronomy sales rep at Federated’s Ogilvie location, noted that “S is key for plant protein, seed production, and nodulation of legume plants” (such as soybeans and alfalfa).

It’s important not to overlook sulfur needs.

  • 200-bu. corn can use 16 lbs. of S in the grain;
  • 50-bu. soybeans can take up to 10 lbs. of S during the growing season;
  • 6-ton alfalfa can use 32 lbs. of S at its peak.

Sulfur needs to be added annually.

Federated recommends ammonium sulfate (AMS) as part of an effective crop management program. “AMS is one of the most soluble and most plant-available forms of sulfur fertilizer,” said Hipstag.

AMS is 21% N in the ammonium form and 24% S in the sulfate form (21-0-0-24), which means every 100 lbs. of AMS delivers 21 lbs. of N and 24 lbs. of S. Because AMS is leachable (sulfur in the sulfate form is mobile in the soil), it should be managed similarly to N. It is especially important to well manage S in low organic, sandy soils.

Hipsag said he prefers to “split-apply the AMS on corn – half upfront as a pre-plant broadcast or in the row as starter, and half top-dressed with the remaining nitrogen.” Federated Agronomy Manager Kevin Carlson noted another reason for split applying sulfur in corn: It needs a steady supply well past flowering/tassel because only about 50% of the crop’s needs have been taken up by that point. Also, since sulfur is immobile in the plant, a steady, reliable and available form of S needs to be in the root zone through the growing season. AMS provides that sulfate form (SO4).

While Federated highly recommends AMS, growers do have other S alternatives, including elemental sulfur and gypsum applications. In any case, don’t overlook S.

For years people have said nitrogen in corn needs to be managed as if profits depended on it. It could be argued that the same now applies to sulfur.

Discuss specific sulfur and nutrient management needs with your local Federated Agronomist to determine the best option.