We want to apply sulfur ahead of soybeans to boost yields. When should we apply? What product? What rate?

The Indiana certified crop advisers panel answering this question includes Andy Like, independent crops consultant, Vincennes; Jeff Nagel, agronomist with Ceres Solutions, Lafayette; and Marty Park, agronomist with Gutwein Seed Services, Rensselaer.

Like: Typically, sulfur is applied to soybeans before planting to minimize tire damage. However, sulfur in a liquid form can be applied at planting or with a sprayer prior to emergence. The most common forms of sulfur in our area are:

Choice of product will depend on availability of products and application equipment. Target 15 to 25 pounds of sulfur per acre for a test. Sulfur is applied most often as ammonium sulfate with a dry spreader prior to crop emergence in combination with phosphorus and potassium fertilizer.

Nagel: Shaun Casteel, Purdue Extension soybean specialist, conducted multiyear research on sulfur response in soybeans. This is ongoing research, and they learn new things each year. The probability of response to sulfur in soybeans increases with earlier planting dates on timber soils and is more consistent on sandier soils.

Soluble sources that provide plant-available sulfate-sulfur are needed. This could be ammonium sulfate (AMS), ammonium thiosulfate (ATS), pelletized gypsum and some others. Typically, AMS or ATS are more widely available. What source you use needs to fit into your farming system.

Here are some guidelines based on our experiences with sulfur in soybeans:

Park: The most common practice in the area that I service is applying dry ammonium sulfate at 50 to 100 pounds per acre in the spring. Ideally, it is applied no more than 30 days prior to planting. Quite often, it is applied with other dry fertilizers. There are other newer product combinations, like elemental sulfur and sulfate-sulfur, that could be considered. Remember that elemental sulfur is not immediately available.