The Indiana Certified Crop Adviser panel includes Danny Greene, Greene Crop Consulting, Franklin; Brian Overstreet, soil conservation coordinator, Rensselaer; and Dan Ritter, Hoegemeyer Hybrids, Rensselaer.

 

I’ve heard that fall applications of sulfur can boost soybean yields the following season. We farm heavy clay soils, and with spring logistics and labor constraints, it’s a challenge for us to make sulfur applications prior to planting. Should we apply sulfur this fall? If so, at what rates?

 

Greene: Sulfur can boost soybean yields in responsive situations. Source and timing are important. Plants take up sulfur primarily as sulfate. Since sulfate is negatively charged like the nitrate form of nitrogen, it doesn’t bind strongly to soil particles and can leach, particularly in soils that experience considerable water movement.

 

Therefore, I’d be cautious about relying on a fall sulfate application for the next year’s soybean crop. Applications close to planting or during the growing season reduce the risk of sulfate moving out of the root zone before the crop needs it.

 

Elemental sulfur is a better option for fall application. It isn’t immediately available to the plant and must first be converted by soil microorganisms to sulfate. That process takes time and is affected by soil temperature and pH.

 

Applying around 15 to 25 pounds of sulfur per acre is a reasonable rate to evaluate, although expect responses to vary with soil type, sulfur source, timing and environmental conditions. For instance, in your situation, higher rates than this may be needed in the fall to support next season’s soybeans.

 

Cover crops may also capture some fall-applied sulfur and recycle it as residue decomposes. With cover crops, a sulfate sulfur source like ammonium sulfate could be a good solution. Given your heavy clay soils and spring workload, I wouldn’t rule out a fall sulfur program, and I would recommend elemental sulfur. But test different rates to determine a rate that meets your goals.

 

Overstreet: The preferred sulfur application timing would be in the spring because of the mobility of sulfur. If you are locked into the fall, the only form of sulfur I would use is elemental sulfur. It takes time to break down to become water soluble and available for the plants to use in the spring. Apply at rates of 15 to 20 pounds per acre blended in with your potash and phosphorus.