Sulfate Over Winter

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Beneficial Reuse Management LLC

Gypsum is a ready-made sulfur source for crops, explains Ron Chamberlain, GYPSOIL's chief agronomist and founder.  "It goes onto the field with sulfur already in the sulfate form,” he says.  Elemental sulfur, on the other hand, requires oxidization by soil bacteria to SO4 or sulfate before it is available. This process also produces acid and drives down the pH.

But what happens to the sulfate over the winter after fall applications of gypsum? Research and practical experience point to strong evidence for gypsum’s staying power.

Researchers at The Ohio State University’s School of Environment & Natural Resources demonstrated in a 2006 study that the sulfate in gypsum remains available in the upper soil profile six months after the last application.1 Other studies provide additional evidence, including an older study in North Carolina documenting the presence of sulfate-sulfur in a silty clay loam soil 200 days after application.2

“We have noticed nice increases in sulfate levels where we apply gypsum, and those levels are holding at 3x to 4x increases 2 to 4 years after application,” says Joe Nester, a crop consultant and owner of Nester Ag, Bryan, OH.

 Gypsum doesn’t dissolve all at once, notes Chamberlain. Factors including the source, particle size distribution and the environment surrounding the material once it is applied, all play a role.

“In soils that are common in the Midwest – silt, clay and loam types  -- the movement of gypsum down through the profile tends to be slower than for sandier soils that are not as common,” Chamberlain says.

With lower commodity prices, one of the big enticements for using gypsum as a sulfur source is cost. Pound by pound, gypsum supplies sulfur at a lower cost than elemental sulfur.  “Cost for sulfur in elemental sulfur is six times the cost of sulfur in gypsum at current retail pricing,” Chamberlain says. 

1.     Improved Soil Quality and Increased Carbon Credits Through the Use of FGD Gypsum to Enhance No-Tillage Crop Production, Dick et al, April 28, 2006, Ohio State University unpublished report.
2.     “Leaching Losses of Sulfur During Winter Months When Applied as Gypsum, Elemental S or Prilled S”, Rhue and Kamprath, Agronomy Journal, Vol 65, No. 4, p 603-605.

 

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