Mineralization Potential of Sulfur From Soil Organic Matter and Elemental Sulfur in Minnesota Soils.

Soil organic matter can supply a large portion of sulfur (S) needed for crop production.  Since soils can significantly vary in their physical and chemical properties, it is critical to evaluate the mineralization potential of sulfur in Minnesota soils.   In addition, elemental S use is becoming more widespread as farmers apply fertilizer out of concern of S deficiencies occurring.  The objective of this study is to determine a relationship between the amount of sulfate-S and soil organic matter concentration and the potential for mineralization of elemental S in twenty-six benchmark soils from major commodity crop growing regions in Minnesota.  Soil was collected from the top 15 cm.  Soil organic matter concentration in twenty-six soils ranged from 13 to 89 g kg^-1. Forty grams of soil were incubated in leaching columns at 35^oC.  Treatments consisted of a control (no S) and 100 mg S kg^-1 as elemental sulfur and gypsum (calcium sulfate).  Each column was put under a vacuum and 150 mL of deionized water was drawn through the columns at 0, 14, 28, 56, 84, 112, and 140 days.  The initial leaching recovered between 80-90% of the sulfate-S from the gypsum treatment.  No sulfate-S was leached from the elemental S treatment until the leaching at the 14th day, and the majority of the mineralization sulfate-S occurred by the 56th day leaching where nearly all elemental S was mineralized to sulfate.  Overall, the cumulative amount of sulfate-S leached was linearly related to soil organic matter concentration.  All soils have the capacity to convert elemental S but the completed oxidation of elemental S is still a slow process under high temperatures.