Characterize Organic and Reduced Inorganic Sulfur in Soils By Multi-Element Scanning Thermal Analysis (MESTA).

Soil organic sulfur has been much less studied than other major essential elements because, at least in part, the tediousness of the methodology involved. Recent development of the multi-element scanning thermal analysis (MESTA) technology, however, enables one to analyze organic and reduced inorganic sulfur species in soils directly and conveniently. We studied the forms of soil sulfur by MESTA. Preliminary results show that upland soils contained organic sulfur in relatively simple forms of amino acids or its immediate derivatives. The amount of organic sulfur in cultivated soils was reduced when compared with that in their non-cultivated counterparts. Wetland soils had three more categories of sulfur in additional to the amino acid forms: the organic sulfur formed by the reactions between soil organic matter and hydrogen sulfide, the metal sulfides and elemental sulfur. Metal sulfides and elemental sulfur were easily oxidized to sulfate when anaerobic conditions were removed. The organic sulfur formed due to the reactions between soil organic matter and hydrogen sulfide, however, could be preserved for months or years and thus can serve as an evidence of soil submergence in the recent history of the soil.