Sulfur Forms and Cycling Processes in Soil and Their Relationship to Sulfur Fertility
- Jeff J. Schoenau and
- Sukhdev S. Malhi
Sulfur may be present in soil in a variety of organic and inorganic forms. In well-drained, upland agricultural soils, organic forms of sulfur dominate, while inorganic sulfate is the main inorganic sulfur form. Sulfate present in soil solution represents immediately plant-available sulfur. The microbial conversion of organic sulfur in the form of humus and crop residues to sulfate, termed mineralization, is a dominant mechanism for replenishment of available sulfur. Typically, 1 to 5% of the organic sulfur in a soil is mineralized to sulfate over a growing season. Warm, moist soils with large amounts of organic matter containing easily mineralized organic sulfates exhibit the highest mineralization rates. Microbial oxidation of sulfur is also an important process when reduced sulfur fertilizers such as elemental sulfur are added to soil. Like mineralization, the oxidation of reduced sulfur forms to sulfate is maximized when soils are warm and near field capacity moisture content. The conversion of elemental sulfur fertilizers to plant-available sulfate is increased when particle size is small and the particles are dispersed in the soil. Sulfate can be adsorbed to minerals and organic matter surfaces in soils of acid pH. A portion of the adsorbed sulfate is plant available and adsorption can be beneficial by reducing leaching losses in humid environments. In semiarid environments, sulfate salts can accumulate within the soil profile, especially when drainage is restricted. Sulfates found at depth in the soil profile can contribute to supplies of plant-available sulfur later in the growing season.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
Copyright © 2008. American Society of Agronomy, Crop Science Society of America, Soil Science Society of America, 5585 Guilford Road, Madison, WI 53711-5801, USA. Sulfur: A Missing Link between Soils, Crops, and Nutrition. Agronomy Monograph 50.