Submitted to: Crop Science Newsletter
Publication Type: Other
Publication Acceptance Date: 4/10/2006
Publication Date: 6/1/2006
Citation: Olk, D.C. 2006. Can we identify meaningful fractions of soil organic matter? Crop Science Newsletter. 51(6):4-5.
Technical Abstract: Soil organic matter plays a pivotal role in many agricultural and environmental issues through its involvement in the aggregation of soil particles, microbial growth, and retention of nutrients, water, pesticides and other synthetic chemicals. Understanding organic matter activity in these processes, though, is complicated by its great diversity of materials, whose ages range from days to thousands of years. Soil scientists often strive to extract organic matter from soil as meaningful fractions--ones having relevant ages and activities to the research issue at hand. Several types of fractionation procedures are commonly used. None has proven capable of isolating all the fully meaningful material, and none is the best choice for studying all research issues. Physical fractionations separate organic matter through sieving, shaking, or floating soil on dense liquids. These fractions capture the effects on organic matter dynamics of the spatial arrangement of soil particles. They have provided fundamental insights into soil carbon cycling, but not the cycling of other organic nutrients. Chemical fractionations dissolve organic matter fractions by shaking the soil in base, acid, or salt solutions. They can be used to study the behavior of nutrients and environmental contaminants (pesticides, industrial byproducts) at molecular, laboratory, and landscape scales. Biological and chemical approaches can be combined to measure the sizes and ages of active, slow, and resistant carbon pools. Future research would be aided by: (i) further developing integrated procedures that include combinations of physical, chemical, and/or biological separations, and (ii) identifying the most suitable procedures for specific issues.