Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 24, 2005
Publication Date: May 1, 2006
Citation: Olk, D.C., Gregorich, E.G. 2006. Overview of the symposium proceedings, "Meaningful pools in determining soil C and N dynamics". Soil Science Society of America Journal. 70(3): 967-974.
Interpretive Summary: The performance of soil in agricultural and environmental issues is strongly affected by its organic part, the soil organic matter. Soil organic matter consists of materials that range in age from weeks or months to thousands of years, so their degree of participation in recent soil performance will vary widely, complicating our ability to understand and manage soil organic matter. A common approach for studying soil organic matter is to extract it from soil in fractions that differ in age, allowing further measurements to focus on the young materials that most contribute to recent soil performance. During decades of research, multiple extraction methods have been attempted to separate soil organic matter into meaningful fractions, yet all such methods have flaws, and none is well suited for all situations. In this report we summarized the range of knowledge on real-world issues that has been gained through some of the extraction methods that are currently in use. The issues ranged from medicine to nutrient cycling in soil to water quality to movement of man-made chemicals across landscapes. We also explained the strengths and weaknesses of these methods. By discussing a broad array of methods, this report provides one of the most comprehensive and objective summaries available regarding methods for extracting soil organic matter. It will assist researchers in comparing the extraction methods and choosing the most suitable method for a given research situation.
Extraction of soil organic matter (SOM) fractions has long been an approach to elucidating the pivotal roles of SOM in soil processes. Several extraction procedures are commonly used to distinguish labile SOM fractions from non-labile fractions, and all provide partial information on SOM function. This synthesis report, in conjunction with accompanying papers on individual extraction procedures, summarizes (i) information that has been gained regarding SOM functions in real-world issues through physical or chemical fractionations, and (ii) limitations of these procedures. Physical fractionations capture the effects on SOM dynamics of the spatial arrangement of primary and secondary organomineral particles in soil, but they do not consider chemical agents for SOM stabilization. They appear more suitable for carbon (C) cycling than nitrogen (N) cycling. Chemical fractionations cannot consider the spatial arrangement, but their purely organic fractions enable advanced spectroscopic analyses for chemical characterization and can be used to elucidate molecular-level interactions between SOM and nutrients or anthropogenic compounds. Most or all fractionations share the potential for sample alteration or mixing of material among fractions. We call for better coordination of research efforts by: (i) developing integrated fractionation procedures that include physical, chemical, and/or biological components, and (ii) categorizing fractionations by their most suitable applications, defined by nutrient or compound in question, land use or crop, crop management strategies, soil type and possibly other factors. Selecting the most suitable fractionation procedure for a given research situation would enable more precise approximation of the functional SOM pool.