Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: October 4, 2004
Publication Date: November 4, 2004
Citation: Olk, D.C. 2004. A chemical fractionation for structure-function relations of soil organic matter in nutrient cycling [CD-ROM]. ASA-CSSA-SSSA Annual Meeting Abstracts. Madison, WI.
To improve the relevance of chemical extractions to nutrient cycling issues, labile soil organic matter (SOM) was distinguished from recalcitrant SOM based on whether they were bound to polyvalent cations, which stabilize SOM. The unbound mobile humic acid (MHA) fraction was extracted from fresh soil by sodium hydroxide (NaOH), while the cation-bound calcium humate (CaHA) fraction was extracted by NaOH after soil decalcification. The quantity and chemical nature of the MHA were sensitive to crop management (rotation, cropping intensity, fertilizer level, tillage) in Asian rice (Oryza sativa L.) and Midwestern corn (Zea Mays L.) soils. The older, more humified CaHA fraction was intermediate between the MHA and bulk SOM in the sensitivity of its quantity and quality to crop management. Laboratory addition of the MHA to Californian vermiculitic soils reproduced the field benefit of animal manure application to maintaining potassium (K) availability, while CaHA addition did not. In a Philippine rice soil the MHA and less so the CaHA were disproportionately involved in seasonal nitrogen (N) dynamics. Because the MHA is enriched in both N and phenolic residues of woody tissues, it facilitates study of the chemical stabilization of N by phenols. Provided that polyvalent cations are removed from the soil reproducibly, this fractionation offers some insights into nutrient cycling that may not be gained through other procedures.