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Nature of the association of organic carbon with soil microaggregates.

Kaye M. Spark and Roger S. Swift.

Faculty of Natural Resources, Agriculture and Veterinary Science, University of Queensland, Gatton, QLD 4343, Australia. http://www.uq.edu.au/. Email kaye.spark@uqg.uq.edu.au.

Abstract

Primary soil particles within micro-aggregates are bound together by physical, chemical and biological processes. Aggregation of primary soil particles to form microaggregates is essential in the development of improved soil structure. In addition incorporation of organic compounds into these aggregates contributes to the sequestration of soil carbon and hence, the reduction of greenhouse gas formation. This study is concerned with advancing the understanding of how organic carbon is sequestered in soil microaggregates.

Ferrosol soils, from pastures and forested sites, have been used to investigate the nature of the microaggregate structure in the soils as a function of the nature of the surface vegetation, and soil depth, and the how the organic matter is associated with the aggregate. The soils were fractionated using a combination of wet-sieving and particle settling techniques before analysis. The impact of the solution pH during extraction, before and after sonication, on the particle size and organic carbon content of the whole soils, and soil fractions, is discussed in terms of the nature of the interaction between the component particles from which the initial aggregates are formed. These conclusions are correlated with the observed solubility of the organic matter to determine the significance of the aggregation mechanisms on the sequestration of the carbon compounds.

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