Plant and Soil

, Volume 76, Issue 1–3, pp 319–337 | Cite as

Soil organic matter and structural stability: mechanisms and implications for management

  • J. M. Oades
Section 6: Interaction Effects of Organisms, Organic Matter and Management on Soil Structure


The stability of pores and particles is essential for optimum growth of plants. Two categories of aggregates macro- (> 250 μm) and micro- (<250 μm) depend on organic matter for stability against disruptive forces caused by rapid wetting. Dispersion of clay particles from microaggregates is promoted by adsorption of complexing organic acids which increase the negative charge on clays. The acids are produced by plants, bacteria and fungi. However, the dispersibility of clay in microaggregates is offset by the binding action of polysaccharides, mainly mucilages produced by bacteria, but also by plant roots and fungal hyphae. The stability of microaggregates is also enhanced by multivalent cations which act as bridges between organic colloids and clays. Macroaggregates are enmeshed by plant roots, both living and decomposing, and are thus sensitive to management, and increase in number when grasses are grown and the soil is not disturbed. Lack of root growth,i.e. fallow, has the opposite effect. Various implications for management of soil structure are discussed.

Key words

Aggregates Aluminium Bacterial mucilage Binding agents Calcium Cation bridges Complexing agents Dispersion Electron microscopy Electrophoretic mobility Fungal hyphae Glues Iron Management Periodate Polysaccharides Rhizosphere Roots Slaking 


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Copyright information

© Martinus Nijhoff/Dr W. Junk Publishers 1984

Authors and Affiliations

  • J. M. Oades
    • 1
  1. 1.Department of Soil Science, Waite Agricultural Research InstituteUniversity of AdelaideGlen Osmond

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