The Ultrastructure of Clay-Humic Complexes in an Iowa Mollisol
David A. Laird, Michael L. Thompson, 2009. "The Ultrastructure of Clay-Humic Complexes in an Iowa Mollisol", Carbon Stabilization by Clays in the Environment: Process and Characterization Methods, David A. Laird, Javiera Cervini Silva, Yona Chen, Claire Chenu, Françoise Elsass, Javier M. Gonzalez, Michael H.B. Hayes, David A. Laird, Alain Plante, Andre J. Simpson, Guixue Song, Jorge Tarcjotzly, Michael L. Thompson, I. Virto, Robert L. Wershaw
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The chemical and physical activity of clay minerals in soils, particularly in surface horizons, is significantly mediated by interactions with organic components. And the reactivity of soil organic matter, including its resistance to decomposition, is regulated by interactions with clay minerals. This marriage of organic and inorganic soil components has profound implications for our ability to quantitatively predict the consequences of alternative soil management practices that could improve food and energy production, protect water and air quality, or mitigate the impacts of greenhouse gases on global climate.
In this paper, we discuss observations of clay-humic complexes made by electron microscopy and other complementary techniques. By “clay,” we mean secondary layer silicate and oxide minerals that are common to soils. By “humic materials,” we mean soil organic matter that was derived from biological tissue but has been so transformed in the soil environment that it lacks any recognizable biological structures. Our definition of humic materials precludes any genetic or functional relationship with humic and fulvic acids, which are procedurally defined extracts of soil organic materials that we view as heterogeneous mixtures of hydrolyzed humic material, biological tissue, and black C. Data reported in this paper come from various analyses of a single smectite-rich Mollisol in Iowa. Because we investigated only one soil, we cannot generalize our results beyond saying that the studied soil was typical of smectite-rich Mollisols in the upper Midwest.
Interactions between soil organic matter (SOM) and soil minerals are primarily responsible for the formation and stabilization of soil structure