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
Download citation file:
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
Figures & Tables
Organic matter (OM) in soil plays vital roles with respect to global climate change, as the largest terrestrial reservoir of organic carbon, and with respect to soil quality through the stabilization of soil structure and the retention and cycling of plant nutrients. The interactions between lay minerals and OM are central to most of these functions. Clays may catalyze formation of new humic substances, inhibit the degradation of existing humic substances through physically sequestration, and clay-humic associations are at the very heart of aggregation and soil structure stabilization. In this book we seek to explore the state of knowledge related to these topics and the analytical tools used to investigate them. In chapter 1, Hayes et al. describe chemical fractionation techniques and relate clay bound soil OM to the “humin” fraction. Chen and arcjotzly (Chapter 2) discuss the role of humic substances and polysaccarides in formation and stabilization of soil structure. Gonzalez (Chapter 3) considers the potential catalytic role of clays in the formation of new humic materials. Wershaw (Chapter 4) considers the nature of soil OM and clay-humic complexes as revealed by NMR and other techniques. The last two chapters, Chenu et al. (Chapter 5) and Laird and Thompson (Chapter 6), focus directly on understanding the nature of clay-humic complexes as revealed by electron microscopic techniques. It is hoped that this volume will provide the reader with both advanced understanding of the current state of knowledge and an appreciation for the gaps in that knowledge. The knowledge gaps represent challenges for future generations of scientists.