Clay Surface Catalysis of Formation of Humic Substances: Potential Role of Maillard Reactions
Javier M. Gonzalez, 2009. "Clay Surface Catalysis of Formation of Humic Substances: Potential Role of Maillard Reactions", 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:
Clay minerals are important from the agricultural, environmental, and industrial point of view because of their chemical and physical properties. Surface acidity of clays is of special interest given that clays catalyze several chemical organic reactions. In natural systems, research has suggested that clays play important roles in the formation of soil organic matter; however, the mechanisms of formation and the roles of clays are poorly understood and/or often controversial. Although, several different pathways of secondary synthesis leading to the formation of humic substances have been proposed, none are universally accepted (Stevenson, 1982). The Maillard reaction, condensation of reducing sugars and amino acids, is one of the proposed pathways for formation of humic substances that has received relatively little attention. The starting materials of the Maillard reaction exist in soils; the questions are whether, and to what extent, clay minerals catalyze the Maillard reaction in soil environments? The objective of this chapter is to compile a synthesis of published research on the formation of soil organic matter with emphasis on the Maillard reaction as a potential pathway for the formation of humic substances and the role of clay minerals as catalysts for Maillard reactions.
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.