Organo-Mineral Complexes and their Effects on the Physico-Chemical Properties of Soils
Yona Chen, Jorge Tarchitzky, 2009. "Organo-Mineral Complexes and their Effects on the Physico-Chemical Properties of Soils", 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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Most arable soils contain 0.1 to 5% organic matter (OM) by weight. The lowest figures represent sandy soils of arid zones, whereas the higher values are typical of clayey temperate zones. The vast majority of these soils are physically and chemically influenced by the OM which they contain. In addition to the nutritional value of the OM, it plays a critical role in the formation and stabilization of soil structure, which in turn produces desired tilth and drainage as well as resistance to erosion.
To a remarkable degree, increased OM can counteract the diverse structure effects that may prevail in either highly sandy or clayey soils. Increasing soil organic matter (SOM) content usually results in a decrease in bulk density and increase of total porosity. Over a wide range of 10 to 60 g organic C per kg soil, a curvilinear decrease in bulk density from 1.7 to 0.8 Mg m−3 has been observed (Franzluebbers et al., 2001). A curvilinear positive dependence between the C content of soils in New Zealand and aggregate stability was also shown by Haynes (2001). Friability of soils, namely, their tendency to form clods that easily crumble into their constituent natural aggregates is most commonly related to OM content as well as aggregate stability and bulk density (Macks et al., 1996).
Soil mineral particles usually aggregate into granular structures. The stability of soil aggregates (or micro-aggregates – the small particle size fraction of the aggregates – see below) is
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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.