Sách báo tài liệu nông nghiệp

[EBOOK] Humic Matter in Soil and the Environment (Principles and Controversies), Kim H. Tan (University of Georgia Athens, Georgia, U.S.A), Published by Marcel Dekker, Inc.

A large amount of information has accumulated on humic acids and related substances, which warrants the creation of an independent science of humic compounds. Two different concepts have emerged from the maze of data, one claiming humic compounds to be operational or fake compounds, produced by the analytical extraction procedures, and the other considering them to be natural compounds occurring in soils, rivers, lakes, oceans and their sediments. Apparently the two opposing opinions have caused considerable confusion among scientists, students, and professionals alike about exactly what humic acid is, or what the difference is between soil organic matter, humus, and humic acid. Several of the books and especially the symposium proceedings on humus and soil organic matter are guilty of making the chaos worse, by using different terms and concepts interchangeably and by only covering “specialty” topics. The need for a book providing comprehensive coverage, on definitions, concepts, genesis, extraction, properties, and the impact of humic matter on agriculture, industry, and environment, is apparent.

This book tries to address the problem of complete coverage as highlighted above. In addition to its value as a textbook, it can be used equally well as a reference book by all interested in humic matter. The issues and controversies associated with humic acids are analyzed from the two different viewpoints mentioned above. The advances of the past century, and the prospects for advancing humic acid science in the new millennium, are explored from both viewpoints. The text also carries a message for increasing awareness of the appearance of more and more data, emphasizing the ubiquitous presence of humic compounds in nature and their impact on the environment, soils, and agriculture. The intensified application of humic substances in industrial and pharmaceutical operations is discussed, underscoring the significance of humic acids as highly important organic substances in nature. The production and use of therapeutic chemicals from humic acids and the manufacture of commercial humates for use in soils, which has grown lately into a multimillion dollar business, are addressed. These are issues of considerable interest to people studying, practicing, and producing medicines and fertilizers, and therefore enlarges the audience for this book beyond the scope of soil, agricultural, and chemical science.

The book starts by examining the concepts of humus and humic matter from the two different standpoints. Definitions are given in Chapter 1 to delineate soil organic matter, humus, and humified substances. The term “humic matter” is defined and adopted in this book as the humified fraction of humus, and the controversy of whether it is present as an artifact or as a true compound in nature is addressed. Questions are raised on the significance of studying fake compounds, especially in institutions where “publish or perish” prevails.

Chapter 2 discusses the nature and distribution of humic matter in soils, wetlands and peat, in aquatic environments, and in geologic deposits. A classification of the different types of humic matter based on origin is provided. The chapter contains a discussion of anthropogenic humic matter, developed from agricultural waste, polluting the environment. The notorious deposits from the so-called CAFOS, confined animal feeding operations, located on top of the recharge zones of aquifers in Texas, are explained as being too close for comfort. The topic of domestic waste, fouling drainage ditches and canals, is included to cover humic matter produced by these rotten pollutants.

Extraction, isolation, and fractionation of humic substances are featured in Chapter 3, starting with the search for the ‘best’ inorganic and organic reagents. Detailed analytical procedures are given according to the International Humic Substances Society, the Soil Science Society of America, and the methods presented by Stevenson and Tan. The extraction of aquatic humic matter is discussed separately and the use ofXAD resins evaluated. A descriptive analysis is provided at the end on fulvic acids, humic acids, and humin, highlighting their definitions, properties, and significance in soils.

Chapter 4 is on the genesis of humic matter. The components from which humic matter is formed are defined here as precursors, and distinguished into (1) major precursors, e.g., lignin, phenols, quinones, protein, amino acids, and carbohydrates, and (2) miscellaneous humic precursors, e.g., lipids, sterols, and nucleic acids. Growth promoting substances such as auxin, gibberellin, and vitamins are included in the latter group, and their biotic origin and decomposition are examined in relation to claims that humic acids display hormone-like actions. The section above is then followed by a probing discussion of the processes of formation of humic matter, defined here as humification. The three major theories, ligno-protein, phenol-protein, and sugar-amine condensation theory, are addressed in relation to the biopolymer degradation and/or polymerization or condensation concept. As a final topic, a detailed analysis is given of the significance of statistical modeling of humification, including the use of stability coefficients, humification indexes, and models.

Chapter 5 discusses the chemical composition of humic matter, which is distinguished into an elemental and a group composition. The significance of using weight and atomic percentages is studied, underscoring the importance of C/N ratios, atomic ratios, and functional group contents in the formation of formula composition. Molecular structures of humic acids are created by applying simple basic reactions, and the structural models obtained by the newest advances in computer modeling are a major challenge to the idea that humic substances lack formulas and structures.

Chapter 6 is about characterization of humic substances by molecular weight and spectroscopic analysis. The types and ranges of molecular weight values are described, and their effect on size and shape of humic molecules is evaluated, including the importance of frictional ratios, ĩỉfa. The usefulness of spectrophotometric color ratios and infrared group frequency and fingerprint regions in the identification of fulvic and humic acids is studied. Characterization by electron spin resonance (ESR), nuclear magnetic resonance (NMR), and electron microscopy is addressed in detail. Characteristic visible light, infrared, ESR, and NMR spectra and electron micrographs are provided, with detailed descriptions for each of the humic compounds. They are valuable for classroom teaching, and/or for use as standard reference in research and other scientific or industrial analysis; hence they are assets that make this book stand out over any other book published on the subject.

Chapter 7 discusses electrochemical properties of humic matter. Negative and positive charges are examined and their magnitude is explained using the Henderson-Hasselbalch equation, pKa, and pKị, values. The issue of COOH and phenolic-OH group contents affecting negative charges and total acidity of humic matter is addressed. Definitions and formulation of surface charge density are studied and the electric double layer theories amended to include a new concept called fused double layer. The proper definitions are given for adsorption, cation exchange, complex, chelation, and bridging reactions, and deviations from the concepts are questioned as aberrations. The importance of these interactions in soils, agriculture, and the environment are addressed, and the role of pKa and stability constants in the reactions evaluated.

The agronomic importance of humic matter is featured in Chapter 8, highlighting its effect on soil physical, chemical, and biological properties. The significance of humic matter for terrestrial and aquatic life is explained, and the role of humic matter in the carbon and nitrogen cycles underscored. The action of humic acids as a redox agent is analyzed in the overall soil’s redox system. The direct and indirect effect of humic matter on plant growth and crop production are discussed in detail.

Chapter 9 covers the environmental and industrial importance of humic matter. The outstanding role humic matter plays in preservation of soil organic matter, mobilization and immobilization of elements, and biological detoxification is presented by underscoring the issue of degradation of the soil ecosystem. The use of humic matter in industry is discussed, stressing the production of agrochemicals, e.g., biofertilizers and biopesticides, and the salient features of humic acids considered for use as drilling fluids, paint, ink, tanning, ceramics, and silicones. An assessment is also made of the increased importance of commercial humates, and their production, types, and controversies over their use as fertilizers are addressed. The significance of humic matter as a source for the production of pharmaceuticals is examined, and claims of humic acid derived medicines for antiviral, anticancer, and eye disease treatments is discussed.

Finally, I would like to acknowledge the scientists and publishers who offered their generous support. Special thanks are due to Dr. Hans-Rolf Schulten, Professor, Institute for Soil Science, Rostock University, Rostock, Germany, for his generosity in supplying from his personal files the 3D-structural models of humic acids. Thanks are also conveyed to Dr. Patrick G. Hatcher, Professor and Co-Director, Ohio State University EMSI, Department of Chemistry, Newman and Wolfram Laboratory, Ohio State University, Columbus, Ohio, for his permission to use his 2D-structural model of humic acid. Appreciation is extended to the American Chemical Society, Washington, D.C., and to Elsevier Publishers, UK and Amsterdam, for their approval to quote or reproduce figures or photographs. Last but not least, I wish to thank my wife for her loyal assistance and encouragement, enabling me to devote my time and efforts to producing this book.

[EBOOK] Humic Matter in Soil and the Environment (Principles and Controversies), Kim H. Tan (University of Georgia Athens, Georgia, U.S.A), Published by Marcel Dekker, Inc.

Keyword: ebook, giáo trình, Humic Matter in Soil and the Environment, Principles and Controversies, humic trong đất, humic trong môi trường, chất humic trong đất
Xem thêm