Humic Matter in Soil and the Environment: Principles and Controversies - Chapter 1 ppt

Tan Soil Erosion, Conservation, and Rehabilitation, edited by Menachem Agassi Plant Roots: The Hidden Half, Second Edition, Revised and Expanded, edited by Yoav Waisel, Amram Eshel, a

Humic Matter in Soil

and the Environment Principles and Controversies

Kim H Tan

University of Georgia Athens, Georgia, U.S.A

M A R C E L

MARCEL DEKKER, INC

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PREFACE

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 ofwhether

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 a t 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 asprecursors, and

distinguished into (I) 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

biopolyrner degradation andlor 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 hurnic 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, E/f, 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 mat-

ter Negative and positive charges are examined and their magnitude

is explained using the Henderson-Hasselbalch equation, pKa, and pK,,

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 adsorp-

tion, 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 pK, 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 bio-

logical 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 preser-

vation 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 ofhumic 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

Kim H Tan

CONTENTS

Preface

Chapter 1 THE ISSUE OF HUMIC MATTER

1.1 Concept of Humus

1.1.1 The Early Concept of Humus

1.1.2 Concept of Humus in the Third Millennium

1.2 Concept of Humic Matter

1.3 The Issue of Artifacts

1.4 The Issue of Real Compounds

1.5 The Issue of Chemical Composition

Chapter 2 THE NATURE AND DISTRIBUTION

OF HUMIC MATTER

2.1 Concepts and Historical Background

2.1.1 Historical Concepts

2.1.2 Concepts in the Early Twentieth Century

2.1.3 The Dawn of Modern Concepts

2.2 Distribution of Humic Matter

2.2.1 Humic Matter in Soils

2.2.2 Humic Matter in Soils of the Wetlands

2.2.3 Humic Matter in Aquatic Environments

2.2.4 Humic Matter in Geologic Deposits

2.2.5 Humic Matter in Agricultural, Industrial

and Municipal Waste

2.3 Classification of Humic Matter

Terrestrial or Terrigenous Humic Matter Aquatic Humic Matter

Wetland or Peat Humic Matter Geologic Humic Matter

Anthropogenic Humic Matter

Chapter 3 EXTRACTION AND FRACTIONATION

3.2.1 Extraction Methods

Fractionation of Humic Substances

3.3.1 Fractionation of Humic Acid

3.3.2 Fractionation of Fulvic Acid

Aquatic Humic Matter

3.4.1 Extraction Methods

3.4.2 Fractionation of Aquatic Humic Matter

Types of Humic Substances

3.5.1 Fulvic Acid

3.5.2 Humic Acid

3.5.3 Humin

Chapter 4 GENESIS OF HUMIC MATTER

4.1 Major Pathways of Humification

4.2 Precursors of Humic Matter

4.2.1 Lignin

4.2.2 Phenols and Polyphenols

4.3.1 The Ligno-Protein Theory

4.3.2 The Phenol-Protein Theory

4.3.3 The Sugar-Amine Condensation Theory

4.4 Statistical Modeling of Humification

Phenol-Protein Concept 5.2.3 Structures Based on the

Sugar-Amine Condensation Concept

5.3 Computer Modeling of Humic Acid Structures

Chapter 6 CHARACTERIZATION OF HUMIC

SUBSTANCES

6.1 Chemical Characterization

6.2 Molecular Weights

6.2.1 Number-Average Molecular Weight, M,,

6.2.2 Weight Average Molecular Weight, M,

6.2.3 Z-Average Molecular Weight, M,

6.2.4 Characterization by Molecular Weight

6.2.5 Relationship between Molecular Weight

and Size or Shape 6.3 Ultraviolet and Visible Light Spectrophotometry

6.4 Infrared Spectroscopy

6.4.1 Infrared Spectra of Humic Matter

6.4.2 Classification of Infrared Spectra

6.5 Nuclear Magnetic Resonance Spectroscopy

6.5.1 Electron Paramagnetic Resonance

6.5.2 Carbon-13 Nuclear Magnetic Resonance

6.5.3 Nitrogen-15 Nuclear Magnetic Resonance

6.5.4 Phosphorus-31 Nuclear Magnetic Resonance

6.6 Electron Microscopy of Humic Matter

6.6.1 Transmission Electron Microscopy

6.6.2 Scanning Electron Microscopy

Chapter 7 ELECTROCHEMICAL PROPERTIES

OF HUMIC MATTER

7.1 Origin and Types of Electric Charges

7.1.1 Negative Charges

7.1.2 Positive Charges

7.2 Surface Charge Density

7.3 Electric Double Layer

7.3.1 Fused Double Layer

7.4 Chemical Reactions and Interactions

7.4.1 Adsorption

7.4.2 Cation Exchange Capacity