1 Organic Matter in Soils: Pools, Distribution,
Transformations, and Function ................................ 1
Pools of Organic Matter in Soils ............................. 1
Organic Matter (Humus) Content of Soils ...................... 6
Decomposition Processes and Ages of Organic Matter .......... 11
Function of Organic Matter in Soil .......................... 14
Organic Matter and Sustainable Agriculture .................. 19
Environmental Significance of Humic Substances .............. 19
Summary ..................................................... 20
References .................................................. 21
2 Extraction, Fractionation, and General Chemical
Composition of Soil Organic Matter .......................... 24
Brief Historical Review ..................................... 24
Associations of Organic Matter in Soil ...................... 34
Extraction Methods .......................................... 34
Fractionations Based on Solubility Characteristics .......... 41
Purification ................................................ 45
Classification and Distribution of Dissolved Organic С
(DOC) ....................................................... 51
Comparison of Soil Humic Substances with Those of Other
Environments ................................................ 54
Physical Fractionation of Organic Matter .................... 54
Summary ..................................................... 55
References .................................................. 56
3 Organic Forms of Soil Nitrogen .............................. 59
Fractionation of Soil N ..................................... 59
Nitrogen in Humic and Fulvic Acids .......................... 66
Biochemical N Compounds ..................................... 71
Biomass N ................................................... 89
Natural Variations in N Isotope Abundance ................... 90
l5N-NMR Spectroscopy ........................................ 90
Stability of Soil Organic N ................................. 90
Summary ..................................................... 91
References .................................................. 92
4 Native Fixed Ammonium and Chemical Reactions of Organic
Matter with Ammonia and Nitrite ............................. 96
Levels of Native Fixed NH4+ in Soils ........................ 96
The C/N Ratio .............................................. 100
Chemical Reactions of NH3 and NO2- with Organic Matter ..... 102
Summary .................................................... 110
References ................................................. 111
5 Organic Phosphorus and Sulfur Compounds .................... 113
The C/N/P/S Ratio .......................................... 113
Soil Organic P ............................................. 115
Soil Organic S ............................................. 128
Summary .................................................... 137
References ................................................. 137
6 Soil Carbohydrates ......................................... 141
Significance of Soil Carbohydrates ......................... 142
Structure and Classification ............................... 142
State in the Soil .......................................... 144
Quantitative Determination of Soil Carbohydrates ........... 154
Summary .................................................... 163
References ................................................. 164
7 Soil Lipids ................................................ 166
Lipid Content of Soil Humus ................................ 166
Function in Soil ........................................... 171
Composition ................................................ 175
Summary .................................................... 185
References ................................................. 185
8 Biochemistry of the Formation of Humic Substances .......... 188
Major Pathways of Humus Synthesis .......................... 188
The Lignin Theory .......................................... 191
The Polyphenol Theory ...................................... 197
Sugar-Amine Condensation ................................... 206
Scheme for the Formation of Humic Substances ............... 208
Summary .................................................... 209
References ................................................. 210
9 Reactive Functional Groups ................................. 212
Elemental Content .......................................... 212
Methods of Functional Group Analysis ....................... 214
Distribution of Oxygen-Containing Functional Groups ........ 226
Diagenetic Transformations ................................. 231
Summary .................................................... 234
References ................................................. 234
10 Structural Components of Humic and Fulvic Acids as
Revealed by Degradation Methods ............................ 236
Experimental Approaches .................................... 236
Hydrolysis Methods ......................................... 238
Reductive Cleavage ......................................... 240
Oxidative Methods .......................................... 248
Miscellaneous Chemical Approaches .......................... 254
Thermal Methods ............................................ 255
Summary .................................................... 256
References ................................................. 257
11 Characterization of Soil Organic Matter by NMR
Spectroscopy and Analytical Pyrolysis ...................... 259
Theory of Nuclear Magnetic Resonance Spectroscopy (NMR) .... 259
Techniques for l3C-NMR Spectroscopy ........................ 263
l3C-NMR Spectroscopic Analysis of Humic and Fulvic
Acids ...................................................... 265
l3C-NMR Spectroscopic Analysis of Soil Organic Matter In
Situ ....................................................... 272
lH-NMR Spectroscopy ........................................ 274
l5N-NMR Spectroscopy ....................................... 276
31P-NMR Spectroscopy ....................................... 277
Analytical Pyrolysis ....................................... 277
Summary .................................................... 281
References ................................................. 281
12 Structural Basis of Humic Substances ....................... 285
General Considerations ..................................... 286
Type Structures for Humic and Fulvic Acids ................. 287
Unique Feature of Humic Substances in Seawater ............. 294
A Simplified Structural Representation of Soil Humic
Substances ................................................. 294
Summary .................................................... 301
References ................................................. 301
13 Spectroscopic Approaches ................................... 303
Ultraviolet (UV) and Visible Regions ....................... 304
Infrared (IR) Spectroscopy ................................. 307
Electron Spin Resonance (ESR) Spectroscopy ................. 317
Fluorescence Spectroscopy .................................. 322
Summary .................................................... 322
References ................................................. 323
14 Colloidal Properties of Humic Substances ................... 325
The Colloidal State ........................................ 325
Molecular Weights and Particle Sizes ....................... 326
Morphological Features by Electron Microscopy .............. 339
Structural Evaluation by X-Ray Diffraction ................. 341
Small-Angle X-Ray Scattering ............................... 342
Size Evaluation by Gel Filtration .......................... 343
Summary .................................................... 347
References ................................................. 348
15 Electrochemical and Ion-Exchange Properties of Humic
Substances ................................................. 350
Acidic Nature of Humic and Fulvic Acids .................... 351
Selectivity of Humic Substances for Exchange Cations ....... 367
Contribution of Organic Matter to the Cation-Exchange
Capacity (CEC) of the Soil ................................. 367
Coagulation of Humic Substances by Polyelectrolytes ........ 372
Electrophoresis ............................................ 373
Oxidation-Reduction Potential .............................. 374
Summary .................................................... 375
References ................................................. 375
16 Organic Matter Reactions Involving Metal Ions in Soil ...... 378
Properties of Metal-Organic Matter Complexes ............... 379
Significance of Chelation Reactions in Soil ................ 381
Forms of Transition Metal Ions in Soil ..................... 384
Biochemical Compounds as Chelating Agents .................. 388
Trace Metal Interactions with Humic Substances ............. 394
Summary .................................................... 401
References ................................................. 401
17 Stability Constants of Metal Complexes with Humic
Substances ................................................. 405
General Considerations ..................................... 405
Modeling Approaches ........................................ 408
Summary .................................................... 427
References ................................................. 427
18 Clay-Organic Complexes and Formation of Stable
Aggregates ................................................. 429
Nature of Clay Colloids .................................... 429
Adsorption of Defined Organic Compounds by Clay ............ 431
Naturally Occurring Clay-Organic Complexes ................. 439
Role of Organic Matter in Forming Stable Aggregates in
Soil ....................................................... 445
Soil Wettability ........................................... 449
Summary .................................................... 450
References ................................................. 450
19 Organic Matter Reactions Involving Pesticides in Soil ...... 453
Humus Chemistry in Relation to Pesticide Behavior .......... 455
Adsorption Mechanisms ...................................... 462
Relative Affinities of Pesticides for Soil Organic
Matter ..................................................... 469
Summary .................................................... 469
References ................................................. 469
20 Role of Organic Matter in Pedogenic Processes .............. 472
Weathering of Rocks and Minerals ........................... 473
Neogenesis of Minerals ..................................... 477
Translocation of Mineral Matter and Horizon
Differentiation ............................................ 478
Organic Matter and Soil Classification ..................... 483
Paleohumus ................................................. 485
Effects of Acidic Inputs (Acid Rain) on Pedogenic
Processes .................................................. 485
Summary .................................................... 486
References ................................................. 486
Index ......................................................... 489
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