4. FOREWORD
This new book by Marc Pansu and Jacques Gautheyrou provides a
synopsis of the analytical procedures for the physicochemical analysis of
soils. It is written to conform to analytical standards and quality control.
It focuses on mineralogical, organic and inorganic analyses, but also
describes physical methods when these are a precondition for analysis. It
will help a range of different users to choose the most appropriate method
for the type of material and the particular problems they have to face. The
compiled work is the product of the experience gained by the authors in
the laboratories of the Institute of Research for Development (IRD) in
France and in tropical countries, and includes an extensive review of the
literature. The reference section at the end of each chapter lists source
data from pioneer studies right up to current works, such as, proposals for
structural models of humic molecules, and itself represents a valuable
source of information.
IRD soil scientists collected data on Mediterranean and tropical
soils in the field from West and North Africa, Madagascar, Latin
America, and South East Asia. Soil materials from these regions are often
different from those found in temperate zones. As their analysis brought
new problems to light, it was essential to develop powerful and specific
physicochemical methods. Physicists, chemists and biologists joined
forces with IRD soil scientists to contribute knowledge from their own
disciplines thereby widening its scope considerably. This work is the fruit
of these experiments as applied to complex systems, involving soils and
the environment.
The methodological range is particularly wide and each chapter
presents both simple analyses and analyses that may require sophisticated
equipment, as well as specific skills. It is aimed both at teams involved in
practical field work and at researchers involved in fundamental and
applied research. It describes the principles, the physical and chemical
basis of each method, the corresponding analytical procedures, and the
constraints and limits of each. The descriptions are practical, easy to
understand and implement. Summary tables enable a rapid overview of
the data. Complex techniques are explained under the heading ‘Principle’
and concrete examples of methods include: spectra (near and far IR, UV-
visible, 1H-NMR, 13C-NMR, ESR, ICP-AES, ICP-MS, X-ray
fluorescence, EDX or WDX microprobe, neutron activation analysis),
diffractograms (XRD, electron microdiffraction), thermograms (DTA,
DTG, TGA), chromatograms (GPC, HPLC, ionic chromatography,
exclusion chromatography), electrophoregrams, ion exchange methods,
electrochemistry, biology, different physical separation techniques,
selective dissolutions, and imagery.
5. VI Foreword
The book will be valuable not only for researchers, engineers, technicians
and students in soil science, but also for agronomists and ecologists and
others in related disciplines, such as, analytical physical chemistry,
geology, climatology, civil engineering and industries associated with
soil. It is a basic work whose goal is to contribute to the scientific
analysis of the environment. The methodologies it describes apply to a
wide range of bioclimatic zones: temperate, arid, subtropical and tropical.
As with the previous books by the same authors (Pansu, Gautheyrou and
Loyer, 1998, Masson, Paris, Milan, Barcelona; Pansu, Gautheyrou and
Loyer, 2001, Balkema, Lisse, Abington, Exton, Tokyo), this new book
represents a reference work for our laboratories. We are confident its
originality and ease of use will ensure its success.
Alain Aventurier, Director of Analytical Laboratories of CIRAD1
Christian Feller, Director of Research at IRD 2
Pierre Bottner, Director of Research at CNRS 3
1
CIRAD, Centre International pour la Recherche Agronomique et le
Développement (France).
2
IRD, Institut de Recherche pour le Développement (ex ORSTOM, France).
3
CNRS, Centre National de la Recherche Scientifique (France).
6. CONTENTS
PART 1 - MINERALOGICAL ANALYSIS
CHAPTER 1 Water Content and Loss on Ignition
1.1 Introduction ..................................................................................................3
1.2 Water Content at 105°C (H2O−) ....................................................................6
1.2.1 Principle .................................................................................................6
1.2.2 Materials ................................................................................................6
1.2.3 Sample...................................................................................................6
1.2.4 Procedure ..............................................................................................7
1.2.5 Remarks ................................................................................................7
+
1.3 Loss on Ignition at 1,000°C (H2O ) ..............................................................8
1.3.1 Introduction ............................................................................................8
1.3.2 Principle ...............................................................................................11
1.3.3 Equipment............................................................................................11
1.3.4 Procedure ............................................................................................11
1.3.5 Calculations .........................................................................................12
1.3.6 Remarks ..............................................................................................12
Bibliography .....................................................................................................12
CHAPTER 2 Particle Size Analysis
2.1 Introduction ................................................................................................15
2.1.1 Particle Size in Soil Science ................................................................15
2.1.2 Principle ...............................................................................................17
2.1.3 Law of Sedimentation ..........................................................................18
2.1.4 Conditions for Application of Stokes Law.............................................24
2.2 Standard Methods ......................................................................................26
2.2.1 Pretreatment of the Sample .................................................................26
2.2.2 Particle Suspension and Dispersion ....................................................31
2.2.3 Pipette Method after Robinson-Köhn or Andreasen ............................35
2.2.4 Density Method with Variable Depth ....................................................42
2.2.5 Density Method with Constant Depth...................................................47
2.2.6 Particle Size Analysis of Sands Only ...................................................48
2.3 Automated Equipment ...............................................................................50
2.3.1 Introduction ..........................................................................................50
2.3.2 Method Using Sedimentation by Simple Gravity..................................51
2.3.3 Methods Using Accelerated Sedimentation .........................................53
2.3.4 Methods Using Laser Scattering and Diffraction..................................54
2.3.5 Methods Using Optical and Electric Properties....................................55
2.3.6 Methods Allowing Direct Observations of the Particles........................55
2.3.7 Methods Using Conductivity ................................................................56
References ........................................................................................................56
Bibliography .....................................................................................................58
Generality .....................................................................................................58
7. VIII Contents
Pre-treatment................................................................................................58
Pipette Method..............................................................................................61
Hydrometer Method ......................................................................................62
Instrumental Methods ...................................................................................62
CHAPTER 3 Fractionation of the Colloidal Systems
3.1 Introduction ................................................................................................ 65
3.2 Fractionation by Continuous Centrifugation........................................... 66
3.2.1 Principle............................................................................................... 66
3.2.2 Theory ................................................................................................. 69
3.2.3 Equipment and reagents ..................................................................... 73
3.2.4 Procedure............................................................................................ 75
3.3 Pretreatment of the Extracted Phases ..................................................... 79
References........................................................................................................ 81
Bibliography ..................................................................................................... 81
CHAPTER 4 Mineralogical Characterisations by X-Ray Diffractometry
4.1 Introduction ................................................................................................ 83
4.1.1 X-Ray Diffraction and Mineralogy ........................................................ 83
4.1.2 Principle............................................................................................... 86
4.1.3 XRD Instrumentation ........................................................................... 87
4.2 Qualitative Diffractometry.......................................................................... 90
4.2.1 Overview of Preparation of the Samples ............................................. 90
4.2.2 Preparation for Powder Diagrams ....................................................... 90
4.2.3 Preparation for Oriented Diagrams...................................................... 94
4.2.4 Pretreatment of Clays.......................................................................... 99
4.2.5 Qualitative Diffractometry ..................................................................113
4.3 Quantitative Mineralogical Analysis .......................................................118
4.3.1 Interest ..............................................................................................118
4.3.2 Quantitative Mineralogical Analysis by XRD......................................118
4.3.3 Multi-Instrumental Quantitative Mineralogical Analysis......................124
References......................................................................................................126
Bibliography ...................................................................................................127
General.......................................................................................................127
Preparation of Oriented Aggregates on Porous Ceramic Plate ..................128
Saturation of Clays by Cations ...................................................................129
Saturation, Solvation, Intercalation Complex, Dissolution ..........................129
Preparation of Iron Oxides..........................................................................130
Quantitative XRD........................................................................................130
CHAPTER 5 Mineralogical Analysis by Infra-Red Spectrometry
5.1 Introduction ..............................................................................................133
5.1.1 Principle.............................................................................................133
5.1.2 IR Instrumentation .............................................................................135
5.2 IR Spectrometry in Mineralogy................................................................138
5.2.1 Equipment and Products ...................................................................138
5.2.2 Preparation of the Samples ...............................................................139
5.2.3 Brief Guide to Interpretation of the Spectra....................................... 146
5.2.4 Quantitative Analysis .........................................................................152
8. Contents IX
5.3 Other IR Techniques ................................................................................156
5.3.1 Near-infrared Spectrometry (NIRS)................................................... 156
5.3.2 Coupling Thermal Measurements and FTIR Spectrometry of Volatile
Products ............................................................................................158
5.3.3 Infrared Microscopy ...........................................................................159
5.3.4 Raman Scattering Spectroscopy ...................................................... 159
References......................................................................................................161
Chronobibliography.......................................................................................162
CHAPTER 6 Mineralogical Separation by Selective Dissolution
6.1 Introduction ............................................................................................. 167
6.1.1 Crystallinity of Clay Minerals............................................................. 167
6.1.2 Instrumental and Chemical Methods ................................................ 169
6.1.3 Selective Dissolution Methods .......................................................... 172
6.1.4 Reagents and Synthetic Standards .................................................. 174
6.2 Main Selective Dissolution Methods...................................................... 180
6.2.1 Acid Oxalate Method Under Darkness (AOD)................................... 180
6.2.2 Dithionite-Citrate-Bicarbonate Method (DCB) ................................... 187
6.2.3 EDTA Method ................................................................................... 192
6.2.4 Pyrophosphate Method..................................................................... 196
6.2.5 Extraction in Strongly Alkaline Mediums ........................................... 201
6.3 Other Methods, Improvements and Choices ........................................ 206
6.3.1 Differential Sequential Methods ........................................................ 206
6.3.2 Selective Methods for Amorphous Products ..................................... 210
6.3.3 Brief Overview to the Use of the Differential Methods ...................... 214
References ..................................................................................................... 215
CHAPTER 7 Thermal Analysis
7.1 Introduction ............................................................................................. 221
7.1.1 Definition........................................................................................... 221
7.1.2 Interest.............................................................................................. 223
7.2 Classical Methods ................................................................................... 226
7.2.1 Thermogravimetric Analysis.............................................................. 226
7.2.2 Differential Thermal Analysis and Differential Scanning Calorimetry 235
7.3 Multi-component Apparatuses for Thermal Analysis........................... 246
7.3.1 Concepts........................................................................................... 246
7.3.2 Coupling Thermal Analysis and Evolved Gas Analysis..................... 247
References ..................................................................................................... 249
Chronobibliography ...................................................................................... 250
CHAPTER 8 Microscopic Analysis
8.1 Introduction ............................................................................................. 253
8.2 Preparation of the Samples .................................................................... 254
8.2.1 Interest.............................................................................................. 254
8.2.2 Coating and Impregnation, Thin Sections ......................................... 255
8.2.3 Grids and Replicas for Transmission Electron Microscopy ............... 261
8.2.4 Mounting the Samples for Scanning Electron Microscopy ................ 263
8.2.5 Surface Treatment (Shadowing, Flash-carbon, Metallization) .......... 265
9. X Contents
8.3 Microscope Studies................................................................................. 267
8.3.1 Optical Microscopy ........................................................................... 267
8.3.2 Electron Microscopy, General Information ........................................ 270
8.3.3 Transmission Electron Microscopy, Micro-diffraction ........................ 271
8.3.4 Scanning Electron Microscopy.......................................................... 279
8.3.5 Ultimate Micro-analysis by X-Ray Spectrometry............................... 282
References ..................................................................................................... 283
Chronobibliography ...................................................................................... 284
PART 2 - ORGANIC ANALYSIS
CHAPTER 9 Physical Fractionation of Organic Matter
9.1 Principle and Limitations ........................................................................289
9.1.1 Forms of Organic Matter in Soil .........................................................289
9.1.2 Principle.............................................................................................289
9.1.3 Difficulties ..........................................................................................291
9.2 Methods ....................................................................................................293
9.2.1 Classification .....................................................................................293
9.2.2 Extraction of Plant Roots ...................................................................293
9.2.3 Dispersion of the Particles.................................................................296
9.2.4 Separation by Density. ......................................................................309
9.2.5 Particle Size Fractionations ...............................................................314
9.2.6 Precision of the Fractionation Methods .............................................320
9.3 Conclusion and Outlook..........................................................................321
References......................................................................................................322
CHAPTER 10 Organic and Total C, N (H, O, S) Analysis
10.1 Introduction ............................................................................................327
10.1.1 Soil Organic Matter..........................................................................327
10.1.2 Sampling, Preparation of the Samples, Analytical Significance.......330
10.2 Wet Methods...........................................................................................333
10.2.1 Total Carbon: General Information ..................................................333
10.2.2 Organic Carbon by Wet Oxidation at the Temperature
of Reaction ......................................................................................335
10.2.3 Organic Carbon by Wet Oxidation at Controlled Temperature ........340
10.2.4 Organic Carbon by Wet Oxidation and Spectrocolorimetry..............342
10.2.5 Total Nitrogen by Wet Method: Introduction ........ ............................342
10.2.6 Total Nitrogen by Kjeldahl Method and Titrimetry ...........................344
10.2.7 Kjeldahl N, Titration by Spectrocolorimetry......................................349
10.2.8 Kjeldahl N, Titration by Selective Electrode . ....... ............................351
10.2.9 Mechanization and Automation of the Kjeldahl Method...................353
10.2.10 Modified Procedures for NO3–, NO2– and Fixed N .........................354
10.3 Dry Methods ...........................................................................................355
10.3.1 Total Carbon by Simple Volatilization ..............................................355
10.3.2 Simultaneous Instrumental Analysis by Dry Combustion: CHN(OS)356
10.3.3 CHNOS by Thermal Analysis ..........................................................362
10. Contents XI
10.3.4 C and N Non-Destructive Instrumental Analysis..............................363
10.3.5 Simultaneous Analysis of the Different C and N Isotopes ...............364
References......................................................................................................365
Bibliography ...................................................................................................367
CHAPTER 11 Quantification of Humic Compounds
11.1 Humus in Soils .......................................................................................371
11.1.1 Definitions........................................................................................371
11.1.2 Role in the Soil and Environment ....................................................373
11.1.3 Extractions.......................................................................................374
11.2 Main Techniques ....................................................................................375
11.2.1 Extraction ........................................................................................375
11.2.2 Quantification of the Extracts...........................................................379
11.2.3 Precision and Correspondence of the Extraction Methods ............. 383
11.2.4 Purification of Humic Materials ....................................................... 389
11.3 Further Alternatives and Complements Methods............................... 392
11.3.1 Alternative Method of Extraction ..................................................... 392
11.3.2 Fractionation of the Humin Residue................................................ 392
References ..................................................................................................... 395
Humic Materials ......................................................................................... 395
Extraction, Titration, Purification and Fractionation of Humic Materials ..... 396
CHAPTER 12 Characterization of Humic Compounds
12.1 Introduction ........................................................................................... 399
12.1.1 Mechanisms of Formation............................................................... 399
12.1.2 Molecular Structure......................................................................... 400
12.2. Classical Techniques ........................................................................... 401
12.2.1 Fractionation of Humic Compounds................................................ 401
12.2.2 Titration of the Main Functional Groups .......................................... 408
12.2.3 UV–Visible Spectrometry ................................................................ 410
12.2.4 Infra-Red Spectrography................................................................. 413
12.3 Complementary Techniques ................................................................ 415
12.3.1 Improvements in Fractionation Technologies ................................. 415
12.3.2 Titration of Functional Groups......................................................... 418
12.3.3 Characterization by Fragmentation ................................................. 419
12.3.4 Nuclear Magnetic Resonance (NMR) ............................................. 424
12.3.5 Fluorescence Spectroscopy............................................................ 433
12.3.6 Electron Spin Resonance (ESR) Spectroscopy .............................. 435
12.3.7 Measurement of Molecular Weight and Molecular Size ................. 437
12.3.8 Microscopic Observations............................................................... 440
12.3.9 Other Techniques ........................................................................... 441
References ..................................................................................................... 442
Molecular Models....................................................................................... 442
Fractionation, Determination of Molecular Weights and Molecular Sizes .. 443
Functional Group of Humic Compounds .................................................... 445
Spectrometric Characterizations................................................................ 446
UV–Visible, IR, Fluorescence, ESR Spectrometries .................................. 446
Nuclear Magnetic Resonance.................................................................... 447
11. XII Contents
Methods of Characterization by Fragmentation ......................................... 449
Other Methods (Microscopy, X-ray, Electrochemistry, etc.) ...................... 451
CHAPTER 13 Measurement of Non-Humic Molecules
13.1 Introduction ........................................................................................... 453
13.1.1 Non-Humic Molecules..................................................................... 453
13.1.2 Soil Carbohydrates ......................................................................... 453
13.1.3 Soil Lipids ....................................................................................... 456
13.1.4 Pesticides and Pollutants................................................................ 457
13.2 Classical Techniques ............................................................................ 458
13.2.1 Acid Hydrolysis of Polysaccharides ................................................ 458
13.2.2 Purification of Acid Hydrolysates .................................................... 462
13.2.3 Colorimetric Titration of Sugars ...................................................... 464
13.2.4 Titration of Sugars by Gas Chromatography................................... 467
13.2.5 Quantification of Total Lipids........................................................... 472
13.2.6 Quantification of the Water-Soluble Organics ................................. 474
13.3 Complementary Techniques .................................................................475
13.3.1 Carbohydrates by Gas Chromatography..........................................475
13.3.2 Carbohydrates by Liquid Chromatography ......................................475
13.3.3 Fractionation and Study of the Soil Lipid Fraction ...........................478
13.3.4 Measurement of Pesticide Residues and Pollutants .......................483
References......................................................................................................492
Soil Carbohydrates..................................................................................... 492
Soil Lipids .................................................................................................. 494
Aqueous Extract ........................................................................................ 495
Pesticides and Pollutants........................................................................... 495
CHAPTER 14 Organic Forms of Nitrogen, Mineralizable Nitrogen
(and Carbon)
14.1 Introduction ............................................................................................497
14.1.1 The Nitrogen Cycle..........................................................................497
14.1.2 Types of Methods ............................................................................499
14.2 Classical Methods..................................................................................500
14.2.1 Forms of Organic Nitrogen Released by Acid Hydrolysis ................500
14.2.2 Organic Forms of Nitrogen: Simplified Method ................................509
14.2.3 Urea Titration ...................................................................................511
14.2.4 Potentially Available Nitrogen: Biological Methods ..........................513
14.2.5 Potentially Mineralizable Nitrogen: Chemical Methods....................521
14.2.6 Kinetics of Mineralization.................................................................526
14.3 Complementary Methods ......................................................................531
14.3.1 Alternative Procedures for Acid Hydrolysis......................................531
14.3.2 Determination of Amino Acids .........................................................532
14.3.3 Determination of Amino Sugars .......................................................535
14.3.4 Proteins and Glycoproteins (glomalin).............................................538
14.3.5 Potentially Mineralizable Nitrogen by EUF ......................................538
12. Contents XIII
References ......................................................................................................540
Organic Nitrogen Forms: General Articles ..................................................540
Nitrogen Forms by Acid Hydrolysis and Distillation ....................................541
Improvement of Acid Hydrolysis .................................................................541
Determination of Amino Acids ....................................................................541
Determination of Amino Sugars..................................................................542
Glomalin .....................................................................................................542
Urea Titration..............................................................................................543
Potentially Mineralizable Nitrogen: General Papers ...................................543
Potentially Mineralizable Nitrogen: Biological Methods ..............................544
Potentially Mineralizable Nitrogen: Chemical Methods...............................545
Potentially Mineralizable Nitrogen by EUF .................................................545
Mineralization Kinetics ...............................................................................546
PART 3 - INORGANIC ANALYSIS – Exchangeable and Total Elements
CHAPTER 15 pH Measurement
15.1 Introduction ........................................................................................... 551
15.1.1 Soil pH ............................................................................................ 551
15.1.2 Difficulties ....................................................................................... 553
15.1.3 Theoretical Aspects ........................................................................ 554
15.2 Classical Measurements....................................................................... 556
15.2.1 Methods .......................................................................................... 556
15.2.2 Colorimetric Method........................................................................ 557
15.2.3 Electrometric Method ...................................................................... 560
15.2.4 Electrometric Checking and Calibration .......................................... 564
15.2.5 Measurement on Aqueous Soil Suspensions ................................. 565
15.2.6 Determination of the pH-K and pH-Ca ............................................ 567
15.2.7 Measurement on Saturated Pastes ................................................ 567
15.2.8 Measurement on the Saturation Extract.......................................... 568
15.2.9 Measurement of the pH-NaF .......................................................... 569
15.3 In Situ Measurements ........................................................................... 570
15.3.1 Equipment....................................................................................... 570
15.3.2 Installation in the Field .................................................................... 570
15.3.3 Measurement on Soil Monoliths...................................................... 572
References ..................................................................................................... 574
Bibliography .................................................................................................. 575
Appendix ........................................................................................................ 576
Appendix 1: Table of Electrode Potentials ................................................. 576
Appendix 2: Constants of Dissociation of Certain Equilibriums.................. 577
Appendix 3: Buffer Solutions...................................................................... 577
Appendix 4: Coloured Indicators................................................................ 579
CHAPTER 16 Redox Potential
16.1 Definitions and Principle ...................................................................... 581
16.2 Equipment and Reagents ..................................................................... 583
16.2.1 Electrodes....................................................................................... 583
16.2.2 Salt Bridge for Connection .............................................................. 584
16.2.3 System of Measurement ................................................................. 584
16.2.4 Calibration Solutions ....................................................................... 585
13. XIV Contents
16.3 Procedure............................................................................................... 585
16.3.1 Pretreatment of the Electrode ......................................................... 585
16.3.2 Measurement on Soil Sample......................................................... 586
16.3.3 Measurement on Soil Monolith ....................................................... 586
16.3.4 In Situ Measurements..................................................................... 587
16.3.5 Measurement of Oxygen Diffusion Rate ......................................... 588
16.3.6 Colorimetric Test of Eh ................................................................... 589
References ..................................................................................................... 589
Bibliography .................................................................................................. 590
CHAPTER 17 Carbonates
17.1 Introduction ........................................................................................... 593
17.2 Measurement of Total Carbonates....................................................... 595
17.2.1 Introduction ..................................................................................... 595
17.2.2 Volumetric Measurement by Calcimetry ..........................................596
17.2.3 Acidimetry........................................................................................599
17.3 Titration of Active Carbonate ................................................................601
17.3.1 Principle...........................................................................................601
17.3.2 Implementation ................................................................................601
17.3.3 Index of Chlorosis Potential.............................................................603
References......................................................................................................604
CHAPTER 18 Soluble Salts
18.1 Introduction ............................................................................................605
18.2 Extraction ...............................................................................................606
18.2.1 Soil/solution Ratio............................................................................606
18.2.2 Extraction of Saturated Paste..........................................................607
18.2.3 Diluted Extracts ...............................................................................608
18.2.4 In Situ Sampling of the Soil Water ...................................................609
18.2.5 Extracts with Hot Water ...................................................................610
18.3 Measurement and Titration ...................................................................610
18.3.1 Electrical Conductivity of Extracts....................................................610
18.3.2 In Situ Conductivity..........................................................................613
18.3.3 Total Dissolved Solid Material .........................................................614
18.3.4 Soluble Cations ...............................................................................615
18.3.5 Extractable Carbonate and Bicarbonate (Alkalinity) ........................616
18.3.6 Extractable Chloride ........................................................................618
18.3.7 Extractable Sulphate, Nitrate and Phosphate ..................................620
18.3.7 Extractable Boron ............................................................................620
18.3.8 Titration of Extractable Anions by Ionic Chromatography................622
18.3.9 Expression of the Results................................................................625
References......................................................................................................626
CHAPTER 19 Exchange Complex
19.1 Introduction ............................................................................................629
19.2 Origin of Charges...................................................................................630
19.2.1 Ionic Exchange ................................................................................630
14. Contents XV
19.2.2 Exchange Complex .........................................................................631
19.2.3 Theory .............................................................................................633
References......................................................................................................636
Chronobibliography.......................................................................................637
CHAPTER 20 Isoelectric and Zero Charge Points
20.1 Introduction ............................................................................................645
20.1.1 Charges of Colloids .........................................................................645
20.1.2 Definitions........................................................................................647
20.1.3 Conditions for the Measurement of Charge.....................................649
20.2 Main Methods .........................................................................................651
20.2.1 Measurement of pH0 (PZSE), Long Equilibrium Time .....................651
20.2.2 Point of Zero Salt Effect (PZSE), Short Equilibrium Time ................652
References......................................................................................................655
CHAPTER 21 Permanent and Variable Charges
21.1 Introduction ........................................................................................... 657
21.2 Main Methods......................................................................................... 661
21.2.1 Measurement of Variable Charges ................................................. 661
21.2.2 Determination of Permanent Charges............................................. 662
References ..................................................................................................... 664
Bibliography .................................................................................................. 665
CHAPTER 22 Exchangeable Cations
22.1 Introduction ........................................................................................... 667
22.1.1 Exchangeable Cations of Soil ......................................................... 667
22.1.2 Extracting Reagents........................................................................ 668
22.1.3 Equipment....................................................................................... 669
22.2 Ammonium Acetate Method at pH 7 .................................................... 671
22.2.1 Principle .......................................................................................... 671
22.2.2 Procedure ....................................................................................... 671
22.3 Automated Continuous Extraction ...................................................... 674
References ..................................................................................................... 674
Bibliography .................................................................................................. 676
CHAPTER 23 Exchangeable Acidity
23.1 Introduction ........................................................................................... 677
23.1.1 Origin of Acidity............................................................................... 677
23.1.2 Aims of the Analysis........................................................................ 678
23.2 Method.................................................................................................... 680
23.2.1 Principle .......................................................................................... 680
23.2.2 Reagents ........................................................................................ 680
23.2.3 Procedure ....................................................................................... 681
23.3 Other Methods ....................................................................................... 683
References ..................................................................................................... 684
Chronobibliography ...................................................................................... 685
15. XVI Contents
CHAPTER 24 Lime Requirement
24.1 Introduction ........................................................................................... 687
24.1.1 Correction of Soil Acidity................................................................. 687
24.1.2 Calculation of Correction................................................................. 688
24.2 SMP Buffer Method ............................................................................... 690
24.2.1 Principle .......................................................................................... 690
24.2.2 Reagents ........................................................................................ 691
24.2.3 Procedure ....................................................................................... 691
24.2.4 Remarks ......................................................................................... 692
References ..................................................................................................... 693
Chronobibliography ...................................................................................... 693
CHAPTER 25 Exchange Selectivity, Cation Exchange Isotherm
25.1 Introduction ........................................................................................... 697
25.2 Determination of the Exchange Isotherm............................................ 702
25.2.1 Principle .......................................................................................... 702
25.2.2 Reagents ........................................................................................ 702
25.2.3 Procedure........................................................................................703
25.2.4 Remarks ..........................................................................................704
References......................................................................................................705
Chronobibliography.......................................................................................706
CHAPTER 26 Cation Exchange Capacity
26.1 Introduction ............................................................................................709
26.1.1 Theoretical Aspects .........................................................................709
26.1.2 Variables that Influence the Determination of CEC..........................711
26.2 Determination of Effective CEC by Summation (ECEC) .....................718
26.2.1 Principle...........................................................................................718
26.2.2 Alternative Methods.........................................................................718
26.3 CEC Measurement at Soil pH in Not-Buffered Medium .....................719
26.3.1 Principle...........................................................................................719
26.3.2 Methods Using Not-Buffered Metallic Salts .....................................719
26.3.3 Procedure Using Not-Buffered Organo Metallic Cations .................722
26.3.4 Not-Buffered Methods Using Organic Cations ................................ 728
26.4 CEC Measurement in Buffered Medium ...............................................730
26.4.1 Buffered Methods — General Information .......................................730
26.4.2 Ammonium Acetate Method at pH 7.0.............................................732
26.4.3 Buffered Methods at pH 8.0–8.6......................................................738
26.4.4 Buffered Methods at Different pH ....................................................743
References......................................................................................................745
Bibliography ...................................................................................................750
CEC General Theory ..................................................................................750
Barium Method at soil pH ...........................................................................751
Buffered Method at pH 7.0 .........................................................................751
Cobaltihexamine CEC ................................................................................752
Silver-Thiourea ...........................................................................................753
CEC with Organic Cations (Coloured Reagents) ....................................... 753
Buffered Methods at pH 8.0–8.6.................................................................753
Barium Chloride-Triethanolamine at pH 8.1 ............................................... 753
16. Contents XVII
CHAPTER 27 Anion Exchange Capacity
27.1 Theory .....................................................................................................755
27.2 Measurement ..........................................................................................758
27.2.1 Principle...........................................................................................758
27.2.2 Method ............................................................................................760
27.3 Simultaneous Measurement of AEC, EC, CEC and net CEC ..............760
27.3.1 Aim ..................................................................................................760
27.3.2 Description ......................................................................................761
References......................................................................................................763
CHAPTER 28 Inorganic Forms of Nitrogen
28.1 Introduction ............................................................................................767
28.1.1 Ammonium, Nitrate and Nitrite ........................................................767
28.1.3 Sampling Problems .........................................................................768
28.1.4 Analytical Problems .........................................................................768
28.2 Usual Methods .......................................................................................769
28.2.1 Extraction of Exchangeable Forms..................................................769
28.2.2 Separation by Micro-Diffusion......................................................... 770
28.2.3 Colorimetric Titration of Ammonium................................................ 773
28.2.4 Colorimetric Titration of Nitrites....................................................... 775
28.2.5 Colorimetric Titration of Nitrates ..................................................... 778
28.2.6 Extracted Organic Nitrogen............................................................. 779
28.3 Other Methods ....................................................................................... 780
28.3.1 Nitrate and Nitrite by Photometric UV Absorption ........................... 780
28.3.2 Ammonium Titration Using a Selective Electrode ........................... 782
28.3.3 Measurement of Nitrates with an Ion-Selective Electrode............... 785
28.3.4 In situ Measurement ....................................................................... 788
28.3.5 Non-Exchangeable Ammonium ...................................................... 790
References ..................................................................................................... 791
Bibliography .................................................................................................. 792
CHAPTER 29 Phosphorus
29.1 Introduction ........................................................................................... 793
29.2 Total Soil Phosphorus .......................................................................... 794
29.2.1 Introduction ..................................................................................... 794
29.2.2 Wet Mineralization for Total Analyses............................................. 795
29.2.3 Dry Mineralization ........................................................................... 798
29.3 Fractionation of Different Forms of Phosphorus................................ 799
29.3.1 Introduction ..................................................................................... 799
29.3.2 Sequential Methods ........................................................................ 800
29.3.3 Selective Extractions – Availability Indices ..................................... 804
29.3.4 Isotopic Dilution Methods................................................................ 813
29.3.5 Determination of Organic Phosphorus ............................................ 814
29.4 Retention of Phosphorus...................................................................... 818
29.4.1 Introduction ..................................................................................... 818
29.4.2 Determination of P Retention.......................................................... 819
17. XVIII Contents
29.5 Titration of P in the Extracts................................................................. 821
29.5.1 Introduction ..................................................................................... 821
29.5.2 Titration of Ortho-phosphoric P by Spectrocolorimetry ................... 823
29.5.3 P Titration by Atomic Spectrometry . ............................................... 828
31
29.5.4 Titration of Different Forms of P by P NMR .................................. 828
29.5.5 Separation of P Compounds by Liquid Chromatography ................ 829
29.6 Direct Speciation of P in situ, or on Extracted Particles .................... 830
References ..................................................................................................... 830
Chronobibliography ...................................................................................... 833
CHAPTER 30 Sulphur
30.1 Introduction ........................................................................................... 835
30.1.1 Sulphur Compounds ....................................................................... 835
30.1.2 Mineralogical Studies...................................................................... 838
30.2 Total Sulphur and Sulphur Compounds .............................................. 839
30.2.1 Characteristics of Fluviomarine Soils .............................................. 839
30.2.2 Soil Sampling and Sample Preparation .......................................... 840
30.2.3 Testing for Soluble Sulphur Forms ................................................. 841
30.2.4 Titration of Total Sulphur................................................................. 842
30.2.5 Total S Solubilisation by Alkaline Oxidizing Fusion......................... 843
30.2.6 Total Solubilisation by Sodium Hypobromite in Alkaline Medium.... 844
30.2.7 S titration with Methylen Blue Colorimetry ...................................... 845
30.2.8 Sulphate Titration by Colorimetry with Methyl Thymol Blue............. 850
30.2.9 Total Sulphur by Automated Dry CHN(OS) Ultimate Analysis ......... 853
2–
30.2.10 Titration of Total SO4 -S by Ionic Chromatography ...................... 855
30.2.11 Total S Titration by Plasma Emission Spectrometry...................... 857
30.2.12 Titration by X-ray Fluorescence..................................................... 857
30.2.13 Titration by Atomic Absorption Spectrometry ................................ 857
30.2.14 Analytical Fractionation of Sulphur Compounds ............................ 858
30.2.15 Titration of Organic S bound to C .................................................. 859
30.2.16 Titration of Organic S not bound to C ............................................ 861
30.2.17 Extraction and Titration of Soluble Sulphides ................................ 863
30.2.18 Titration of Sulphur in Pyrites ........................................................ 865
30.2.19 Titration of Elementary Sulphur ..................................................... 867
30.2.20 Titration of Water Soluble Sulphates ............................................. 869
30.2.21 Titration of Na3-EDTA Extractable Sulphates ................................ 871
30.2.22 Titration of Jarosite ........................................................................ 873
30.2.23 Sequential Analysis of S Forms..................................................... 876
30.3 Sulphur of Gypseous Soils ................................................................... 878
30.3.1 Gypseous Soils ............................................................................... 878
30.3.2 Preliminary Tests............................................................................. 879
30.3.3 Extraction and Titration from Multiple Extracts ................................ 881
30.3.4 Gypsum Determination by Acetone Precipitation ............................ 882
30.4 Sulphur and Gypsum Requirement of Soil .......................................... 883
30.4.1 Introduction...................................................................................... 883
30.4.2 Plant Sulphur Requirement ............................................................. 884
30.4.3 Gypsum Requirement...................................................................... 886
References...................................................................................................... 888
Chronobibliography....................................................................................... 890
18. Contents XIX
CHAPTER 31 Analysis of Extractable and Total Elements
31.1 Elements of Soils ...................................................................................895
31.1.1 Major Elements ...............................................................................895
31.1.2 Trace Elements and Pollutants........................................................897
31.1.3 Biogenic and Toxic Elements ..........................................................899
31.1.4 Analysis of Total Elements ..............................................................900
31.1.5 Extractable Elements.......................................................................901
31.2 Methods using Solubilization................................................................901
31.2.1 Total Solubilization Methods............................................................901
31.2.2 Mean Reagents for Complete Dissolutions .....................................903
31.2.3 Acid Attack in Open Vessel .............................................................906
31.2.4 Acid Attack in Closed Vessel...........................................................911
31.2.5 Microwave Mineralization ................................................................913
31.2.6 Alkaline Fusion ................................................................................915
31.2.7 Selective Extractions .......................................................................920
31.2.8 Measurement Methods....................................................................925
31.2.9 Spectrocolorimetric Analysis ............................................................927
31.2.10 Analysis by Flame Atomic Emission Spectrometry........................931
31.2.11 Analysis by Flame Atomic Absorption Spectrometry .....................932
31.2.12 Analysis of Trace Elements by Hydride and Cold Vapour AAS .....937
31.2.13 Analysis of Trace Elements by Electrothermal AAS ......................940
31.2.14 Analysis by Inductively Coupled Plasma-AES ..............................941
31.2.15 Analysis by Inductively Coupled Plasma-Mass Spectrometry .......946
31.3 Analysis on Solid Medium ....................................................................952
31.3.1 Method ............................................................................................952
31.3.2 X-ray Fluorescence Analysis ........................................................... 954
31.3.3 Neutron Activation Analysis ............................................................962
References .....................................................................................................969
INDEX ...................………………………………………………………………….975
PERIODIC TABLE OF THE ELEMENTS ....................................................... 993
20. 1
Water Content and Loss on Ignition
1.1 Introduction
Schematically, a soil is made up of a solid, mineral and organic phase, a
liquid phase and a gas phase. The physical and chemical characteristics of
the solid phase result in both marked variability of water contents and a
varying degree of resistance to the elimination of moisture.
For all soil analytical studies, the analyst must know the exact quantity
of the solid phase in order to transcribe his results in a stable and
reproducible form. The liquid phase must be separate, and this operation
must not modify the solid matrix significantly (structural water is related
to the crystal lattice).
Many definitions exist for the terms “moisture” and “dry soil”. The
water that is eliminated by moderate heating, or extracted using solvents,
represents only one part of total moisture, known as hygroscopic water,
which is composed of (1) the water of adsorption retained on the surface
of solids by physical absorption (forces of van der Waals), or by
chemisorption, (2) the water of capillarity and swelling and (3) the
hygrometrical water of the gas fraction of the soil (ratio of the effective
pressure of the water vapour to maximum pressure). The limits between
these different types of water are not strict.
“Air-dried” soil, which is used as the reference for soil preparation in
the laboratory, contains varying amounts of water which depend in
particular on the nature of secondary minerals, but also on external forces
(temperature, the relative humidity of the air). Some andisols or histosols
that are air dried for a period of 6 months can still contain 60% of water
in comparison with soils dried at 105°C, and this can lead to unacceptable
errors if the analytical results are not compared with a more realistic
21. 4 Mineralogical Analysis
reference for moisture.1 Saline soils can also cause problems because of
the presence of hygroscopic salts.
It is possible to determine remarkable water contents involving fields of
force of retention that are sufficiently reproducible and representative
(Table 1.1). These values can be represented in the form of capillary
potential (pF), the decimal logarithm of the pressure in millibars needed
to bring a sample to a given water content (Table 1.1). It should be noted
that because of the forces of van der Waals, there can be differences in
state, but not in form, between water likely to evaporate at 20°C and
water that does not freeze at –78°C. The analyst defines remarkable
points for example:
– The water holding capacity, water content where the pressure
component of the total potential becomes more significant than the
gravitating component; this depends on the texture and the nature of the
mineral and approaches field capacity which, after suitable drainage,
corresponds to a null gravitating flow.
– The capillary frangible point, a state of moisture where the continuous
water film becomes monomolecular and breaks.
– The points of temporary and permanent wilting where the pellicular
water retained by the bonding strength balances with osmotic pressure;
in this case, except for some halophilous plants, the majority of plants
can no longer absorb the water that may still be present in the soil.
– The hygroscopic water which cannot be easily eliminated in the natural
environment as this requires considerable energy, hygroscopic water
evaporates at temperatures above 100°C and does not freeze at –78°C.
– The water of constitution and hydration of the mineral molecules can
only be eliminated at very high pressures or at high temperatures, with
irreversible modification or destruction of the crystal lattice.
These types of water are estimated using different types of
measurements to study the water dynamics and the mechanisms related to
the mechanical properties of soils in agronomy and agricultural
engineering, for example:
– usable reserves (UR), easily usable reserves (EUR), or reserves that are
easily available in soil–water–plant relations.
– thresholds of plasticity, adhesiveness, liquidity (limits of Atterberg,
etc.).
1 It should be noted that for these types of soil, errors are still amplified by the
ponderal expression (because of an apparent density that is able to reach 0.3)
this is likely to make the analytical results unsuitable for agronomic studies.
22. Table 1.1 -
Approximate
correspondence
moistures –
pressure –
diameter of the
Water Content and Loss on Ignition
pores – types of
water and critical
points in soils with
respect to plant
requirements
5
23. 6 Mineralogical Analysis
This brief summary gives an indication of the complexity of the
concept of soil moisture and the difficulty for the analyst to find a
scientifically defined basis for dry soil where the balance of the solid,
liquid and gas phases is constant.
1.2 Water Content at 105°C (H2 O −)
1.2.1 Principle
By convention, the term “moisture” is considered to be unequivocal.
Measurement is carried out by gravimetry after drying at a maximum
temperature of 105°C. This increase in temperature maintained for a
controlled period of time, is sufficiently high to eliminate “free” forms of
water and sufficiently low not to cause a significant loss of organic matter
and unstable salts by volatilization. Repeatability and reproducibility are
satisfactory in the majority of soils if procedures are rigorously respected.
1.2.2 Materials
– 50 × 30 mm borosilicate glass low form weighing bottle with ground
flat top cap.
– Vacuum type Ø 200 mm desiccator made of borosilicate glass with
removable porcelain floor, filled with anhydrous magnesium
perchlorate [Mg(ClO4)2].
– Thermostatically controlled drying oven with constant speed blower for
air circulation and exhausting through a vent in the top of oven –
temperature uniformity ± 0.5–1°C.
– Analytical balance: precision 0.1 mg, range 100 g.
1.2.3 Sample
It is essential to measure water content on the same batch of samples
prepared at the same time (fine earth with 2 mm particles or ground soil)
for subsequent analyses. It should be noted that the moisture content of
the prepared soil may change during storage (fluctuations in air moisture
and temperature, oxidation of organic matter, loss or fixing of volatile
substances, etc.).
24. Water Content and Loss on Ignition 7
This method can be considered “destructive” for certain types of soils
and analyses, as the physical and chemical properties can be transformed.
Samples dried at 105°C should generally not be used for other
measurements.
1.2.4 Procedure
– Dry tared weighing bottles for 2 h at 105°C, let them cool in the
desiccator and weigh the tare with the lid placed underneath: m0
– Place about 5 g of air-dried soil (fine earth sieved through a 2 mm
mesh) in the tare box and note the new weight: m1
– Place the weighing bottles with their flat caps placed underneath in a
ventilated drying oven for 4 h at 105°C (the air exit must be open and
the drying oven should not be overloaded)
– Cool in the desiccator and weigh (all the lids of the series contained in
the desiccator should be closed to avoid moisture input): m2
– Again place the opened weighing bottles in the drying oven for 1 h at
105°C and weigh under the same conditions; the weight should be
constant; if not, continue drying the weighing bottles until their weight
is constant
m1 − m2
% water content at 105°C = 100 × .
m1 − m0
1.2.5 Remarks
The results can also be expressed in pedological terms of water holding
capacity (HC) by the soil: HC = 100 × m1 − m2 .
m 2 − m0
The point of measurement at 105°C with constant mass is empirical
(Fig. 1.1). A temperature of 130°C makes it possible to release almost all
“interstitial water”, but this occurs to the detriment of the stability of
organic matter. The speed of drying should be a function of the
temperature, the surface of diffusion, the division of the solid, ventilation,
pressure (vacuum), etc.
Respecting the procedure is thus essential:
– For andisols and histosols, the initial weighing should be systematically
carried out after 6 h.
– For saline soils with large quantities of dissolved salts, the sample can
be dried directly, soluble salts then being integrated into the “dry soil”
or eliminated beforehand by treatment with water.
25. 8 Mineralogical Analysis
Fig. 1.1 - Theoretical
diagrammatic curve
showing water moved at
a given temperature as a
function of time (180°C =
end of H2O losses in
allophanes)
1.3 Loss on Ignition at 1,000°C (H2O +)
1.3.1 Introduction
As we have just seen, the reference temperature (105°C) selected for the
determination of the moisture content of a “dry soil” represents only _ a
totally hypothetical state of the water that is normally referred to as H2O .
When a sample undergoes controlled heating and the uninterrupted
ponderal variations are measured, curves of “dehydration” are obtained
whose inflections characterize losses in mass at certain critical
temperatures (TGA).1 If one observes the temperature curve compared to
a thermically inert substance (Fig. 1.2), it is possible to determine
changes in energy between the sample studied and the reference
substance, this results in a change in the temperature which can be
measured (DTA–DSC).2
– If the temperature decreases compared to the reference, an endothermic _
peak appears that characterizes loss of H2O (dehydration), of OH
(dehydroxylation), sublimation, or evaporation, or decomposition of
certain substances, etc.
– If the temperature increases compared to the reference, an exothermic
peak appears that characterizes transformations of crystalline structures,
oxidations (Fe2+ → Fe3+), etc.
2 TGA thermogravimetric analysis; DTA differential thermal analysis; DSA
differential scanning calorimetry (cf. Chap. 7).
26. Water Content and Loss on Ignition 9
Fig. 1.2 - Schematized
example of thermal
analysis curves
TGA (solid line) and
DTA (dashed line)
The simultaneous analysis of the gases or vapours that are emitted and
X-ray diffraction (cf. Chap. 4) of the modifications in structure make it
possible to validate the inflections of the curves or the different endo- and
exothermic peaks.
As can be seen in the highly simplified Table 1.2, the most commonly
observed clays are completely dehydroxyled at 1,000°C, oxides at 400°C
or 500°C, carbonates, halogens, sulphates, sulphides are broken down or
dehydrated between 300°C and 1,000°C, and free or bound organic
matter between 300°C and 500°C. The temperature of 1,000°C can thus
be retained as a stable reference temperature for loss on ignition, the
thermal spectra then being practically flat up to the peaks of fusion which
generally only appear at temperatures higher than 1,500°C or even
2,500°C.
1.3.2 Principle
The sample should be gradually heated in oxidizing medium to 1,000°C
and maintained at this temperature for 4 h.
27. 10 Mineralogical Analysis
Table 1.2 Dehydration and dehydroxylation of some clays, oxides and
salts as a function of temperature in °C
type name dehydrationa dehydroxylationb
clays 1:1 Kaolinite–halloysite 350 1,000
clays 2:1 smectites – 370 1,000
montmorillonite
clays 2:1 Illite – micas 350–370 1,000
clays 2:1 vermiculite 700 1,000
clays 2:1:1 chlorite 600 800
fibrous clays Sepiolite– 300 800–900
palygorskite 200 900–1,000
allophane
iron oxides Hematite α Fe2O3 (flat 1,000
spectrum)
goethite α FeO–OH 100 370
magnetite Fe2O3 375 650
Al oxides gibbsite γ-Al(OH)3 100 350
Ca carbonate Calcite–aragonite – 950–1,000
CaCO3
Mg carbonate magnesite MgCO3 – 710
Ca–Mg dolomie – 800–940
carbonate CaMg(CO3)2
halogenous sodium chloride – 800 (fusion)
compounds NaCl
sulphate gypsum CaSO4, – 300
2H2O
sulphide pyrite FeS2 – 615
organic free or linked organic – 300–500
compounds matter
a Dehydration: loss of water adsorbed on outer or inner surfaces, with
or without reversible change in the lattice depending on the types of
clay, water organized in monomolecular film on surface oxygen
atoms or around exchangeable cations.
b dehydroxylation (+ decarbonatation and desulphurization reactions),
loss of water linked to lattice (OH−), irreversible reaction or
destruction of the structure, water present in the cavities, O forming
the base of the tetrahedrons.
28. Water Content and Loss on Ignition 11
Loss on ignition is determined by gravimetry. It includes combined
water linked to the crystal lattice plus a little residual non-structural
adsorbed water, organic matter, possibly volatile soluble salts (F−, S2−)
and carbonates (CO32−, CO2). The use of an oxidizing atmosphere is
essential to ensure combustion of the organic matter and in particular
oxidation of reduced forms of iron, this being accompanied by an
increase in mass of the soils with minerals rich in Fe2+. A complete
analysis generally includes successive measurements of H2O− and H2O+
on the same sample.
1.3.3 Equipment
– Platinum or Inconel (Ni–Cr–Fe) crucible with cover, diameter 46 mm.
– Analytical balances (id. H2O−)
– Desiccator (id. H2O−)
– Muffle electric furnace (range 100–1,100°C) with proportional
electronic regulation allowing modulation of the impulses with
oscillation of about 1°C around the point of instruction; built-in
ventilation system for evacuation of smoke and vapour
– Thermal protective gloves
– 300 mm crucible tong
1.3.4 Procedure
– Tare a crucible, heat it to 1,000°C and cool it in the desiccator with its
lid on: m0
– Introduce 2–3 g of air-dried soil crushed to 0.1 mm: m1
– Dry in the drying oven at 105°C for 4 h
– Cool in the desiccator and weigh: m2
– Adjust the lid of the crucible so it covers approximately 2/3 of the
crucible and put it in the electric furnace
– Programme a heating gradient of approximately 6°C per minute with a
20-min stage at 300°C, then a fast rise at full power up to 1,000°C with
a 4-h graduation step (the door of the furnace should only be closed
after complete combustion of the organic matter)
– Cool the crucible in the desiccator and weigh: m3
1.3.5 Calculations
m1 – m0 = weight of air-dried soil
m1 – m2 = moisture at 105°C
29. 12 Mineralogical Analysis
m2 – m0 = weight of soil dried at 105°C
m2 – m3 = loss on ignition
m1 − m2
H 2O – % = 100 ×
m1 − m0 related to air-dried soil
+ m2 − m3
H 2O % = 100 ×
m2 − m0 related to soil dried at 105°C
1.3.6 Remarks
Knowing the moisture of the air-dried soil, it is possible to calculate the
weight of air-dried soil required to work with a standard weight soil dried
at 105°C, thus simplifying calculations during analyses of the samples.
To obtain the equivalent of 1 g of soil dried at 105°C, it is necessary to
weigh:
100
with wc = % water content of air dried soil.
100 − wc
Platinum crucibles are very expensive and are somewhat volatile at
1,000°C, which means they have to be tared before each operation,
particularly when operating in reducing conditions.
Combustion of organic matter with insufficient oxygen can lead to the
formation of carbide of Pt, sulphides combine with Pt, chlorine attacks Pt,
etc.
Bibliography
Campbell GS, Anderson RY (1998) Evaluation of simple transmission line
oscillators for soil moisture measurement. Comput. and Electron. Agric.,
20, 31–44
Chin Huat Lim, Jackson ML (1982) Dissolution for total elemental analysis. In
Methods of Soil Analysis, Part 2, Page A.L., Miller R.H., Kenny D.R. ed.
Am. Soc. Agronomy, pp. 1–11
Dixon JB (1977) Minerals in soil environments. Soil Sci. Soc. Am.
Dubois J, Paindavoine JM (1982) Humidité dans les solides, liquides et gaz.
Techniques de l’ingénieur., (P 3760)
Gardner WH (1986) Water content. In Methods of Soil Analysis, Part 1, Klute
ed. Am. Soc. Agronomy, Soil Sci. Soc. Am., pp. 493–544
Henin S (1977) Cours de physique du sol: l'eau et le sol tome II., Editest, Paris:
1–164
Lane PNJ, Mackenzie DH, Nadler AD (2002) Note of clarification about: Field
and laboratory calibration and test of TDR and capacitance techniques for
indirect measurement of soil water content. Aust. J. Soil Res., 40,
555–1386
30. Water Content and Loss on Ignition 13
Lane PNJ, Mackenzie DH (2001) Field and laboratory calibration and test of
TDR and capacitance techniques for indirect measurement of soil. Aust.
J. Soil Res., 39, 1371–1386
NF ISO 11465 (X31-102) (1994) Détermination de la teneur pondérale en
matière sèche et en eau. In Qualité des sols, AFNOR, 1996, 517–524
Rankin LK, Smajstrla AG (1997) Evaluation of the carbide method for soil
moisture measurement in sandy soils. Soil and Crop Science Society of
Florida, 56, pp. 136–139
Skierucha W (2000) Accuracy of soil moisture measurement by TDR technique.
Int. Agrophys., 14, 417–426
Slaughter DC, Pelletier MG, Upadhyaya SK (2001) Sensing soil moisture using
NIR spectroscopy. Appl. Eng. Agric., 17, 241–247
Walker JP, Houser PR (2002) Evaluation of the Ohm Mapper instrument for soil
moisture measurement. Soil Sci. Soc. Am. J., 66, 728–734
X31-505 (1992) Méthode de détermination du volume, apparent, et du contenu
en eau des mottes. In Qualité des sols, AFNOR, 1996, 373–384
Yu C, Warrick AW, Conklin MH (1999) Derived functions of time domain
reflectometry for soil moisture measurement. Water Resour. Res., 35,
1789–1796
31. 2
Particle Size Analysis
2.1 Introduction
2.1.1 Particle Size in Soil Science
Determination of grain-size distribution of a sample of soil is an important
analysis for various topics in pedology, agronomy, sedimentology, and other
fields such as road geotechnics.
Soil texture has an extremely significant influence on the physical and
mechanical behaviours of the soil, and on all the properties related to
water content and the movement of water, (compactness, plasticity, thrust
force, slaking, holding capacity, moisture at different potentials, per-
meability, capillary movements, etc.).
Particle size analysis of a sample of soil, sometimes called “mechanical
analysis”, is a concept that has been the subject of much discussion
(Hénin 1976). Soil is an organized medium including an assemblage of
mineral and organic particles belonging to a continuous dimensional
series. The first difficulty is to express the proportion of these different
particles according to a standard classification, which is consequently
somewhat artificial.
One classification scale was proposed by Atterberg (1912). Today this
scale is recognized at different national and international levels and
includes two main fractions: fine earth (clay, silts and sands with a grain
diameter <2 mm) and coarse elements (gravels, stones with a grain
diameter >2 mm). The particle size series (Fig. 2.1) for fine earth is
generally expressed after analysis in three size fractions (clay fraction
less than 0.002 mm, silt fraction from 0.002 to 0.02 mm, and sand
fraction from 0.02 to 2 mm). In some countries, or for the purpose of a
particular type of pedological interpretation, a more detailed scale of
classes is sometimes used, for example five fractions: fine clays, silts,
coarse silts or very fine sands, fine sands, and coarse sands (Fig. 2.1).
32. 16 Mineralogical Analysis
Fig. 2.1. Ranges of particle size used for soils (NC number of classes; FSi fine
silts, CSi coarse silts; FS, VFS, CS fine, very fine and coarse sands,
respectively; FC fine clays; FG, CG fine gravels and coarse gravels),
from top to bottom: (CSSC) Canadian Soil Survey Committee (1978): 10
particle size ranges < 2 mm; France (before 1987): 8 ranges; USDA
United States Department of Agriculture (1975): 7 ranges; AFNOR
Association Française de Normalisation (1987): 5 ranges; ISSS
= International Soil Science Society (1966): 4 ranges; ASTM = American
Society for Testing Materials (1985): 3 ranges
However, it should be noted that the terminology used does not provide
much information about the real nature of the classes; thus clay defined as
having a diameter equal to or less than 0.002 mm does not contain only
clay corresponding to this mineralogical definition but can also contain
sesquioxides, very fine silts, organic matter, carbonates, or compounds
without colloidal properties. In the same way, sands, which generally result
from fragmentation of the parent rock, can also include pseudo-sands, small
ferruginous concretions, small limestone or cemented nodules that are
resistant to dispersion treatments. The presence of these pseudo-sands can
render the conclusions of particle size analysis illusory.
Another difficulty appears with the fractionation of elementary
particles by dissociating them from their original assembly. Here too
analytical standards exist, but it should be recognized that in certain cases
the rupture of all the forces of cohesion is not complete (the case in
hardened cemented soils), or on the contrary the forces are too energetic.
Lastly, particle size analysis accounts for the size but not for the shape
of the particles, or their nature. If necessary, these are the subject of
33. Particle Size Analysis 17
specific morphoscopic and mineralogical analyses. The result of particle
size analysis is expressed in classes of which the relative proportions can
be summed up in the form of a triangular diagram enabling the texture of
a sample, a horizon, or a soil to be defined. Depending on the school,
there are several different types of triangles that represent textures:
GEPPA (Groupe d’Etude des Problèmes de Pédologie Appliquée, AFES,
Grignon, France) includes 17 textural classes; the USDA’s (United States
Department of Agriculture) includes 12 classes (Gras 1988); others are
simplified to a greater or lesser extent depending on the pedological or
agronomic purpose of the study. Starting from these results, different
interpretations are usually made in terms of pedogenesis (comparison of
the vertical sand percents to check the homogeneity of a given material in
a given soil profile, calculation of different indices of leaching, clay
transport, etc.); others are more practical (definition of the relation of
texture to hydric characteristics for the initial calculation of the amounts
and frequencies of irrigation, or for the choice of machinery for
cultivation.
2.1.2 Principle
Particle size analysis is a laboratory process, which initially causes
dissociation of the material into elementary particles; this implies the
destruction of the aggregates by eliminating the action of cements. But
this action should not be too violent to avoid the creation of particles that
would not naturally exist; the procedure of dispersion must thus be
sufficiently effective to break down the aggregates into individual
components, but not strong enough to create neo-particles.
Measurements (Table 2.1, Fig. 2.2) then will link the size of the
particles to physical characteristics of the suspension of soil after
dispersion (cf. Sect. 2.1.3). These measurements may be distorted by the
presence of some compounds in the soil: organic matter, soluble salts,
sesquioxides, carbonates, or gypsum. The latter compound can be
particularly awkward because it can result in two opposing actions
(Vieillefon 1979): flocculation due to soluble calcium ions (relative
reduction in clay content), and low density of gypsum compared to other
minerals (increase in clay content). Particle size analysis thus generally
starts with a pre-treatment of the sample that varies with the type of soil;
the characteristics of different soils are given in Table 2.3.
34. 18 Mineralogical Analysis
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
– –
–
–
– –
–
–
–
Fig. 2.2. Particle size ranges of some automated particle-measurement instruments
2.1.3 Law of Sedimentation
After possible pretreatment (cf. Sect. 2.2.1), the sample is suspended in
aqueous medium in the presence of a dispersant (cf. Sect. 2.2.2). During
sedimentation, the particles are then subjected to two essential forces: a
force of gravity that attracts them to the bottom, and a force of viscous
resistance of the medium in the opposite direction to their displacement.
By comparing the particles to spheres of radius r, the force of gravity Fg
(dynes) is expressed by:
Fg =
4
3
( )
p r 3 ρs − ρ f g
r = equivalent radius of the spherical particle in cm;
g = gravity constant, 981 cm s–2;
ρs = density of the particles in g cm–3 (between 2.4 and 2.8 for soils);
ρf = density of the liquid of dispersion in g cm–3;
The force of resistance of the medium Fr (dynes) is expressed by:
35. Particle Size Analysis 19
Fr = 6 p r η V ,
V = falling speed in cm s–1;
η = viscosity of the medium in Poises (g cm–1 s–1), at temperature
θ °C (Table 2.2).
When the particles reach equilibrium, the forces Fr and Fr are equal,
from which their drop speed can be estimated according to the law
originally established by Stokes (1851):
2 (ρs −ρf ) g r
2
V= . (2.1)
9η
For calculations, the average density of the solid particles in
dispersions of soils is often selected with ρ S = 2.65 or 2.60 g cm–3.
Empirical relationships have been established for the calculation of ρF
and η in aqueous solutions of hexametaphosphate generally used for
particle-size distribution of soils (Gee and Bauder 1986):
ρt = ρ 0 (1 + 0.630 CHMP), (2.2)
η = η0 (1 + 4.25 CHMP), (2.2’)
ρ0 = density of water (g cm–3 at the working temperature (Table 2.2);
η0 = viscosity of water (poise) at the working temperature (Table 2.2);
CHMP = hexametaphosphate concentration in g cm–3.
The constant of Stokes for the medium can thus be defined by:
C = 2 (ρs – ρf ) g/9 η.
Equation (2.1) shows that the falling speed is proportional to the
square of the particle radius and remains constant throughout
sedimentation if certain conditions are strictly respected (cf. Sect. 2.1.4).
The speed can also be defined by V = h/t where T is the time (s) spent by
the particle of radius r(cm) to fall a height H(cm). Either the depth of its
sedimentation over a given period, or the time needed for sedimentation
to a given depth is determined by:
9 h η −1 −2
t = = h C
( )
r . (2.3)
2
2 ρs − ρ f g r
36. 20
Table 2.1. Systems of particulate characterization for particle size distribution of soils
– destruction of organic matter (H2O2, Na hypochlorite), hypobromite...
individualization
– destruction of cements (Al, Fe, Si): – acid or basic media
of particles
– reducer or complexing media
– in water
2+
desaturation (elimination cations )
chemical acid medium (some andosols)
choice of pH basic medium: NaOH, NH4OH, pyrophosphate, hexametaphosphate
– preliminary treatments various surfactants
suspension
ultrasounds
(dispersion)
physical
mechanical agitation (disintegration: 40 reversals/min)
limiting concentrations
– choice of concentration
wall-attachment effects
separation – techniques used – size phase 1990
principle advantages drawbacks
measurements range recovery firms
measurement by
fragility of sieves,
separation on sieve
mesh defects,
2 mm with vibration with or
measurement of dry mesh obtrusions,
– without ultrasonic
1. sieving etc. Saulas
0.050 yes waves simple
particles wet when dry, fine Tamisor, etc
(5 µm) weighing of the
powders stick to
fractions
coarse ones
(discontinuous)
measurement of
weight of a molecular
film (nitrogen,
EGME...) retained at
2. surface measurement (for internal and
≤ 2 µm no the surface of the difficult to measure micromeritics
memorandum) external surface
particles
(preliminary separation
of phases)
Mineralogical Analysis
