Soil Sampling, Preparation and Analysis Kim H. Tan The University of Georgia Athens, Georgia Marcel Dekker, Inc. New York* Basel Hong Kong
CONTENTS Preface iii Chapter 1 PRINCIPLES OF SOIL SAMPLING 1 1.1 General Principles 1 1.2 Soil Concept for Sampling 2 1.3 Types of Soil Sampling 5 1.3.1 Simple Random Sampling 6 1.3.2 Systematic Sampling 6 1.3.3 Stratified Sampling 7 1.3.4 Compositing 8 1.4 Mechanics of Sampling 9 1.4.1 Shallow Sampling 9 1.4.2 Deep Sampling 10 1.4.3 Soil Profile Sampling 10 1.4.4 Time of Sampling 11 1.5 Size and Accuracy of Sampling 12 vu
viii Chapter 2 SAMPLE PREPARATION 17 2.1 Sample Preservation 17 2.2 Sample Storage 20 2.3 Sample Preparation 21 2.4 Grinding and Sieving 21 2.4.1 Grinding 21 2.4.2 Sieving 22 2.4.3 Errors in Grinding and Sieving 23 2.5 Reduction in Sample Size 25 Chapter 3 ERRORS AND VARIABILITY OF SOIL ANALYSIS 27 3.1 Measure of Accuracy 27 3.2 Measure of Precision 28 3.3 Measure of Bias 30 3.4 Types of Errors 32 3.4.1 Determinate Errors 32 3.4.2 Indeterminate Errors 34 3.5 Rejection of Results 35 3.5.1 Checking for Accuracy 35 3.5.2 Checking for Precision 38 3.5.3 Checking for Bias 39 3.6 Statement of Results 40
ix Chapter 4 METHODS OF SOIL CHEMICAL ANALYSIS 42 4.1 Purpose and Use 42 4.2 Soil Testing 43 4.2.1 Monitoring 44 4.2.2 Determination of Nutrient Status 45 4.2.3 Plant Testing 45 4.2.4 Tissue Testing 47 4.3 Soil Analysis in Pedology and Soil Chemistry 48 4.3.1 Traditional Soil Analysis 48 4.3.2 Isolation and Analysis of Soil Constituents 49 4.3.3 Micropedological Analysis 49 4.3.4 Analysis of Soils in Situ 50 4.4 Types of Soil Chemical Analysis 51 4.4.1 Qualitative and Quantitative Analysis 51 Chapter 5 DETERMINATION OF SOIL WATER 56 5.1 Definitions and Principles 56 5.2 Determination of Total Soil Water Content 59 5.2.1 Direct Determination of Water Content 59 5.2.2 Indirect Determination of Water Content 61
5.3 Determination of Available Water Content 62 5.3.1 Pressure-Plate Method 62 5.3.2 Alternative Methods 65 5.4 Determination of Soil Moisture Tension 68 Chapter 6 DETERMINATION OF SOIL TEXTURE 73 6.1 Definition and Principles 73 6.2 Hydrometer Method 78 6.2.1 Dispersion Reagent 79 6.2.2 Procedure 79 6.3 Centrifuge Method 81 6.3.1 Reagents 81 6.3.2 Procedure 82 6.4 Pipette Method 84 6.4.1 Procedure. 84 Chapter 7 DETERMINATION OF SOIL DENSITY AND POROSITY 86 7.1 Definition and Principles 86 7.2 Measurement of Bulk Density 88 7.2.1 Bulk Density Measurement of Disturbed Soil 88
xi 7.2.2 Clod Method 90 7.3 Measurement of Particle Density 91 7.3.1 Method Using a Graduated Cylinder 91 7.3.2 Method Using a Volumetric Flask 93 7.4 Determination of Pore Spaces 94 Chapter 8 SOIL ph MEASUREMENT 96 8.1 Definition and Principles 96 8.2 Indicator or Colorimetric Method 99 8.3 Potentiometric Method 103 8.4 Factors Affecting ph Measurements 106 8.4.1 Suspension Effect 106 8.4.2 Dilution Effect 106 8.4.3 Sodium Effect 107 8.5 Water ph Versus Buffer ph 107 8.6 Determination of Lime Requirement 109 8.7 Determination of Lime Potential 112 Chapter 9 CATION EXCHANGE CAPACITY DETERMINATION 114 9.1 Definition and Principles 114 9.2 Factors Affecting CEC Determination 117 9.2.1 ph of the Leaching (Displacing) Solution 117 9.2.2 Nature of the Exchange Complex 118
xii 9.2.3 Nature and Concentration of the Leaching Solution 119 9.2.4 Presence of Undesirable Interactions 121 9.2.5 Analytical Approach 121 9.2.6 Limitations of the Analysis 122 9.3 Methods of CEC Determination 123 9.3.1 Ammonium Acetate (NH 4 OAc) Method 123 9.3.2 Alternative Method 126 9.3.3 Determination of ECEC 127 9.3.4 Determination of CEC p 128 9.3.5 Determination of CEC t 130 9.4 Methods for Determination of Exchangeable H + 132 9.4.1 Barium Chloride-TEA Method 132 9.4.2 Potassium Chloride (KCl) Method 133 Chapter 10 DETERMINATION OF MACROELEMENTS 135 10.1 Determination of Soil Nitrogen 135 10.1.1 Forms of Nitrogen in Soils 10.1.2 Determination of Total N 10.1.3 Kjeldahl Method 10.1.4 Determination of Exchangeable NH 4 + 10.1.5 Determination of NO 3 " 10.1.6 Determination of NO 2 ' 135 138 139 148 149 152
xiii 10.2 Determination of Soil Phosphorus 153 10.2.1 Forms of Phosphorus in Soils 153 10.2.2 Determination of Total P 159 10.2.3 Determination of Organic P 162 10.2.4 Determination of Available P 165 10.3 Determination of Potassium 170 10.3.1 Forms of Potassium in Soils 170 10.3.2 Determination of Total K 173 10.3.3 Determination of Available K 174 10.4 Determination of Sodium 175 10.4.1 Forms of Sodium in Soils 175 10.4.2 Determination of Total Na 177 10.4.3 Determination of Exchangeable Na 178 10.5 Determination of Calcium 178 10.5.1 Forms of Calcium in Soils 178 10.5.2 Determination of Total Ca 180 10.5.3 Determination of Exchangeable Ca 180 10.5.4 Determination of Dilute Acid Soluble Ca 180 10.6 Determination of Magnesium 181 10.6.1 Forms of Magnesium in Soils 181 10.6.2 Determination of Total Mg 182 10.6.3 Determination of Exchangeable Mg 182 10.6.4 Determination of Dilute Acid Soluble Mg 182
xiv 10.7 Determination of Sulphur 183 10.7.1 Forms of Sulphur in Soils 183 10.7.2 Determination of Total S 186 10.7.3 Determination of Inorganic S 187 Chapter 11 DETERMINATION OF MICROELEMENTS 189 11.1 Determination of Aluminum in Soils 189 11.1.1 Forms of Aluminum in Soils 189 11.1.2 Determination of Total Al 191 11.1.3 Determination of Exchangeable Al 193 11.2 Determination of Iron in Soils 194 11.2.1 Forms of Iron in Soils 194 11.2.2 Determination of Total Fe 196 11.2.3 Determination of Exchangeable Fe 196 11.2.4 Determination of Available Fe 197 11.2.5 Determination of Free and Amorphous Fe 198 11.3 Determination of Silicon in Soils 199 11.3.1 Forms of Silicon in Soils 199 11.3.2 Determination of Total Si 202 11.4 Determination of Manganese in Soils 204 11.4.1 Forms of Manganese in Soils 204 11.4.2 Determination of Total Mn 205 11.4.3 Determination of Exchangeable Mn 206 11.4.4 Determination of Available Mn 207
xv 11.5 Determination of Copper in Soils 207 11.5.1 Forms of Copper in Soils 207 11.5.2 Determination of Total Cu 209 11.5.3 Determination of Exchangeable Cu 210 11.5.4 Determination of Available Cu 211 11.6 Determination of Boron in Soils 211 11.6.1 Forms of Boron in Soils 211 11.6.2 Determination of Total B 213 11.6.3 Determination of Available B 215 11.7 Determination of Molybdenum in Soils 216 11.7.1 Forms of Molybdenum in Soils 216 11.7.2 Determination of Total Mo 218 11.7.3 Determination of Available Mo 218 11.8 Determination of Zinc in Soils 219 11.8.1 Forms of Zinc in Soils 219 11.8.2 Determination of Total Zn 220 11.8.3 Determination of Exchangeable Zn 221 11.8.4 Determination of Available Zn 222 Chapter 12 DETERMINATION OF SOIL ORGANIC MATTER 223 12.1 Definition and Principles 223 12.2 Determination of Total Organic C 226 12.2.1 Dry Combustion Method 226 12.2.2 Alternative Method 228
xvi 12.3 Determination of Oxidizable Organic C 229 12.3.1 Walkley-Black Wet Combustion Method 231 12.4 Determination of Humic Matter 232 12.4.1 Extraction of Soil Humic Matter 234 12.4.2 Extraction of Aquatic Humic Matter 236 12.4.3 Determination of Total Acidity of Humic Matter 238 12.4.4 Determination of Carboxyl and Phenolic-OH Groups 239 Chapter 13 SPECTROPHOTOMETRY AND COLORIMETRY 242 13.1 Definition and Principles 242 13.1.1 Absorption Spectrophotometry 243 13.1.2 Principles of Light Absorption 244 13.1.3 Law of Lambert and Bouger 245 13.1.4 Beer's Law 246 13.1.5 Law of Lambert and Beer 246 13.2 Visible Light and UV Spectrophotometers 247 13.2.1 Single Beam and Double Beam Spectrophotometers 249 13.2.2 Source of Visible Radiation 250 13.2.3 Source of Ultraviolet Radiation 250 13.2.4 Monochromators 251 13.2.5 Detectors 254
xvii Chapter 14 FLAME PHOTOMETRY 255 14.1 Definition and Principles 255 14.2 Atomic Absorption Spectroscopy 256 14.2.1 Principles of Atomic Absorption 257 14.2.2 Instrumentation 258 14.2.3 Samples and Sample Preparation 265 14.2.4 Interferences 266 14.3 Atomic Emission Spectroscopy 269 14.3.1 Principles of Atomic Emission 269 14.3.2 Emission Spectrographic Methods 271 14.3.3 Plasma Emission Spectroscopy 274 14.4 Detection Limits of Atomic Absorption and Plasma Emission Spectroscopy 276 Chapter 15 INFRARED SPECTROSCOPY 278 15.1 Definition and Principles 278 15.2 Origin of Spectra 280 15.3 Instrumentation and Sources of Infrared Radiation 284 15.3.1 Primary Source of Radiation 284 15.3.2 Detectors 284 15.4 Sample Preparation 285 15.4.1 Gas Samples 285 15.4.2 Liquid Samples 285 15.4.3 Solid Samples 285
xvm 15.5 Infrared Analysis of Humic Matter 286 15.5.1 Procedures 286 15.5.2 Infrared Spectra of Humic Matter 287 15.5.3 Methylation of Humic Acids 291 15.6 Infrared Analysis of Soil Clays 292 15.6.1 Materials and Pretreatments 292 15.6.2 Procedures 292 15.6.3 Infrared Spectra of Soil Clays 294 Chapter 16 X-RAY DIFFRACTION ANALYSIS 299 16.1 Definition and Principles 299 16.2 Instrumentation and Principles of X-ray Diffraction 303 16.2.1 Sources of X-ray Radiation 303 16.2.2 Principles of X-ray Diffraction 305 16.3 Qualitative X-ray Diffraction Spectrometry 308 16.3.1 Pretreatments 308 16.3.2 Mounting Techniques of Samples in XRD 311 16.3.3 Preparation of Oriented Glass Slide Samples 312 16.3.4 Preparation of Random Powder Samples 313 16.3.5 Diffractograms of Clay Minerals 313
xix 16.4 Quantitative X-ray Diffraction Spectrometry 327 16.4.1 Quantitative Interpretations of Diffractograms 328 Chapter 17 DIFFERENTIAL THERMAL ANALYSIS 329 17.1 Definition and Principles 329 17.2 Instrumentation 332 17.3 DTA of Soil Minerals and Organic Matter 335 17.3.1 Sample Preparation 335 17.3.2 Sample Size 345 17.3.3 Sample Packing 347 17.3.4 Furnace Atmosphere 348 17.3.5 Heating Rate 349 17.4 Qualitative Interpretation of DTA of Soil Minerals 350 17.5 Qualitative Interpretation of DTA of Organic Matter 357 17.6 Quantitative Interpretation of DTA of Soil Minerals 358 17.6.1 Preparation of a Standard Curve 360 Appendix A Fundamental Constants 363 Appendix B Greek Alphabet 364 Appendix C Atomic Weights of the Major Elements in Soils 365 Appendix D X-ray Diffraction 26 d-spacing Conversion Table 368
xx Appendix E U.S. Weights and Measures 369 Appendix F International System of Units (SI); 371 Factors for Converting U.S. Units into SI Units 371 References and Additional Readings 375 Index 392