Physical and Chemical Methods in Soil Analysis

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Copyright © 2005 New Age International (P) Ltd., Publishers

Published by New Age International (P) Ltd., Publishers

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ISBN : 978-81-224-2411-9

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Agriculture is the mainstay of the economy of our country and only the sustainable

agriculture is likely to provide long term food production, development and poverty alleviation.

Modern civilization is facing a real threat from the rapid population outburst. Simultaneously

the per capita land area or land: man ratio is decreasing dangerously which is one of the main

reason for food insecurity in the near future. Since soil is the backbone of civilization and is the

most precious and vital natural resource, it must be thoroughly understood and conserved/

managed well for sustained agricultural production.

The present text book is a comprehensive analytical manual covering the aspects of soil

analysis in the major areas of Soil Physics and Soil Chemistry. Furthermore, the concept of soil

microbial biomass carbon and nitrogen is also dealt in detail. An important feature of this text

is that it describes not only the analytical procedures in detail but also furnishes sufficient

theoretical background on the subject matter. The fundamental principles of the analytical

methods have been discussed precisely and the theories explained well with mathematical

analysis and chemical reactions whenever required.

I hope that this text book would be very much useful for the undergraduate and post

graduate students of Agricultural Universities/Institutes in India, researchers, teachers and

those interested in the analytical study of the soil.

Finally I appreciate the authors’ untiring effort in giving shape to this present text.

I wish them all success in their endeavour.

Former Professor & Head —S.K. Gupta

Division of Agricultural Chemistry and

Soil Science, University of Calcutta

35, Ballygunge Circular Road

Kolkata–700 019

Former President, Agricultural Sciences Section

Indian Science Congress Association, 2000

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This text is primarily meant to cater the need of undergraduate and postgraduate students

of Agricultural Universities/Institutes in India and is expected to be of help to teachers and

researchers as well. An endeavour has been made to provide sufficient theoretical background

on the subject matter to ensure that the procedures are not followed merely to obtain a numerical

answer.

The text comprises of 4 major areas viz. Soil Physics, Soil Chemistry, Fundamental

Concepts of Instrumental Techniques and Fundamental Concepts of Analytical Chemistry. Each

topic is presented in a lucid and concise manner furnishing details of reagent preparation and

stepwise procedure, outlining precautions and additional notes wherever necessary. The

principles have been discussed briefly and theories explained well with mathematical derivations

and chemical equations as and when required. The analytical methods described in this text

are either being widely used or have been accepted throughout as standard. Various methods

have been explained in a simple and easily understandable language comprising of principle

with equipments and apparatus, procedure, observations and calculations.

Inspite of best efforts by the authors, the text may still have some discrepancies.

Suggestions for improvement from the readers will be highly appreciated.

—Dipak Sarkar

National Bureau of Soil Survey —Abhijit Haldar

and Land Use Planning (ICAR)

Sector-II, Block-DK, Salt Lake

Kolkata - 700 091

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The authors express their deep sense of gratitude to the following persons for their en￾couragement, help, co-operation and assistance in various capacities at different stages during

bringing out this document.

• Dr. K.S. Gajbhiye, Director, National Bureau of Soil Survey and Land Use Planning

(Indian Council of Agricultural Research), Nagpur for encouragement and support.

• Dr. Utpal Baruah, Principal Scientist, National Bureau of Soil Survey and Land Use

Planning (Indian Council of Agricultural Research), NER Centre, Jorhat for constant

support.

• Professor Shyamal Kumar Gupta (Retd.), University of Calcutta and Professor Saroj

Kumar Sanyal, Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West

Bengal for their inspiration and support.

• The Scientists of Regional Centre, National Bureau of Soil Survey and Land Use

Planning (Indian Council of Agricultural Research), Regional Centre, Kolkata spe￾cially Dr. D.S. Singh, Dr. A.K. Sahoo, Dr. K.D. Sah, Dr. K. Das, Dr. T.H. Das, Dr. D.C.

Nayak, Dr. D. Dutta, Dr. S.K. Gangopadhyay, Shri S. Mukhopadhyay, Smt. T.

Banerjee, Dr. T. Chattopadhyay for their constant support and encouragement with

valuable suggestions time to time.

• Shri B.K. Saha, Smt. Nirmala Kumar, Shri B.C. Naskar, Shri Pranabesh Mondal,

Shri Sourav Ghosh (Ex-SRF) and all others of National Bureau of Soil Survey and

Land Use Planning (Indian Council of Agricultural Research), Regional Centre, Kolkata

who rendered support and discharged their duties to accomplish the job.

• To all others who rendered their support to give the final shape to the document.

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Chapter Page

Forward (v)

Preface (vii)

Acknowledgements (ix)

1. INSTRUMENTAL TECHNIQUES : FUNDAMENTAL CONCEPTS ....................... 1

1.1 pH–General Discussion.......................................................................................... 1

1.1.1 Measurement of pH ........................................................................................ 4

1.1.2 Glass Electrode ............................................................................................... 4

1.1.3 Calomel Electrode ........................................................................................... 5

1.1.4 Electrode Potential Determination : Illustration with Calomel Electrode ;

Hydrogen Electrode and Standard Oxidation Potential .............................. 5

1.1.5 Potentiometric Method ................................................................................... 7

1.1.6 Liquid Junction Potential............................................................................... 8

1.1.7 Drifting of Soil pH .......................................................................................... 8

1.1.8 Experimental Determination of Cell e.m.f. ................................................... 9

1.1.9 Care and Maintenance ................................................................................... 9

1.2 Electrical Conductance–General Discussion ................................................. 10

1.2.1 Ohm’s Law (Resistance, Specific Resistance,.............................................. 10

Conductance, Equivalent Conductance)

1.2.2 Measurement of Conductivity...................................................................... 11

1.2.3 Wheatstone Bridge Principle ....................................................................... 12

1.2.4 Types of Conductivity Meters ...................................................................... 14

1.2.5 Care and Maintenance ................................................................................. 15

1.3 Colorimetry and Spectrophotometry–General Discussion

and Theoretical Consideration.......................................................................... 15

1.3.1 Beer–Lambert Law ....................................................................................... 16

1.3.2 Deviation from Beer’s Law ........................................................................... 17

1.3.3 Spectrophotometer : Instrumentation......................................................... 18

1.3.4 Standard Curve............................................................................................. 20

1.4 Flame Spectrometry–General Discussion and Elementary Theory ......... 20

1.4.1 Electromagnetic Radiation........................................................................... 20

  

1.4.2 Electromagnetic Spectrum........................................................................... 21

1.4.3 Wave Nature of Light ................................................................................... 21

1.4.4 Elementary Quantum Theory of Max Planck............................................. 23

1.4.5 Postulate’s of Bohr’s Theory......................................................................... 23

1.4.6 General Feature’s of Spectroscopy .............................................................. 24

1.4.7 General Discussion and Elementary Theory of .......................................... 25

Flame Spectrometry (Atomic Absorption Spectrometry

and Flame Photometry)

1.4.8 Flame Photometry ........................................................................................ 26

1.4.9 Care and Maintenance ................................................................................. 28

1.4.10 Atomic Absorption Spectrophotometer ....................................................... 29

(Instrumentation and Experimental)

1.4.11 Interferences ................................................................................................. 30

1.4.12 Safety Practices............................................................................................. 32

2. SOIL PHYSICS ................................................................................................................ 34

2.1 Particle Size Distribution ......................................................................................... 34

2.1.1 International Pipette Method ...................................................................... 36

2.1.2 Hydrometer Method ..................................................................................... 41

2.2 Aggregate Size Analysis by Wet Sieving Method ................................................... 44

2.3 Particle Density ........................................................................................................ 47

2.4 Bulk Density ............................................................................................................. 48

2.4.1 Core Sampler Method ................................................................................... 48

2.4.2 Clod Saturation Method ............................................................................... 49

2.5 Total Porosity ............................................................................................................ 50

2.6 Air Filled Porosity..................................................................................................... 51

2.6.1 Difference Method ........................................................................................ 51

2.6.2 Air Pycnometer Method ............................................................................... 52

2.6.3 Inter-relations ............................................................................................... 53

2.7 Total Surface Area Determination of Soil by Ethylene.......................................... 53

Glycol Equilibrium Method

2.8 Determination of Height of Capillary Rise of Water in Soil .................................. 55

2.9 Determination of ‘Single Value Physical Constants’ ............................................. 57

of Soil by Keen Racz Kowski Box Measurement

2.10 Soil Water Content ................................................................................................... 59

2.10.1 Soil Moisture Percent (Direct Method) ....................................................... 59

2.10.2 Neutron Probe Method (Indirect Method) .................................................. 60

2.11 Determination of Saturated Hydraulic Conductivity in Laboratory..................... 62

2.11.1 Constant Head Permeameter Method......................................................... 62

(For Very Porous Soils)

2.11.2 Falling Head Method (For Slowly Permeable Soils) .................................. 64

( xii )

2.12 Determination of Saturated Hydraulic Conductivity in Field............................... 65

2.12.1 Piezometer Method (Below Water Table) ................................................... 65

2.12.2 Inverted Auger Hole Method (Above Water Table).................................... 67

2.13 Infiltration ................................................................................................................. 67

2.14 Soil Moisture Constants ........................................................................................... 68

2.14.1 Hygroscopic Coefficient ................................................................................ 68

2.14.2 Moisture Equivalent ..................................................................................... 69

2.14.3 Field Capacity ............................................................................................... 70

2.14.4 Permanent Wilting Point ............................................................................. 71

2.14.5 Moisture Retention Curve ............................................................................ 73

2.14.6 Available Water ............................................................................................ 74

2.15 Oxygen Diffusion Rate (ODR).................................................................................. 74

2.16 Determination of Specific Heat of Soil .................................................................... 76

3. SOIL CHEMISTRY ......................................................................................................... 78

3.1 Electrometric Measurement of Soil pH ................................................................... 78

3.2 Determination of Buffering Capacity of Soil .......................................................... 80

3.3 Soil Acidity ................................................................................................................ 82

3.3.1 Total Acidity .................................................................................................. 82

3.3.2 Exchange Acidity .......................................................................................... 83

3.3.3 Extractable Acidity ....................................................................................... 84

3.3.4 Total Potential Soil Acidity .......................................................................... 86

3.3.5 pH-dependent Soil Acidity ........................................................................... 87

3.4 Electrical Conductivity ............................................................................................. 87

3.5 Organic Carbon ......................................................................................................... 89

3.6 Soil Microbial Biomass Carbon ................................................................................ 92

3.7 Total Nitrogen ........................................................................................................... 95

3.8 Mineralisable Nitrogen ............................................................................................ 98

3.9 Determination of Soil Microbial Biomass Nitrogen ............................................. 100

3.10 Total Phosphorus .................................................................................................... 100

3.11 Extractable Phosphorus Determination–General Discussion ............................. 101

3.11.1 Ammonium Fluoride–Hydrochloric Acid Extractable .............................. 103

Phosphorous of soils (Bray’s no. 1 Method)

3.11.2 Alkaline Extraction of Soil Phosphorous................................................... 104

(Olsen’s method)

3.12 Total Potassium ...................................................................................................... 109

3.13 Ammonium Acetate Extractable Potassium ......................................................... 110

3.14 Cation Exchange Capacity ..................................................................................... 112

3.14.1 Cation Exchange Capacity of Soils containing Calcium Carbonate.........115

3.15 Anion Exchange Capacity ...................................................................................... 116

3.16 Exchangeable Bases ............................................................................................... 118

3.16.1 Exchangeable Sodium ................................................................................ 118

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3.16.2 Exchangeable Calcium and Magnesium ................................................... 119

3.17 Exchangeable Calcium and Magnesium in Calcareous Soils .............................. 123

3.18 Micronutrients (DTPA Extractable Fe2+, Cu2+, Zn2+ and Mn2+) ............................ 125

3.19 Arsenic Determination by Conversion to their Hydrides and Aspiration into

AAS .......................................................................................................................... 125

3.20 Fluoride Estimation in Soil and Water ; SPADNS Method ................................. 128

3.21 Determination of Lime Requirement of Soil ......................................................... 130

3.22 Determination of Gypsum Requirement of Soil ................................................... 131

3.23 Determination of Lime Potential ........................................................................... 133

3.24 Available Sulphur Determination in Soil.............................................................. 134

3.25 Determination of Carbonate and Bicarbonate in Soil .......................................... 135

3.26 Determination of Chloride in Soil Extract ............................................................ 137

4. FUNDAMENTAL CONCEPTS OF ANALYTICAL CHEMISTRY ........................ 139

4.1 Equilibrium : Law of Mass Action ......................................................................... 139

4.2 Activity and Activity Coefficients .......................................................................... 140

4.3 Acid-Base Equilibria in Water : Ostwalds Dilution Law ..................................... 141

4.4 Solubility Product ................................................................................................... 141

4.5 Stability of Complexes ............................................................................................ 142

4.6 Titrimetry ................................................................................................................ 142

4.6.1 Titration ...................................................................................................... 142

4.6.2 Types of Reaction in Titrimetry ................................................................. 143

4.6.3 Strength....................................................................................................... 143

4.6.4 Percentage Strength ................................................................................... 143

4.6.5 Standard Solution ....................................................................................... 144

4.6.6 Normal Solution.......................................................................................... 144

4.6.7 Molar Slution .............................................................................................. 144

4.6.8 Molal Solution ............................................................................................. 144

4.6.9 Formal Solution .......................................................................................... 145

4.6.10 Factor of Solution........................................................................................ 145

4.6.11 Parts Per Million......................................................................................... 145

4.6.12 Percentage Composition by Weight........................................................... 145

4.6.13 Percentage Composition by Volume .......................................................... 145

4.6.14 Theory of Acid-Base Titrations .................................................................. 145

4.6.15 Principle of Acidimetry and Alkalimetry .................................................. 147

4.6.16 Indicators .................................................................................................... 147

4.6.17 Choice of Indicators .................................................................................... 148

4.7 Oxidation and Reduction Reactions : Electronic Interpretations ........................ 148

4.7.1 Redox Potential ........................................................................................... 150

4.7.2 Redox Indicators ......................................................................................... 152

4.7.3 Formal Potential ......................................................................................... 153

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