Introduction to Soil Chemistry

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198 speciation to consider all possible species that might be present in the compartment. It is also important to consider the changes that a species is likely to undergo during the sampling and analytical procedures to which it will be subjected. This topic is discussed further in Section 10.5 [1,2]. 10.1. CATIONS Any positive chemical species can be considered a cation or as being in a cationic form. Some will be present as relatively simple, single-oxidation-state cations, while others may be more complex in that they may have several oxidation states and the cations may have oxygens or hydroxy groups associated with them. In all cases cations will associate with water molecules. Thus it is common to find them expressed as hydrated or hydroxide species. Such a representation more closely resembles the actual condition of cations in soil, particularly if the discussion relates to cations in the soil solution. This brings up a troublesome question or problem. When a cation is removed (extracted) from a solid matrix into an extracting solution, a species change most likely occurs. In the solid matrix the cation may not be associated with water molecules, while in solution it most certainly will be. For hydrated species the amount of associated water and the activity will also change. This raises the issue of the actual species present in the solid matrix. When analyzing for a specific cation species or discussing cation speciation in soil, it is important to keep this issue and problem in mind. Molybdenum should be discussed in this section because it is a metal; however, it is always present in soil as an oxyanion and so will be discussed in the next section [3,4]. 10.1.1. Simple Cations in Soil Simple cations are those that exist in only one oxidation state in soil and are associated with water, although they may also be chelated and form other associations with inorganic and organic components. The alkali and alkaline-earth metals are examples of relatively simple cations that occur in only one oxidation state and are surrounded by waters of hydration in the soil solution. The most common in soil, in order of decreasing abundance, are calcium (Ca 2+ ), magnesium (Mg 2+ ), potassium (K + ), and sodium (Na + ). Sodium is typically present in small amounts in high-rainfall areas, whereas it may be relatively high in low-rainfall areas. Although simple, these cations can occur as a number of different species. They will be present as exchangeable or in solution as hydrated cations. They can be part of the inorganic component structure, for example, as in isomorphous substitution, or be trapped between clay layers. They will also be associated with organic matter and with colloidal inorganic and organic matter,
cations 199 and chelated species. In many cases these cation species are further grouped into those available to plants and those that are unavailable. If a more detailed grouping is needed, species can be further divided into readily, slowly, very slowly, and nonavailable species. Another simple cation commonly occurring in soil is ammonium (NH4 + ). Because of the unique role and chemistry of nitrogen and nitrogen species in soil, it will be discussed separately in Section 10.3 [5,6]. 10.1.2. Complex Cations in Soil Complex cations are those that can occur in several oxidation states in soil and are often associated with oxygen and hydroxy groups while still carrying a positive charge. The periodic table contains more than 65 metals that may be present as complex cations. Of these, only a few are common in soil. Even those that are not common in soil will, if present, occur predominately in one oxidation state under normal soil conditions. No attempt will be made to cover all these cations; rather, a limited number of the more important will be presented to illustrate the chemistry of complex cations in soil. Examples of cations, which are present in significantly lower concentrations than the simple cations, are iron, manganese, zinc, copper, nickel, and cobalt. Except for cobalt, these have multiple oxidations states in soil as shown in Table 10.1. Because of their multiple oxidation states they may be present as Table 10.1. Common Important Ionic Species in Soil a Element/Compound Cations b Anions Nitrogen + NH4 NO3 - ,NO2 -c Phosphorus None H2PO4 - , HPO4 2- ,PO3 3- Potassium K + None Sulfur None S2- ,SO4 2- Chlorine None Cl-d Carbon None HCO3 - ,CO3 2- Iron Fe2+ , Fe(OH)2 + , Fe(OH) 2+ ,Fe3+ None Manganese Mn2+ ,Mn3+ Mn4+e None Copper Cu2+ , Cu(OH) + None Zinc Zn2+ , Zn(OH) + None Nickel Ni2+ ,Ni3+ None Boron None H2BO3 - Cobalt Co2+ None Molybdenum None 2- - MoO4 , HMO4 a Only elements and compounds commonly found in multiple oxidation states are listed. b In some cases species in this column may exist in soil under certain conditions; however, they are not common. c Nitrogen oxides and nitrogen gas from denitrification will also be present. d Any halide found in soil solution will be present as its anion. e Often found in mixed oxidation states.
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Introduction to Soil Chemistry Anal
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CHEMICAL ANALYSIS A SERIES OF MONOG
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Copyright © 2005 by John Wiley & S
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CONTENTS PREFACE xiii CHAPTER 1 SOI
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contents ix 4.14. Conclusion 89 Pro
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contents xi CHAPTER 10 SPECIATION 1
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xiv preface Moisture levels can cha
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CHAPTER 1 SOIL BASICS I MACROSCALE
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soil basics i 3 Mollisol Ap 0 - 17.
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soil basic i 5 Spodosol Oi 0 - 2.5
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horizonation 7 or basic.Thus, the t
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horizonation 9 Table 1.2. Major-Min
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peds 11 As would be expected, only
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peds 13 Figure 1.7. Peds isolated f
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P soil color 15 B P = pores B = bri
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soil naming 17 Under most condition
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soil chemistry, analysis, and instr
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ibliography 21 thus increased oxida
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CHAPTER 2 SOIL BASICS II MICROSCOPI
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O O Si O O d - d H H + d + O soil s
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d - Si O O O Al O O H d+ O O HO OH
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O HO O O O HO O O Si O Al O Si O O
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soil solids 31 the name taken from
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onding considerations 33 The two op
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surface features 35 Because differe
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energy considerations 37 side-by-si
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In Figure 2.5 the path to the right
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H O H H O C Na +- O O H H O H H O H
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eferences 43 2.7. Explain how the r
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CHAPTER 3 SOIL BASICS III THE BIOLO
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animals 47 C Figure 3.2. An ant col
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plants 49 Grasses and other similar
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plants 51 Rhizosphere Figure 3.4. I
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microorganisms 53 Table 3.1. Design
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microorganisms 55 microaerophilic,
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ioorganic 57 activity may be increa
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organic compounds 59 and may contai
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organic compounds 61 Table 3.3. Fun
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R 2C R organic compounds 63 O C - O
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analysis 65 3.7.1. Analysis for Ani
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problems 67 oxide by components in
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eferences 69 6. Bais HP, Park S-W,
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CHAPTER 4 SOIL BASICS IV THE SOIL A
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water 73 The soil atmosphere also c
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D C water 75 B Figure 4.3. A wide-d
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compounds in solution 77 tion is li
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+ NH4 + NH4 H H O + NH4 H H H + NH
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organic ions in solution 81 consequ
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distribution between soil solids an
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oxidative and reductive reactions i
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measuring soil water 87 soil is rep
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problems 89 blocks, and thermocoupl
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eferences 91 8. Bohn HL, McNeal BL,
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94 electrical measurements Figure 5
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96 electrical measurements 1200 100
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98 electrical measurements Referenc
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100 electrical measurements Standar
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102 Table 5.1. Ion-Selective Electr
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104 electrical measurements In addi
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106 electrical measurements along w
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108 electrical measurements cools w
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110 electrical measurements Science
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112 titrimetric measurement pH 13 1
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114 titrimetric measurement Table 6
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116 titrimetric measurement H 3 O +
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118 titrimetric measurement Because
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120 titrimetric measurement Soil Sa
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122 titrimetric measurement 6.6. NI
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124 titrimetric measurement - + X +
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126 titrimetric measurement REFEREN
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128 extraction Organic compounds, i
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130 extraction 3. What is the distr
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132 extraction All nonaqueous solve
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134 extraction Table 7.2. Character
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136 extraction Figure 7.3. Solution
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138 extraction Figure 7.5. A microw
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140 extraction serious interference
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142 extraction taining one to sever
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144 extraction Cohen DR, Shen XC, D
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146 extraction ultrasound; Applicat
Page 166 and 167: 148 spectroscopy although technical
Page 168 and 169: 150 spectroscopy Incident X-rays q
Page 170 and 171: 152 spectroscopy with cellulose or
Page 172 and 173: 154 spectroscopy extract components
Page 174 and 175: 156 spectroscopy 8.6. ULTRAVIOLET A
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Page 178 and 179: 160 spectroscopy to scratch them. W
Page 180 and 181: 162 spectroscopy Data Concentration
Page 182 and 183: 164 spectroscopy these make analysi
Page 184 and 185: 166 spectroscopy Table 8.1. Importa
Page 186 and 187: 168 spectroscopy nance (NMR) spectr
Page 188 and 189: 170 spectroscopy nitrogen containin
Page 190 and 191: 172 spectroscopy 7. Bernick MB, Get
Page 193 and 194: CHAPTER 9 CHROMATOGRAPHY Chromatogr
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Page 197 and 198: gas chromatography 179 Figure 9.3.
Page 199 and 200: gas chromatography 181 Table 9.3. C
Page 201 and 202: gas chromatography 183 Gas tight sy
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Page 205 and 206: thin-layer chromatography 187 They
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Page 209 and 210: conclusion 191 then a pure sample o
Page 211: eferences 193 U.S. Environmental Pr
Page 214 and 215: 196 speciation - Al H 2 O K H2O H2O
Page 218 and 219: 200 speciation many more species th
Page 220 and 221: 202 speciation atomic absorption is
Page 222 and 223: 204 speciation Table 10.2. Common O
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Page 230 and 231: 212 index Bioreactor, 124 Bioremedi
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Page 236 and 237: 218 index TMS, see Tetramethylsilan
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Page 240 and 241: Vol. 117 Applications of Fluorescen
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Introduction to Soil Chemistry

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