Chapter 9
Soil acid-base and redox reaction
Chapter 9 Soil acid-base and redox reaction
Section 1 The formation of soil acid-base
The acid-base reaction of soil
The acid-base reaction of soil is change in soil pH,Soil
pH is probably the single most important chemical
charecteristic of a soil,The knowledge of pH is needed to
understand important chemical processes such as ion
mobility,precipitation and dissolution equilibria,and
oxidation-reduction equilibria,A knowledge of pH is also
needed to understand nutrient availability to plants and the
negative response of many plant species to soil acidity.
The soil pH value in China is about 4.5-8.5.
一,Soil acidity
（ 一 ） The cause of soil acidity
1,Climatic factor
2,Biological factor
3,Fertilizer application and irrigation
1.The source of hydrogen ions
（ 1） Water dissociation
（ 2） Carbon dioxide
（ 3） Organic acid
（ 4） Inorganic acid (inorganic fertilizer)
（ 5） Acid rain
Acid rain
? Acid rain is caused by the
burning of fossil fuels,
? Burning oil,gas and coal in
power stations releases
Sulfuric Dioxide (SO2) into
the atmosphere,
? Burning oil and gasoline in
motor vehicles puts nitrogen
oxides (NOX) into the
atmosphere.
? These gases mix with water
droplets in the atmosphere
creating weak solutions of
nitric and sulfuric acids,
? When precipitation occurs
these solutions fall as acid
rain,
Exchangeable Hydrogen is the main
source of H+ at pH 6 and above,
Below pH 6 Aluminum is the main
source of H+ due to dissociation of Al
from clay minerals,Aluminum
becomes more soluble at lower pH’s
Al3+ + H20 ----> Al(OH)++ + H+
Al(OH)++ + H2O ---> Al(OH)2+ + H+
Al(OH)2+ + H20 ---> Al(OH)3 + H+
2,Aluminum activation in soil
（ 二 ） The types of soil acidity
1,Active acidity
Active Acidity –The activity of hydrogen ion in
the aqueous phase of a soil expressed as a pH value.
2,Soil potential acidity
(1) Strong acidity in soil
Colloid-Al3+ = Colloid + Al3+
Al3+ + 3H2O Al（ OH)3 + 3H+
(2) Acidity and weak acidity in soil
Al（ OH） 2+ + HOH Al（ OH） 2+ + H+
Al（ OH） 2+ + HOH Al（ OH） 3+ + H+
Or,Colloid-H+ H+
3,Soil exchangeable acidity
? Exchangeable acidity- The aluminum and
hydrogen that can be replaced from an acid
soil by an unbuffered salt solution such as
KCl or NaCl,(cmol（＋） /kg）
4,Soil hydrolytic acidity
CH3COONa + H2O CH3COOH + NaOH
H-Colloid Al + 4CH3COONa Na-Colloid 3Na
+ Al（ OH） 3 +4CH3COOH
Oxide -OH + CH3COONa Oxide-O-Na++ CH3COOH
二, Soil alkalinity
（ 一 ） The cause of soil alkalinity
1,Calcium carbonate hydrolysis
CaCO3 + H2O Ca2+ + HCO3- + OH-
CO2 + H2O HCO3- + H+
2,Sodium carbonate hydrolysis
(1)2NaHCO3 Na2CO3+H2O + CO2
(2)Na2SiO3 + H2CO3 Na2CO3 +SiO2+H2O
(3)CaCO3 +NaCl CaCl2 + Na2CO3
CaCO3 + Na2SO4 CaSO4+ Na2CO3
3,Exchangeable Sodium hydrolysis
Ca2+ 2Na+
Mg2+ + 4Na+ 2Na+ + Ca2+ + Mg2+Colloid Colloid
xNa + yH2O +CO2 （ x-y） Na+ + yNaOH
yH+Colloid
Colloid
（二） Affect the factors of soil alklization：
1,Climatic factor
2,Biological factor
3,Parent factor
Section 2 Index of soil acidity
Soil acidity is brief name of soil acid and base!
一,Intensity index of soil acidity
（一） pH value
pH - the negative log of the hydrogen ion(H+)
concentration in the soil water solution,
pH = - log [ H+]
（二） Lime potential
Lime potential will be introduced later course
(Agricultural Chemistry)
二,Index of soil alkalinty
（一） Total alkalinty
Total alkalinty including carbonate and bicarbonate in
soil solution or irrigation water.
Total alkalinty = CO32- + HCO3- (cmol(+)/L)
Lime reaction and lime soil:
（二） Exchangeable sodium percentage (ESP）
ESP is the percentage of exchangeable sodium ions to the total
soil exchangeable cations of all types in the soil sample,
Alkalinization-If a high proportion of exchange sites is occupied
by sodium ions,soils can become very basic with pH values of 8.5
to 10.5,These soils can become impermeable to water because
small soil particles that are dispersed by the sodium are entrapped
in the pores and seal them,These impermeable soils keep a water
layer on the surface,which cannot infiltrate,and these areas appear
“wet” longer than other adjacent soils.
Classification of solonetz in China,Light alkali-affected soil,ESP,
5－ 10％ ; Middle alkali-affected soil,ESP, 10－ 15％ ; Strong
alkali-affected soil,ESP, 15－ 20％ Alkali soil,ESP>30%.
ESP = [(exchangeable sodium ions )/(soil cations exchangeable capacity)]× 100
三, Affect the factors of soil acidity
1,Base saturation
2,CO2 differential pressure in the soil air
3,Soil moisture content
4,Condition of soil redox
Acid soil (Yunnan
Province,People's
Republic of China).
Section 3
Soil redox reaction
一,Soil redox system
Characteristics of Soil redox system:
① Soil redox system can be divided two system,inorganic
and organic systems.
② The organisms participates in soil redox reaction.
③ The soil is a heterogenesis system,Soil redox potential
is different in the field.
④ Equilibrium of soil redox is usually change.
1,Soil redox potential (Eh)
Eh- The potential that is generated between or
oxidation or reduction half-reaction and the standard
hydrogen electrode.
Oxidation ＋ ne ==== Reduction
二,Index of soil redox
][
][l o g059.0
][
][l o g 00
还原态
氧化态
还原态
氧化态
n
E
nF
RTEEh ????
2,The negative logarithm of the apparent electron
activity（ pe）
pe can be calculated by including the apparent activity of
electrons in equilibrium calculations of redox half-cell
reactions,In practice it is used as an alternative to Eh and at
25° C can be calculated from Eh values expressed in volts by
dividing by 0.059.
3,Relation between Eh and pH
Where m is number of protons in reaction.
1,Activity of microorganism
2,Content of labile organic matters
3,Content of easy oxidation-reduction inorganic
matters in soil
4,Metabolism of plant roots
5,Soil pH value
三,Affect the factors of redox
Section 4 Soil buffering
一, Concept of soil buffering
Soil buffering is the ability of soil to resist
change in pH.
二,Acid or alkali buffering of soil
（一） The principle of acid or alkali buffering of soil
HAc H+ + Ac-
NaAc + HCl HAc + NaCl
?-M + HCl -H + MCl ColloidColloid
][
][l o g
酸
盐??
apKpH
（ 二 ） Acid or alkali buffering system of soil
1,Carbonate system
pH P C O? ?6 03 23 2,l o g
CaCO3 + H2O +CO2 Ca2+ + 2HCO3-
2,Silicate system
?Mg2SiO4 + 4H+ Mg2+ + Si(OH)4
3,Exchangeable ions system
Ultimate pH-当土壤胶体上吸附的阳离子全部是致酸离子
（ H+和 Al3+）时，称为“盐基完全不饱和状态”，此时土
壤的 pH值称为“极限 pH值”,
4,Aluminum system
When pH<4.0,Al ions exist in Al(H2O)63+ form
2 2 42 3 3 2 2 2 8 4 2Al OH OH Al OH H O H O( ) ( ) ( )? ? ?? ?
OHOHOHAlOHOHAl 2612264362 12])()([6)(4 ?? ??
When pH>5.0,Al ions become Al(OH)3
precipitation,it will lose it’s buffering capacity.
5,Organic acid system
（三） The acid and alkali buffer capacity and
titration curve of soil (Studied by yourself!!)
(四 ) Affect the factors of acid or alkali buffering of soil
1,Soil inorganic colloid
2,Soil texture
3,Soil organic matters
三,The redox buffering of soil
(Studied by yourself!!)
Section 5 Soil acid-alkali and
redox with bioenvironment
一,The adaptability of organisms to
soil acid-alkali and redox
（一） The plants are suited to acid-alkali
Soil Acidity
in Australia
（二） Soil Eh Scope and plants growth
（三） Soil pH and Eh with soil microbial activity
二,Soil acid-alkali and redox with nutrient
organisms effectively
（一 ) Influence of soil acid-alkali to nutrient effectively
（二） Influence of soil redox to nutrient effectively
三,Soil acid-alkali and redox with
accumulation of toxicity matters
（一） Aluminum and manganese force and poison in
strong acid soil
pH<5.5，游离的铝离子达 0.2C mol/kg土时,就可使农作物
受 害。
幼苗期对铝极为敏感。
铝害表现：根系变粗短，影响养分吸收。
措施：施用石灰。
当交换锰（ Mn2+）达到 2-9Cmol/kg土,或植株干物质含锰量
超过 1000mg/kg时产生锰害。
豆类植物易产生锰害，禾本科植物抗性较强
措施：施用石灰,Ph>6.0;水稻土排水解除锰的毒害 。
（二） Soil redox with accumulation of
toxicity matters
Eh<200mv时,土壤中的铁锰化合物就从氧化态转化为还原态,
当 Eh<-100mv时,则低价铁 (Fe2+)浓度已超过高价铁 (Fe3+),会使
植物产生铁的毒害。
Eh<-200mv,就可能产生 H2S和丁酸等的过量积累,对水稻的含
铁氧化还原酶的活动有抑制作用,影响其呼吸、减弱根系吸收
养分的能力。在 H2S浓度高时,抑制植物根对磷、钾的吸收，
甚至出现磷、钾从根内渗出。
水田土壤大量施用绿肥等有机肥时常常发生 FeS的过
量积累,使稻根发黑,土壤发臭变黑,影响其地上部分
的生长发育。
四,Adjustment of Soil acid-alkali and redox
（一） Adjustment of soil acidity
The soil acidity can be adjusted by lime,The lime can
be divided by three main categories,which are
Calcium oxide (CaO),Calcium hydroxide [Ca(OH)2]
and Calcium carbonate(CaCO3).
Lime requirment = Soil volume × bulk density × CEC (1- base
saturation)
Lime requirment
Affect the factors of lime applied：
（ 1） Soil potential acidity and pH value,content of organic
matter,base saturation and soil texture etc.
（ 2） Adaptability of the plant to acid-alkali
（ 3） Lime types and applying methods
假设某红壤的 pH为 5.0,耕层土壤为 2250000公斤 /公顷，土壤含水量为 20％，阳离
子交换量为 10Cmol/kg土,盐基饱和度为 60%,试计算达到 pH=7时,中和活性酸和潜性酸
的石灰需要量 (理论值 )。
中和活性酸 pH=5时,土壤溶液中 [H+]=10-5,mol/kg土,则每公顷耕
层土壤含 H+离子为,
2250000× 20%× 10-5=4.5molH+/公顷
同理,pH=7时,每公顷土壤中含 H+离子为
2250000× 20%× 10-7=0.045mol H+/公顷
所以需要中和活性酸量为 4.5-0.045=4.455mol H+/公顷
若以 CaO中和,其需要量 4.455× (56/2) = 124.74 克
中和潜性酸,
2250000× (10 /100)× (1- 60/100)=90000 mol H+/公顷
90000× 56/2=2520000克 =2520公斤 /公顷
案例 1
（二） Adjustment of soil redox
Drainage ——— >Aeration——— >Oxidation
Irrigation——— >Anaeration——— >Reduction
Soil acid-base and redox reaction
Chapter 9 Soil acid-base and redox reaction
Section 1 The formation of soil acid-base
The acid-base reaction of soil
The acid-base reaction of soil is change in soil pH,Soil
pH is probably the single most important chemical
charecteristic of a soil,The knowledge of pH is needed to
understand important chemical processes such as ion
mobility,precipitation and dissolution equilibria,and
oxidation-reduction equilibria,A knowledge of pH is also
needed to understand nutrient availability to plants and the
negative response of many plant species to soil acidity.
The soil pH value in China is about 4.5-8.5.
一,Soil acidity
（ 一 ） The cause of soil acidity
1,Climatic factor
2,Biological factor
3,Fertilizer application and irrigation
1.The source of hydrogen ions
（ 1） Water dissociation
（ 2） Carbon dioxide
（ 3） Organic acid
（ 4） Inorganic acid (inorganic fertilizer)
（ 5） Acid rain
Acid rain
? Acid rain is caused by the
burning of fossil fuels,
? Burning oil,gas and coal in
power stations releases
Sulfuric Dioxide (SO2) into
the atmosphere,
? Burning oil and gasoline in
motor vehicles puts nitrogen
oxides (NOX) into the
atmosphere.
? These gases mix with water
droplets in the atmosphere
creating weak solutions of
nitric and sulfuric acids,
? When precipitation occurs
these solutions fall as acid
rain,
Exchangeable Hydrogen is the main
source of H+ at pH 6 and above,
Below pH 6 Aluminum is the main
source of H+ due to dissociation of Al
from clay minerals,Aluminum
becomes more soluble at lower pH’s
Al3+ + H20 ----> Al(OH)++ + H+
Al(OH)++ + H2O ---> Al(OH)2+ + H+
Al(OH)2+ + H20 ---> Al(OH)3 + H+
2,Aluminum activation in soil
（ 二 ） The types of soil acidity
1,Active acidity
Active Acidity –The activity of hydrogen ion in
the aqueous phase of a soil expressed as a pH value.
2,Soil potential acidity
(1) Strong acidity in soil
Colloid-Al3+ = Colloid + Al3+
Al3+ + 3H2O Al（ OH)3 + 3H+
(2) Acidity and weak acidity in soil
Al（ OH） 2+ + HOH Al（ OH） 2+ + H+
Al（ OH） 2+ + HOH Al（ OH） 3+ + H+
Or,Colloid-H+ H+
3,Soil exchangeable acidity
? Exchangeable acidity- The aluminum and
hydrogen that can be replaced from an acid
soil by an unbuffered salt solution such as
KCl or NaCl,(cmol（＋） /kg）
4,Soil hydrolytic acidity
CH3COONa + H2O CH3COOH + NaOH
H-Colloid Al + 4CH3COONa Na-Colloid 3Na
+ Al（ OH） 3 +4CH3COOH
Oxide -OH + CH3COONa Oxide-O-Na++ CH3COOH
二, Soil alkalinity
（ 一 ） The cause of soil alkalinity
1,Calcium carbonate hydrolysis
CaCO3 + H2O Ca2+ + HCO3- + OH-
CO2 + H2O HCO3- + H+
2,Sodium carbonate hydrolysis
(1)2NaHCO3 Na2CO3+H2O + CO2
(2)Na2SiO3 + H2CO3 Na2CO3 +SiO2+H2O
(3)CaCO3 +NaCl CaCl2 + Na2CO3
CaCO3 + Na2SO4 CaSO4+ Na2CO3
3,Exchangeable Sodium hydrolysis
Ca2+ 2Na+
Mg2+ + 4Na+ 2Na+ + Ca2+ + Mg2+Colloid Colloid
xNa + yH2O +CO2 （ x-y） Na+ + yNaOH
yH+Colloid
Colloid
（二） Affect the factors of soil alklization：
1,Climatic factor
2,Biological factor
3,Parent factor
Section 2 Index of soil acidity
Soil acidity is brief name of soil acid and base!
一,Intensity index of soil acidity
（一） pH value
pH - the negative log of the hydrogen ion(H+)
concentration in the soil water solution,
pH = - log [ H+]
（二） Lime potential
Lime potential will be introduced later course
(Agricultural Chemistry)
二,Index of soil alkalinty
（一） Total alkalinty
Total alkalinty including carbonate and bicarbonate in
soil solution or irrigation water.
Total alkalinty = CO32- + HCO3- (cmol(+)/L)
Lime reaction and lime soil:
（二） Exchangeable sodium percentage (ESP）
ESP is the percentage of exchangeable sodium ions to the total
soil exchangeable cations of all types in the soil sample,
Alkalinization-If a high proportion of exchange sites is occupied
by sodium ions,soils can become very basic with pH values of 8.5
to 10.5,These soils can become impermeable to water because
small soil particles that are dispersed by the sodium are entrapped
in the pores and seal them,These impermeable soils keep a water
layer on the surface,which cannot infiltrate,and these areas appear
“wet” longer than other adjacent soils.
Classification of solonetz in China,Light alkali-affected soil,ESP,
5－ 10％ ; Middle alkali-affected soil,ESP, 10－ 15％ ; Strong
alkali-affected soil,ESP, 15－ 20％ Alkali soil,ESP>30%.
ESP = [(exchangeable sodium ions )/(soil cations exchangeable capacity)]× 100
三, Affect the factors of soil acidity
1,Base saturation
2,CO2 differential pressure in the soil air
3,Soil moisture content
4,Condition of soil redox
Acid soil (Yunnan
Province,People's
Republic of China).
Section 3
Soil redox reaction
一,Soil redox system
Characteristics of Soil redox system:
① Soil redox system can be divided two system,inorganic
and organic systems.
② The organisms participates in soil redox reaction.
③ The soil is a heterogenesis system,Soil redox potential
is different in the field.
④ Equilibrium of soil redox is usually change.
1,Soil redox potential (Eh)
Eh- The potential that is generated between or
oxidation or reduction half-reaction and the standard
hydrogen electrode.
Oxidation ＋ ne ==== Reduction
二,Index of soil redox
][
][l o g059.0
][
][l o g 00
还原态
氧化态
还原态
氧化态
n
E
nF
RTEEh ????
2,The negative logarithm of the apparent electron
activity（ pe）
pe can be calculated by including the apparent activity of
electrons in equilibrium calculations of redox half-cell
reactions,In practice it is used as an alternative to Eh and at
25° C can be calculated from Eh values expressed in volts by
dividing by 0.059.
3,Relation between Eh and pH
Where m is number of protons in reaction.
1,Activity of microorganism
2,Content of labile organic matters
3,Content of easy oxidation-reduction inorganic
matters in soil
4,Metabolism of plant roots
5,Soil pH value
三,Affect the factors of redox
Section 4 Soil buffering
一, Concept of soil buffering
Soil buffering is the ability of soil to resist
change in pH.
二,Acid or alkali buffering of soil
（一） The principle of acid or alkali buffering of soil
HAc H+ + Ac-
NaAc + HCl HAc + NaCl
?-M + HCl -H + MCl ColloidColloid
][
][l o g
酸
盐??
apKpH
（ 二 ） Acid or alkali buffering system of soil
1,Carbonate system
pH P C O? ?6 03 23 2,l o g
CaCO3 + H2O +CO2 Ca2+ + 2HCO3-
2,Silicate system
?Mg2SiO4 + 4H+ Mg2+ + Si(OH)4
3,Exchangeable ions system
Ultimate pH-当土壤胶体上吸附的阳离子全部是致酸离子
（ H+和 Al3+）时，称为“盐基完全不饱和状态”，此时土
壤的 pH值称为“极限 pH值”,
4,Aluminum system
When pH<4.0,Al ions exist in Al(H2O)63+ form
2 2 42 3 3 2 2 2 8 4 2Al OH OH Al OH H O H O( ) ( ) ( )? ? ?? ?
OHOHOHAlOHOHAl 2612264362 12])()([6)(4 ?? ??
When pH>5.0,Al ions become Al(OH)3
precipitation,it will lose it’s buffering capacity.
5,Organic acid system
（三） The acid and alkali buffer capacity and
titration curve of soil (Studied by yourself!!)
(四 ) Affect the factors of acid or alkali buffering of soil
1,Soil inorganic colloid
2,Soil texture
3,Soil organic matters
三,The redox buffering of soil
(Studied by yourself!!)
Section 5 Soil acid-alkali and
redox with bioenvironment
一,The adaptability of organisms to
soil acid-alkali and redox
（一） The plants are suited to acid-alkali
Soil Acidity
in Australia
（二） Soil Eh Scope and plants growth
（三） Soil pH and Eh with soil microbial activity
二,Soil acid-alkali and redox with nutrient
organisms effectively
（一 ) Influence of soil acid-alkali to nutrient effectively
（二） Influence of soil redox to nutrient effectively
三,Soil acid-alkali and redox with
accumulation of toxicity matters
（一） Aluminum and manganese force and poison in
strong acid soil
pH<5.5，游离的铝离子达 0.2C mol/kg土时,就可使农作物
受 害。
幼苗期对铝极为敏感。
铝害表现：根系变粗短，影响养分吸收。
措施：施用石灰。
当交换锰（ Mn2+）达到 2-9Cmol/kg土,或植株干物质含锰量
超过 1000mg/kg时产生锰害。
豆类植物易产生锰害，禾本科植物抗性较强
措施：施用石灰,Ph>6.0;水稻土排水解除锰的毒害 。
（二） Soil redox with accumulation of
toxicity matters
Eh<200mv时,土壤中的铁锰化合物就从氧化态转化为还原态,
当 Eh<-100mv时,则低价铁 (Fe2+)浓度已超过高价铁 (Fe3+),会使
植物产生铁的毒害。
Eh<-200mv,就可能产生 H2S和丁酸等的过量积累,对水稻的含
铁氧化还原酶的活动有抑制作用,影响其呼吸、减弱根系吸收
养分的能力。在 H2S浓度高时,抑制植物根对磷、钾的吸收，
甚至出现磷、钾从根内渗出。
水田土壤大量施用绿肥等有机肥时常常发生 FeS的过
量积累,使稻根发黑,土壤发臭变黑,影响其地上部分
的生长发育。
四,Adjustment of Soil acid-alkali and redox
（一） Adjustment of soil acidity
The soil acidity can be adjusted by lime,The lime can
be divided by three main categories,which are
Calcium oxide (CaO),Calcium hydroxide [Ca(OH)2]
and Calcium carbonate(CaCO3).
Lime requirment = Soil volume × bulk density × CEC (1- base
saturation)
Lime requirment
Affect the factors of lime applied：
（ 1） Soil potential acidity and pH value,content of organic
matter,base saturation and soil texture etc.
（ 2） Adaptability of the plant to acid-alkali
（ 3） Lime types and applying methods
假设某红壤的 pH为 5.0,耕层土壤为 2250000公斤 /公顷，土壤含水量为 20％，阳离
子交换量为 10Cmol/kg土,盐基饱和度为 60%,试计算达到 pH=7时,中和活性酸和潜性酸
的石灰需要量 (理论值 )。
中和活性酸 pH=5时,土壤溶液中 [H+]=10-5,mol/kg土,则每公顷耕
层土壤含 H+离子为,
2250000× 20%× 10-5=4.5molH+/公顷
同理,pH=7时,每公顷土壤中含 H+离子为
2250000× 20%× 10-7=0.045mol H+/公顷
所以需要中和活性酸量为 4.5-0.045=4.455mol H+/公顷
若以 CaO中和,其需要量 4.455× (56/2) = 124.74 克
中和潜性酸,
2250000× (10 /100)× (1- 60/100)=90000 mol H+/公顷
90000× 56/2=2520000克 =2520公斤 /公顷
案例 1
（二） Adjustment of soil redox
Drainage ——— >Aeration——— >Oxidation
Irrigation——— >Anaeration——— >Reduction
