Chapter 4
Soil texture and structure
Section 1
Soil three phases Constitution
一,Soil density and bulk density
（ 一 ） Soil density ( or Particle density)
Soil density is the density of the solid soil particles only; the
measurement does not include water weight or pore (air) space,The
dominant soil minerals- quartz,feldspars,micas,and clay minerals-
average approximately 2.65 g/cm3,the,standard” value used in
calculations if particle density is not measured.
Individual minerals have densities from 2.0 g/cm3 for bauxite
(aluminum ore) to 5.3 for hematite (iron ore) or 7.6 for galena (lead
ore).
表 4 － 2 一种森林土壤表层各级土粒的密度粒级 （粒径毫米） 腐殖质 （克 / 千克 ) 密度 ( 克 / 厘米
3
)
全土样
0,1 0 ～ 0,0 5
0,0 5 ～ 0,0 1
0,0 1 ～ 0,0 0 5
0,0 0 5 ～ 0,0 0 1
< 0,0 0 1
2 9,5
0
4,3
1 4,8
5 3,7
6 4,2
2,6 2
2,6 6
2,6 6
2,6 2
2,5 9
2,5 9
表 4 - 1 土壤中常见组分的密度 ( 克 / 厘米
3
)
石 英正长石斜长石白云母黑云母角闪石辉 石纤铁矿
2,6 0 ～ 2,6 8
2,5 4 ～ 2,5 7
2,6 2 ～ 2,7 6
2,7 7 ～ 2,8 8
2,7 0 ～ 3,1 0
2,8 5 ～ 3,5 7
3,1 5 ～ 3,9 0
3,6 0 ～ 4,1 0
赤铁矿磁铁矿三水铝石高岭石蒙皂石伊利石腐殖质
4,9 0 ～ 5,3 0
5,0 3 ～ 5,1 8
2,3 0 ～ 2,4 0
2,6 1 ～ 2,6 8
2,5 3 ～ 2,7 4
2,6 0 ～ 2,9 0
1,4 0 ～ 1,8 0
（ 二 ） Soil bulk density
1,Bulk density,the density for a volume of soil as it exists
naturally,includes any air space and organic materials in the
soil volume.
ρb = (mass of dry soil)/(total volume of soil) = Ms/Vt
= Ms/(Vs + Vw +Va)
A recently cultivated topsoil is likely to have a bulk density
in the range from 0.9 to 1.2 g/cm3,while a compact subsoil may
have a bulk density of 1.6 g/cm3 or even more.
Uses of soil bulk density：
① To calculate soil porosity(p0):
② To calculate soil weight
③ To calculate storage of soil compositions
④ To calculate total water storage capacity
and irrigation (or drainage) quota.
2,Bulk density in water
= (soil mass over-dry)/(precipitation volume)
3,Affect the factors of soil bulk density:
Texture,structure,content of organic matter,and various
nature factors and anthropogenic factors.
P0 = 1- (Bulk density/soil density)
(一 ),Soil three phases constitution and porosity
二,Soil three phases constitution and pore
小孔隙大孔隙
1,Index three phases constitution
Solid phase (%) =（ solid volume /soil body volume) × 100
Liquid phase (%) =（ liquid volume /soil body volume) × 100
Gas phase (%) =（ air volume /soil body volume) × 100
2,Soil porosity:
Soil porosity is the percentage of the volume of pores to
the total volume of soil.
Soil porosity ＝ 1－ Solid phase (%)
= Liquid phase (%) + Gas phase (%)
The void ratio is the ratio of the volume of pores to the volume of
solids.
Void ratio = (volume of pores)/(volume of solids)
(二 ),Calculation of three phases constitution and porosity
1,Solid ratio
Solid ratio =（ bulk density /density） = ρb/ ρp
2,Liquid ratio (volumetric water content)
θm = (mass of water /mass of dry soil) = MW/MS
θv = (volume of water/ total volume of soil) = Vw/Vt
= Vw/(Vs+Vw+Va) = θm × ρb
3,Void ratio
3,Gas phase ratio
Porosity(P0) =1- solid phase ratio =1- bulk density /density）
= ρb/ ρp
Gas phase ratio = porosity- volumetric water content = P0- θv
4,Actual volume ratio
Solid phase ratio ＝ actual volume ratio－ volumetric water content
Gas phase ratio = 1－ actual volume ratio
Soil three phases ratio
＝ solid phase ratio,volumetric water content,gas phase ratio
(三 ),Suitable soil three phases ratio：
Solid phase ratio is about 50%，
volumetric water content is 25% to 30%，
Gas phase ratio is 15% to 25%.
(一 ) Types of soil particle：
Mineral soil particle and organic soil particle
Single particle and compound particle
Primary particle and second particle
(二 ) Soil particle fraction (soil separates)
Natural soils are comprised of soil particles of varying
sizes,The soil particle-size groups,called soil particle
fraction (soil separates),are sands (the coarsest),silts,
and clays (the smallest).
一,Soil particle and particle fraction (soil separates)
Section 2 Soil texture
Particle Diameter Size
Soil particle diameters
range over 4 orders of
magnitude
– Boulders
– Sand
– Silt
– Clay
Physical sandy particle,
1 mm to 0.01 mm.
Physical clay particle,
< 0.01 mm
Kachinsky classification system of soil separates
Soil particle
Classification system of soil separates,(mm)
Diameter International USDA Kachinsky Chinese
Boulders >2 >2 > 1 >1
Sand 2-0.02 2-0.05 1-0.05 1-0.05
Silt 0.02-0.002 0.05-0.002 0.05-0.001 0.05-0.002
Clay 〈 0.002 〈 0.002 〈 0.001 〈 0.002
(一 ） Soil mechanical composition
（ 二 ） Soil texture
1.Concept,Soil texture-The relative proportions of the
various soil separates in a soil.
2,Classification of soil texture
二,Soil mechanical composition and texture
(1) International classification：
The textural triangle is used to determine the soil textural
name after the percentages of sand (2-0.02mm),silt (0.02-0.002
mm),and clay (<0.002 mm) are determined from a laboratory
analysis.
The main criterion of classification：
Clay <15% is sand and loamy groups;
15％－ 25％ is clay loam group;
>25% is clay group.
When soil contains silt >45%,soil will be called,silty” ；
When soil contains sand in 55%-85%,called,sandy”,
When soil contains sand >85%,called,loamy sand”or,sand”.
The U.S,Dept,of Agri,(USDA)
Soil texture
表 4 － 6 卡钦斯基土壤质地基本分类 （简制）
质地组 质地名称 不同土壤类型的 <0,0 1 毫米粒级含量 (% )
灰化土 草原土壤、红黄壤 碱化土、碱土砂土 松砂土紧砂土
0 ～ 5
5 ～ 10
0 ～ 5
5 ～ 10
0 ～ 5
5 ～ 10
壤土 砂壤轻壤中壤重壤
10 ～ 20
20 ～ 30
30 ～ 40
40 ～ 50
10 ～ 20
20 ～ 30
30 ～ 45
45 ～ 60
10 ～ 15
15 ～ 20
20 ～ 30
30 ～ 40
粘土 轻粘土中粘土重粘土
50 ～ 65
65 ～ 80
>80
60 ～ 75
75 ～ 85
>85
40 ～ 50
50 ～ 65
>65
Soil texture
表 4 － 8 中国土壤质地分类
（邓时琴,1 9 8 5 ）
质地组 质地名称 颗粒组成 % （粒径：毫米）
砂粒 (1 -0,0 5) 粗粉粒 (0,0 5-0,01) 细粘粒 (<0,001 )
砂土 极重砂土重砂土中砂土轻砂土
>80
70 ～ 80
60 ～ 70
50 ～ 60
壤土 砂粉土粉土
≥ 20
<20
≥ 40 <30
砂壤壤土
≥ 20
<20
<40
粘土 轻粘土中粘土重粘土极重粘土
30 ～ 35
35 ～ 40
40 ～ 60
>60
Clayed soil
Loamy soil
Sandy soil
The soil texture is divided by three main groups--
sand,silt,and clay in our country.
1,Sand? < 2 mm to > 0.02 mm
Visible without
microscope
Rounded or angular in
shape
Sand grains usually
quartz if sand looks
white or many minerals
if sand looks brown,
Some sands in soil will
be brown,yellow,or red
because of Fe and/or Al
oxide coatings.
三,The fertility characteristics,utilize and improves of different
soil textures
(一 )The fertility characteristics of different soil textures
Sand
Feels gritty
Considered non-
cohesive – does
not stick together
in a mass unless it
is very wet.
Sand
Low specific surface area
Sand has less nutrients for
plants than smaller particles
Voids between sand
particles promote free
drainage and entry of air
Holds little water and prone
to drought
2,Clay
< 0.002 mm
Flat palettes or tiny flakes
Small clay particles are
colloids
– If suspended in water will not
settle
Large surface area
– spoonful = football field
Clay
Wet clay is very sticky
and is plastic or it can
be molded readily into a
shape or rod.
Easily formed into long
ribbons
Shrink and swell
Clay
Pores spaces are very small
– Movement of water and air
very slow
Water holding capacity
– Tremendous capacity to
adsorb water- not all available
for plants.
Soil strength- shrink/swell
affects buildings,roads and
walls.
Chemical adsorption is large
3,Loam
< 0.02 mm to > 0.002 mm
Not visible without
microscope
Quartz often dominant
mineral in loam since
other minerals have
weathered away.
Loam
Does not feel gritty
Floury feel
Wet loam does not
exhibit stickiness /
plasticity / malleability
Loam
Smaller size allows rapid
weathering of non quartz
minerals
Smaller particles – retains
more water for plants and
have slower drainage than
sand.
Easily washed away by
flowing water – highly
erosive.
Holds more plant nutrients
than sand.
Silt is
responsible for
silting over
gravel beds in
rivers that are
needed by fish
for spawning.
Loess Cliff in China
Silt if often left as
a vertical face
since in this
condition the
landscape is less
prone to water
erosion than if the
area was graded to
a slope.
(二） Utilize and improves of different soil textures
① Foreign soil methods
Soil texture can be changed only by
mixing with another soil with a different
textural class in small quantities
② Deep ploughing,deep turn over
etc.
Adding peat or compost to a mineral soil is
not considered changing the texture – since it
only adds organic matter not sand,silt or
clay!!
一,Soil structureness
（一） Concept of soil structure
Soil structure- The combination or arrangement of
primary soil particles into secondary units or peds,The
secondary units are characterized on the basis of size,
shape,and grade (degree of distinctness).
Section 3 Soil Structure
(二 ) Classes and types of soil structure
Types of structure describe the ped shape with the terms
granular,crumb,platy,blocky,subangular blocky,
prismatic,and columnar.
Structure classes are the ped sizes such as very fine,
fine,medium,coarse (or thick),and very coarse (or
very thick).
Soil structureness
Bad structure：
platy,blocky,subangular blocky,prismatic,
and columnar
Good structure:
Granular
二,The genesis of granular structure
(一 ) The formation process of granular structure
1,Cohesion aggregation
① Condense
② Cohesion of inorganic matter
③ Cementation and compound of organic matter
④ Complex of organic-mineral
⑤ Earthworms and other small animals
① Root ② Wetting and drying cycle
③ Alternate freezing and thawing ④ Tillage
2,The process of incision and modelling
The arrangement of soil particle
单个土粒团聚体微团粒
(二） Formation process of
soil aggregates
砂粒砂粒粉粒粉粒粘粒
Humus
土粒土粒土粒
Ca2+
腐殖质土粒土粒土粒
Fe2+
腐殖质
Fe3+
Al3+
1,Clay domain theory
(三 ) Microcosmic mechanism of soil
aggregates formation
2,Isoelectric condense theory
(四 ) Significance of granular
structure in soil fertility
1,There are big and small pores in granular structure
2.Balance to water and air in soil
3.Coordinated to keep and apply fertilizer
4,Suitable tillage
5,Had good plowed layer
(五 ) Management of soil structure
1,Apply organic fertilizer
2,Reasonable crop rotation
3,Reasonable tillage,water management and soil
reclamation
4,Apply soil structure modifier
5,The electric current reclamation of saline-alkali soil
1,Soil porosity = pore volume/soil volume
=(soil volume – soil particle volume)/soil volume
= 1-（ soil particle volume/ soil volume）
= 1-[（ soil particle volume× soil weight） /（ soil
volume× soil weight） ]
= 1-[（ soil weight/ soil volume） × （ soil particle
volume/ soil weight ） ]
=1-[（ soil weight/ soil volume） /（ soil weight /
soil particle volume） ]
= （ 1-bulk density/ density）
Section 4 Soil pores and soil body constitution
一,Soil porosity
(一 ) Calculation of soil porosity
2,Scope of soil porosity
Sandy soil 30－ 45％
Loam soil 40-50%
Clay soil 45-60%
Peaty soil 〉 80％
3,Loose and tight arrangement of soil particles
方体排列的孔度为 47.46%（ 左 ）
三斜六面体排列的孔度为 24.51％ （ 右 ）
(二 ) Grade of soil porosity
1,Capillary porosity
2,Classification of porosity (Studied by yourself)
3,Aeration porosity
二,The porosity model of granular structure
(Studied by yourself)
三,Equivalent pore diameter (effective aperture)
Aeration pores- Greater than 0.1 mm average diameter,
Size of medium sands.
Capillary pores- 0.1-0.03 mm average diameter,Size of silt
particles.
Storage pores-Less than 0.03 mm average diameter,Size of
clay particles.
四,Soil body constitution
(一 ) plowed layer constitution
(二 ) Texture profiles
(三 ) Structure profiles
1,A horizon
2,P horizon
3,W horizon
4,G (gley horizon)
（四） Porosity profiles
The suitable porosity for plant growth:
Plowed layer soil,total porosity in 50% to 56%,
aeration pores in 8% to 10%.
1,团粒结构在土壤肥力方面作用和意义有哪些?
2,为什么说粒状 ——团粒状结构是农业生产上比较理想的结构?培育良好结构的有效途径是什么?
二、思考题
Soil texture and structure
Section 1
Soil three phases Constitution
一,Soil density and bulk density
（ 一 ） Soil density ( or Particle density)
Soil density is the density of the solid soil particles only; the
measurement does not include water weight or pore (air) space,The
dominant soil minerals- quartz,feldspars,micas,and clay minerals-
average approximately 2.65 g/cm3,the,standard” value used in
calculations if particle density is not measured.
Individual minerals have densities from 2.0 g/cm3 for bauxite
(aluminum ore) to 5.3 for hematite (iron ore) or 7.6 for galena (lead
ore).
表 4 － 2 一种森林土壤表层各级土粒的密度粒级 （粒径毫米） 腐殖质 （克 / 千克 ) 密度 ( 克 / 厘米
3
)
全土样
0,1 0 ～ 0,0 5
0,0 5 ～ 0,0 1
0,0 1 ～ 0,0 0 5
0,0 0 5 ～ 0,0 0 1
< 0,0 0 1
2 9,5
0
4,3
1 4,8
5 3,7
6 4,2
2,6 2
2,6 6
2,6 6
2,6 2
2,5 9
2,5 9
表 4 - 1 土壤中常见组分的密度 ( 克 / 厘米
3
)
石 英正长石斜长石白云母黑云母角闪石辉 石纤铁矿
2,6 0 ～ 2,6 8
2,5 4 ～ 2,5 7
2,6 2 ～ 2,7 6
2,7 7 ～ 2,8 8
2,7 0 ～ 3,1 0
2,8 5 ～ 3,5 7
3,1 5 ～ 3,9 0
3,6 0 ～ 4,1 0
赤铁矿磁铁矿三水铝石高岭石蒙皂石伊利石腐殖质
4,9 0 ～ 5,3 0
5,0 3 ～ 5,1 8
2,3 0 ～ 2,4 0
2,6 1 ～ 2,6 8
2,5 3 ～ 2,7 4
2,6 0 ～ 2,9 0
1,4 0 ～ 1,8 0
（ 二 ） Soil bulk density
1,Bulk density,the density for a volume of soil as it exists
naturally,includes any air space and organic materials in the
soil volume.
ρb = (mass of dry soil)/(total volume of soil) = Ms/Vt
= Ms/(Vs + Vw +Va)
A recently cultivated topsoil is likely to have a bulk density
in the range from 0.9 to 1.2 g/cm3,while a compact subsoil may
have a bulk density of 1.6 g/cm3 or even more.
Uses of soil bulk density：
① To calculate soil porosity(p0):
② To calculate soil weight
③ To calculate storage of soil compositions
④ To calculate total water storage capacity
and irrigation (or drainage) quota.
2,Bulk density in water
= (soil mass over-dry)/(precipitation volume)
3,Affect the factors of soil bulk density:
Texture,structure,content of organic matter,and various
nature factors and anthropogenic factors.
P0 = 1- (Bulk density/soil density)
(一 ),Soil three phases constitution and porosity
二,Soil three phases constitution and pore
小孔隙大孔隙
1,Index three phases constitution
Solid phase (%) =（ solid volume /soil body volume) × 100
Liquid phase (%) =（ liquid volume /soil body volume) × 100
Gas phase (%) =（ air volume /soil body volume) × 100
2,Soil porosity:
Soil porosity is the percentage of the volume of pores to
the total volume of soil.
Soil porosity ＝ 1－ Solid phase (%)
= Liquid phase (%) + Gas phase (%)
The void ratio is the ratio of the volume of pores to the volume of
solids.
Void ratio = (volume of pores)/(volume of solids)
(二 ),Calculation of three phases constitution and porosity
1,Solid ratio
Solid ratio =（ bulk density /density） = ρb/ ρp
2,Liquid ratio (volumetric water content)
θm = (mass of water /mass of dry soil) = MW/MS
θv = (volume of water/ total volume of soil) = Vw/Vt
= Vw/(Vs+Vw+Va) = θm × ρb
3,Void ratio
3,Gas phase ratio
Porosity(P0) =1- solid phase ratio =1- bulk density /density）
= ρb/ ρp
Gas phase ratio = porosity- volumetric water content = P0- θv
4,Actual volume ratio
Solid phase ratio ＝ actual volume ratio－ volumetric water content
Gas phase ratio = 1－ actual volume ratio
Soil three phases ratio
＝ solid phase ratio,volumetric water content,gas phase ratio
(三 ),Suitable soil three phases ratio：
Solid phase ratio is about 50%，
volumetric water content is 25% to 30%，
Gas phase ratio is 15% to 25%.
(一 ) Types of soil particle：
Mineral soil particle and organic soil particle
Single particle and compound particle
Primary particle and second particle
(二 ) Soil particle fraction (soil separates)
Natural soils are comprised of soil particles of varying
sizes,The soil particle-size groups,called soil particle
fraction (soil separates),are sands (the coarsest),silts,
and clays (the smallest).
一,Soil particle and particle fraction (soil separates)
Section 2 Soil texture
Particle Diameter Size
Soil particle diameters
range over 4 orders of
magnitude
– Boulders
– Sand
– Silt
– Clay
Physical sandy particle,
1 mm to 0.01 mm.
Physical clay particle,
< 0.01 mm
Kachinsky classification system of soil separates
Soil particle
Classification system of soil separates,(mm)
Diameter International USDA Kachinsky Chinese
Boulders >2 >2 > 1 >1
Sand 2-0.02 2-0.05 1-0.05 1-0.05
Silt 0.02-0.002 0.05-0.002 0.05-0.001 0.05-0.002
Clay 〈 0.002 〈 0.002 〈 0.001 〈 0.002
(一 ） Soil mechanical composition
（ 二 ） Soil texture
1.Concept,Soil texture-The relative proportions of the
various soil separates in a soil.
2,Classification of soil texture
二,Soil mechanical composition and texture
(1) International classification：
The textural triangle is used to determine the soil textural
name after the percentages of sand (2-0.02mm),silt (0.02-0.002
mm),and clay (<0.002 mm) are determined from a laboratory
analysis.
The main criterion of classification：
Clay <15% is sand and loamy groups;
15％－ 25％ is clay loam group;
>25% is clay group.
When soil contains silt >45%,soil will be called,silty” ；
When soil contains sand in 55%-85%,called,sandy”,
When soil contains sand >85%,called,loamy sand”or,sand”.
The U.S,Dept,of Agri,(USDA)
Soil texture
表 4 － 6 卡钦斯基土壤质地基本分类 （简制）
质地组 质地名称 不同土壤类型的 <0,0 1 毫米粒级含量 (% )
灰化土 草原土壤、红黄壤 碱化土、碱土砂土 松砂土紧砂土
0 ～ 5
5 ～ 10
0 ～ 5
5 ～ 10
0 ～ 5
5 ～ 10
壤土 砂壤轻壤中壤重壤
10 ～ 20
20 ～ 30
30 ～ 40
40 ～ 50
10 ～ 20
20 ～ 30
30 ～ 45
45 ～ 60
10 ～ 15
15 ～ 20
20 ～ 30
30 ～ 40
粘土 轻粘土中粘土重粘土
50 ～ 65
65 ～ 80
>80
60 ～ 75
75 ～ 85
>85
40 ～ 50
50 ～ 65
>65
Soil texture
表 4 － 8 中国土壤质地分类
（邓时琴,1 9 8 5 ）
质地组 质地名称 颗粒组成 % （粒径：毫米）
砂粒 (1 -0,0 5) 粗粉粒 (0,0 5-0,01) 细粘粒 (<0,001 )
砂土 极重砂土重砂土中砂土轻砂土
>80
70 ～ 80
60 ～ 70
50 ～ 60
壤土 砂粉土粉土
≥ 20
<20
≥ 40 <30
砂壤壤土
≥ 20
<20
<40
粘土 轻粘土中粘土重粘土极重粘土
30 ～ 35
35 ～ 40
40 ～ 60
>60
Clayed soil
Loamy soil
Sandy soil
The soil texture is divided by three main groups--
sand,silt,and clay in our country.
1,Sand? < 2 mm to > 0.02 mm
Visible without
microscope
Rounded or angular in
shape
Sand grains usually
quartz if sand looks
white or many minerals
if sand looks brown,
Some sands in soil will
be brown,yellow,or red
because of Fe and/or Al
oxide coatings.
三,The fertility characteristics,utilize and improves of different
soil textures
(一 )The fertility characteristics of different soil textures
Sand
Feels gritty
Considered non-
cohesive – does
not stick together
in a mass unless it
is very wet.
Sand
Low specific surface area
Sand has less nutrients for
plants than smaller particles
Voids between sand
particles promote free
drainage and entry of air
Holds little water and prone
to drought
2,Clay
< 0.002 mm
Flat palettes or tiny flakes
Small clay particles are
colloids
– If suspended in water will not
settle
Large surface area
– spoonful = football field
Clay
Wet clay is very sticky
and is plastic or it can
be molded readily into a
shape or rod.
Easily formed into long
ribbons
Shrink and swell
Clay
Pores spaces are very small
– Movement of water and air
very slow
Water holding capacity
– Tremendous capacity to
adsorb water- not all available
for plants.
Soil strength- shrink/swell
affects buildings,roads and
walls.
Chemical adsorption is large
3,Loam
< 0.02 mm to > 0.002 mm
Not visible without
microscope
Quartz often dominant
mineral in loam since
other minerals have
weathered away.
Loam
Does not feel gritty
Floury feel
Wet loam does not
exhibit stickiness /
plasticity / malleability
Loam
Smaller size allows rapid
weathering of non quartz
minerals
Smaller particles – retains
more water for plants and
have slower drainage than
sand.
Easily washed away by
flowing water – highly
erosive.
Holds more plant nutrients
than sand.
Silt is
responsible for
silting over
gravel beds in
rivers that are
needed by fish
for spawning.
Loess Cliff in China
Silt if often left as
a vertical face
since in this
condition the
landscape is less
prone to water
erosion than if the
area was graded to
a slope.
(二） Utilize and improves of different soil textures
① Foreign soil methods
Soil texture can be changed only by
mixing with another soil with a different
textural class in small quantities
② Deep ploughing,deep turn over
etc.
Adding peat or compost to a mineral soil is
not considered changing the texture – since it
only adds organic matter not sand,silt or
clay!!
一,Soil structureness
（一） Concept of soil structure
Soil structure- The combination or arrangement of
primary soil particles into secondary units or peds,The
secondary units are characterized on the basis of size,
shape,and grade (degree of distinctness).
Section 3 Soil Structure
(二 ) Classes and types of soil structure
Types of structure describe the ped shape with the terms
granular,crumb,platy,blocky,subangular blocky,
prismatic,and columnar.
Structure classes are the ped sizes such as very fine,
fine,medium,coarse (or thick),and very coarse (or
very thick).
Soil structureness
Bad structure：
platy,blocky,subangular blocky,prismatic,
and columnar
Good structure:
Granular
二,The genesis of granular structure
(一 ) The formation process of granular structure
1,Cohesion aggregation
① Condense
② Cohesion of inorganic matter
③ Cementation and compound of organic matter
④ Complex of organic-mineral
⑤ Earthworms and other small animals
① Root ② Wetting and drying cycle
③ Alternate freezing and thawing ④ Tillage
2,The process of incision and modelling
The arrangement of soil particle
单个土粒团聚体微团粒
(二） Formation process of
soil aggregates
砂粒砂粒粉粒粉粒粘粒
Humus
土粒土粒土粒
Ca2+
腐殖质土粒土粒土粒
Fe2+
腐殖质
Fe3+
Al3+
1,Clay domain theory
(三 ) Microcosmic mechanism of soil
aggregates formation
2,Isoelectric condense theory
(四 ) Significance of granular
structure in soil fertility
1,There are big and small pores in granular structure
2.Balance to water and air in soil
3.Coordinated to keep and apply fertilizer
4,Suitable tillage
5,Had good plowed layer
(五 ) Management of soil structure
1,Apply organic fertilizer
2,Reasonable crop rotation
3,Reasonable tillage,water management and soil
reclamation
4,Apply soil structure modifier
5,The electric current reclamation of saline-alkali soil
1,Soil porosity = pore volume/soil volume
=(soil volume – soil particle volume)/soil volume
= 1-（ soil particle volume/ soil volume）
= 1-[（ soil particle volume× soil weight） /（ soil
volume× soil weight） ]
= 1-[（ soil weight/ soil volume） × （ soil particle
volume/ soil weight ） ]
=1-[（ soil weight/ soil volume） /（ soil weight /
soil particle volume） ]
= （ 1-bulk density/ density）
Section 4 Soil pores and soil body constitution
一,Soil porosity
(一 ) Calculation of soil porosity
2,Scope of soil porosity
Sandy soil 30－ 45％
Loam soil 40-50%
Clay soil 45-60%
Peaty soil 〉 80％
3,Loose and tight arrangement of soil particles
方体排列的孔度为 47.46%（ 左 ）
三斜六面体排列的孔度为 24.51％ （ 右 ）
(二 ) Grade of soil porosity
1,Capillary porosity
2,Classification of porosity (Studied by yourself)
3,Aeration porosity
二,The porosity model of granular structure
(Studied by yourself)
三,Equivalent pore diameter (effective aperture)
Aeration pores- Greater than 0.1 mm average diameter,
Size of medium sands.
Capillary pores- 0.1-0.03 mm average diameter,Size of silt
particles.
Storage pores-Less than 0.03 mm average diameter,Size of
clay particles.
四,Soil body constitution
(一 ) plowed layer constitution
(二 ) Texture profiles
(三 ) Structure profiles
1,A horizon
2,P horizon
3,W horizon
4,G (gley horizon)
（四） Porosity profiles
The suitable porosity for plant growth:
Plowed layer soil,total porosity in 50% to 56%,
aeration pores in 8% to 10%.
1,团粒结构在土壤肥力方面作用和意义有哪些?
2,为什么说粒状 ——团粒状结构是农业生产上比较理想的结构?培育良好结构的有效途径是什么?
二、思考题
