1. Medium for Plant growth

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The Functions of Soil

• 1. Medium for Plant growth
• provides anchorage
• ventilation, soil pores allow CO2, formed
  through root respiration escape to the atmosphere
  and O2 to be  replenished
• absorption and storage of water
• temperature modification
• supplies nutrients
•             Essential Elements
•             C, H, O - supplied mostly from air
  and water
•             N, P, K, Ca, Mg, S, Fe, Mn, B, Zn,
  Cu, Cl, Co, Mo, Ni - supplied by the soil
•            

2
The Functions of Soil

•  2.  Regulator of water supplies
• There is a growing concern over the quality of
  the nations water supplies and increasing
  awareness of the relation between soil and water
  quality. 
• Remember that almost every drop of water in our
  river, lakes, estuaries and aquifers has traveled
  through or over the soil at some point in time.
• storage of water
• water purification/filtration

3
The Functions of Soil
 3.  Recycler of raw materials - soil processes
take great quantities of organic waste and
recycle it to plant available forms.  The
recycling of plant material (decomposition)
returns C in the form of CO2 to the atmosphere. 
In this capacity, soils play a large role in
global cycles and are important to issues such as
the Greenhouse Effect.  
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The Functions of Soil

• 4.  Habitat for soil organisms
• a handful of soil may be home to billons of
  organisms belonging to a thousand species
• soils harbor much of the world's genetic
  diversity
• provides niches

 5.  Engineering medium Reliable construction
requires knowledge of the diversity and
variability of soil properties across time and
space.
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The Functions of Soil

• 1. Medium for Plant growth
• provides anchorage
• ventilation, soil pores allow CO2, formed
  through root respiration escape to the atmosphere
  and O2 to be  replenished
• absorption and storage of water
• temperature modification
• supplies nutrients
•             Essential Elements
•             C, H, O - supplied mostly from air
  and water
•             N, P, K, Ca, Mg, S, Fe, Mn, B, Zn,
  Cu, Cl, Co, Mo, Ni - supplied by the soil
•            

8
The Functions of Soil

•  2.  Regulator of water supplies
• There is a growing concern over the quality of
  the nations water supplies and increasing
  awareness of the relation between soil and water
  quality. 
• Remember that almost every drop of water in our
  river, lakes, estuaries and aquifers has traveled
  through or over the soil at some point in time.
• storage of water
• water purification/filtration

9
The Functions of Soil
 3.  Recycler of raw materials - soil processes
take great quantities of organic waste and
recycle it to plant available forms.  The
recycling of plant material (decomposition)
returns C in the form of CO2 to the atmosphere. 
In this capacity, soils play a large role in
global cycles and are important to issues such as
the Greenhouse Effect.  
10
The Functions of Soil

• 4.  Habitat for soil organisms
• a handful of soil may be home to billons of
  organisms belonging to a thousand species
• soils harbor much of the world's genetic
  diversity
• provides niches

 5.  Engineering medium Reliable construction
requires knowledge of the diversity and
variability of soil properties across time and
space.
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• 0.2 20
• 25 1 25
• 25 20 45 /125 0. 36

48-30/48 100 37.5
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Mass water content is a ratio of water mass to
dry soil mass
Example A moist soil weighs 120 g.when dried
the soil weighs 100 g. the water mass was 20
g.         Therefore, ?m 20 g water/100 g
soil 0.20
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???? ????? ???? ?? ??? 385 ??? ?? ??? ? ??????
?? ?? ?? ??? ?? ?? 315 ??? ????? ???? ?? ???. .
??? ??? ????? ??? ??? 35/1 ??? ?? ????? ??? ????
???? ?????? ???? ? ???? ????? ?? ???? ????? .
70/315 0.22
0.22 100 22 ????? ????
0.22 1.35 0.297 ????? ????
0.297 100 29.7 ???? ????
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???? ????? ???? ?? ???? 25/0 ??? ? ??? ?????
????? 4/1 ??? ?? ????? ??? ???? ??? . ??????
????? ?? ?? ??? ??? ???? ????
1.4 0.25 0.35 ????? ????
??? ??? ??? ?? ????? ????
0.35 1000 350 mm ??? ??
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???? ??????? ?? ?? ??? ?????
??? - ??? ?? ?? ??? 30 ????????? ??? ???? ????
dw ?v ds
?v ?m Bd
dw 0.234 30
?v 0.18 1.3
?v 0.234 or 23.4
dw 7 cm
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? - ??? ??? ??????? ???? 8/2 ???????? ?? ??
?????? ?? ???? ?? ??? ?? ????? ?? ????
????? ????? ?? ?????? ?? ????
?m ?mfc ?m ?
dw ?v ds
?m 0.23 0.18 ?
ds dw / ?v
?m 0.05 ?
?v ? ?m Bd
ds 2.8 / 0.065
?v 0.05 1.3
ds 43 cm
?v 0.065
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?- ?? ???? ??????? ?? ??? 30 ????????? ???? ?????
?? ????? ????? ???? ???? ????
dw ?v ds
dw ?m . Bd ds
dw (?mfc ?mpwp) . Bd ds
dw (0.23 0.09) 1.3 30
dw 5.47 cm
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?? ?? ????? ???? ????? ??? ?? ?? ????????? ?????
?? ???? ? ?? ??? ??????? ???? ?? ?????
30 ???? ????? ??? 1 ??? 20 ???? ????? ???
5 ??? 10 ???? ????? ??? 10 ??? 5
????? ????? ?? ??????? ?? ??? ?? ????
???
?????
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?????? ??? ?? ?? ???? ????? ??? ???
??????? ?? ?? ?? ?? ???? ?????? ???? ???? ????
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???.
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The fast neutrons are emitted in all directions,
where they collide with atoms in the soil.
Through repeated collisions, they are scattered
and some lose part of their energy. As the energy
is lost, the neutrons are slowed to a speed of
about 1.7 miles per second. Neutrons that have
been slowed are said to be "thermalized" and are
called "slow neutrons." The neutron detector in
the neutron moisture meter is designed to ignore
fast neutrons and count only thermalized or slow
neutrons. The average energy in a collision with
another atom is much greater with atoms of low
atomic weight than in collisions involving
heavier atoms. Hydrogen is the only element with
a low atomic weight that is found in significant
amounts in typical soils. Hydrogen found in soils
is almost entirely in the form of water. The
occurrence of hydrogen in water allows for the
use of the neutron probe to measure soil water
content.
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?v Rs / Rstd b-j
?????
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??? ???
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?? ?? ????? ???? ?????? ?? ?? ???? ??? ????? ??
???? ? ?? ??? ??????? ???? ?? ?????
30 ???? ????? 100 ??? 20 ???? ????? 100
??? 10 ???? ????? 500 ???
????? ????? ?? ??????? ?? ??? ?? ????
?????? ?? ???
?????
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Colloidal Properties
1. Size - extremely small 2. Surface area - very
large 3. Surface charge (a) most soils
electronegative charge dominates (b) results in
ion (cation) adsorption
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Types of Colloids
1. Layer silicate clays
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2- Hydrous oxides of Fe and Al
(a) highly weathered soils coatings (b) some
have structure, others poorly structured (c)
examples gibbsite, Al(OH)3 goethite, FeOOH
3-Allophane and other amorphous minerals
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4. Organic colloids
(a) highly charged (pH dependant) (b) phenolic
and carboxyl OH groups
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Adsorbed cations
(a) arid region soils "basic" cations Ca2,
Mg2, K, Na (b) humid region soils "acidic"
cations as well Ca2, Mg2, H and Al3 (c)
strength of adsorption Al3gt Ca2 Mg2 gt K
NH4 gt Na
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??????? ???? ??? ?????
O? Si?? ????? ????? ??? 75 ??? ????? ? ????
???? ??????? ???? ?? ?? ?????.
?????? ? 4?????? ? ?? ?????? ?? ???? ???? ????
?????????? ?? ?? ???? ?? ?????.
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O
Si
SiO4-
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C. Layer Silicate Clay Structure- basic building
blocks 1. Tetrahedron - SiO4
Sharing of O or OH groups sheets and unit
layers (a) tetrahedral sheet                      
    
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2. Octahedron - Al(OH)6
octahedral sheet  
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Tetrahedral and octahedral sheets are often drawn
as shown below   
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11 Type Minerals 1. Mostly, kaolinite    
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Unit layers H-bonded together     è "fixed
lattice type" ü no interlayer activity ü no
shrink-swell ü only external surface 3. Well
crystallized (a) little isomorphous
substitution ü low cation adsorption (b) larger
particle size (0.1 - 5 m m) - hexagonal shaped
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Type Minerals 1. Expanding lattice (a) Smectite
group (mostly, montmorillonite) 
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    (b) Freely expanding water in interlayer
large shrink-swell adsorbed cations in
interlayer - offset the isomorphous
substitution large internal surface (c) Poorly
crystallized small size isomorphous
substitution large cation adsorption
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Vermiculite similar to smectites except Al3
for Si4 in tetrahedral layer interlayer ions
are more structured (Mg2 H2O) limited
expansion large cation adsorption
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Non-expanding lattice (a) Fine-grained micas or
illite
Al3 and K substitute for Si4 (tetrahedral
sheet) u weathering at edges release of K -
very limited expansion - medium cation adsorption
- limited internal surface - properties between
kaolinite and vermiculite
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Chlorites u Mg-octahedral sheet replace K of
illite u properties similar to illite
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Summary of Properties
    Surface Area (m2/g) Surface Area (m2/g) Interlayer Cation
  Size (mm) External Internal Spacing (nm) Sorption
Kaolinite 0.1-5.0 10-50 - 0.7 5-15
Smectite lt1.0 70-150 500-700 1.0-2.0 85-110
Vermiculite 0.1- 5.0 50-100 450-600 1.0-1.4 100-120
Illite 0.1-2.0 50-100 5-100 1.0 15-40
Humus coatings - - - 100-300
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Clay Genesis and Distribution 1. Stages of
weathering (a) alkali metals and alkaline earths
dissolve (Na, K, Ca2, Mg2) (b) Si dissolves
and leaches (c) continual reforming of new clay
minerals
Clays reflect weathering processes Young, weakly
weathered soils fine-grained mica, chlorite,
vermiculite Intermediate weathering
vermiculite, smectite, kaolinite Strong
weathering kaolinite, hydrous oxides