Soil Structure & Aggregation

frizzflowerΠολεοδομικά Έργα

29 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

802 εμφανίσεις

STRUKTUR TANAH

DAN

AGREGASI

(
Soemarno
,
Maret

2012)

FOTO: smno.kampus.ub.jan2013

Mengapa

jalan

aspal

ini

retak
-
retak
?

STRUKTUR TANAH

Sumber: http://www.soils.wisc.edu/courses/SS325/morphology.htm#structure …..
Diunduh 10/3/2012

Structure refers to the arrangement of soil particles. Soil
structure is the product of processes that aggregate, cement,
compact or unconsolidate soil material. In essence, soil
structure is a physical condition that is distinct from that of the
initial material from which it formed, and can be related to
processes of soil formation.

The peds are separated from the adjoining peds by surfaces
of weakness. To describe structure in a soil profile it is best to
examine the profile standing some meters apart to recognize
larger structural units (e.g. prisms).


The next step is to study the
structure by removing soil material
for more detailed inspection. It
should be stressed that soil
moisture affects the expression of
soil structure. The classification of
soil structure considers the grade,
form, and size of particles.



Sumber: http://www.soils.wisc.edu/courses/SS325/morphology.htm#structure …..
Diunduh 10/3/2012

The
grade

describes the distinctiveness of the peds
(differential between cohesion within peds and adhesion
between peds). It relates to the degree of aggregation or the
develoment of soil structure. In the field a classification of
grade is based on a finger test (durability of peds) or a
crushing of a soil sample.


The
form

is classified on the basis of the shape of peds, such
as spheroidal, platy, blocky, or prismatic. A granular or crumb
structure is often found in A horizons, a platy structure in E
horizons, and a blocky, prismatic or columnar structure in Bt
horizons. Massive or single
-
grain structure occurs in very
young soils, which are in an initial stage of soil development.
Another example where massive or single
-
grain structure can
be identified is on reconstruction sites. There may two or
more structural arrangements occur in a given profile. This
may be in the form of progressive change in size/type of
structural units with depth (e.g. A horizons that exhibit a
progressive increase in size of granular peds that grade into
subangular blocks with increasing depth) or occurrence of
larger structural entities (e.g. prisms) that are internally
composed of smaller structural units (e.g. blocky peds). I such
a case all discernible structures should be recorded (i.e. more
rather than less detail).


The
size

of the particles have to be recorded as well, which is
dependent on the form of the peds.

GRADE STRUKTUR TANAH

Classification of
soil structure
considering
grade, size, and
form of particles.

Grade


Abbreviat
ion


Description


Structureless

0

No observable aggregation or no
orderly arrangement of natural
lines of weakness

Weak

1

Poorly formed indistinct peds

Moderate

2

Well
-
formed distinct peds,
moderately durable and evident,
but not distinct in undisturbed soil

Strong

3

Durable
peds

that are quite
evident in
undisplaced

soil, adhere
weakly to one another, withstand
displacement, and become
separated when soil is disturbed

Sumber: http://www.soils.wisc.edu/courses/SS325/morphology.htm#structure …..
Diunduh 10/3/2012

BENTUK STRUKTUR

Form


Abbreviation


Description


Granular

gr

Relatively nonporous, spheroidal peds, not fitted
to adjoining peds

Crumb

cr

Relatively porous, spheroidal peds, not fitted to
adjoining peds

Platy

pl

Peds are plate
-
like. The particles are arranged
about a horizontal plane with limited vertical
development. Plates often overlap and impair
permeability

Blocky

bk

Block
-
like peds bounded by other peds whose
sharp angular faces form the cast for the ped.
The peds often break into smaller blocky peds

Angular blocky

abk

Block
-
like peds bounded by other peds whose
sharp angular faces form the cast for the ped

Subangular
blocky

sbk

Block
-
like peds bounded by other peds whose
rounded subangular faces form the cast for the
ped

Prismatic

pr

Column
-
like peds without rounded caps. Other
prismatic caps form the cast for the ped. Some
prismatic peds break into smaller blocky peds.
In these peds the horizontal development is
limited when compared with the vertical

Columnar

cpr

Column
-
like peds with rounded caps bounded
laterally by other peds that form the cast for the
peds. In these peds the horizontal development
is limited when compared with the vertical

Single grain

sg

Particles show little or no tendency to adhere to
other particles. Often associated with very
coarse particles

Massive

m

A massive structure show little or no tendency
to break apart under light pressure into smaller
units. Often associated with very fine
-
textured
soils.

Sumber: http://www.soils.wisc.edu/courses/SS325/morphology.htm#structure …..
Diunduh 10/3/2012

UKURAN STRUKTUR

Size


Angular
and
subangula
r blocky
structure

[mm]
diameter

Granular
and
crumb
structure

[mm]
diameter

Platy
structure

[mm] width

Prismatic
and
columnar
structure

[mm]
diameter

Very fine

< 5

< 1

< 1 (very
thin)

< 10

Fine

5
-

10

1
-

2

1
-

2 (thin)

10
-

20

Medium

10
-

20

2
-

5

2
-

5

20
-

50

Coarse

20
-

50

5
-

10

5
-

10
(thick)

50
-

100

Very
coarse

> 50

> 10

> 10 (very
thick)

> 100

Sumber: http://www.soils.wisc.edu/courses/SS325/morphology.htm#structure …..
Diunduh 10/3/2012

STRUKTUR TANAH

Sumber: ….. Dunduh 10/3/2012

The three characteristics of soil structure are conventionally
written in the order grade, size, and shape.


For example, weak fine subangular blocky structure.




The distribution of different particle sizes in a soil influence
the distribution of pores, which can be characterized by their
abundance, size, and shape.

Abundance


Per unit area


Few

< 1

Common

1
-

5

Many

> 5

Size


Diameter (mm)


Very fine

< 0.5

Fine

0.5
-

2.0

Medium

2.0
-

5.0

Coarse

> 5.0

Shape


Vesicular approx. spherical or elliptical

Tubular approx. cylindrical or elongated

Irregularly shaped

Sumber: http://www.soils.wisc.edu/courses/SS325/morphology.htm#structure …..
Diunduh 10/3/2012

Significance of Soil Structure


Soil formation starts with a structureless condition, i.e., the
structure is single
-
grained or massive. Soil development also
means development of soil structure, which describes the
formation of peds and aggregates. Soil structure forms due to
the action of forces that push soil particles together.
Subsurface structure tends to be composed of larger
structural units than the surface structure. Subsoil structure
also tend to have the binding agents on ped surfaces rather
than mixed throughout the ped.


Climatically
-
driven physical processes that result in changes
in the amount, distribution and phase (solid, liquid, vapor) of
water exert a major influence on formation of soil structure.
Phase changes (shrinking
-
swelling, freezing
-
thawing) result in
volume changes in the soil, which over time produces distinct
aggregations of soil materials.


Physico
-
chemical processes (e.g., freeze
-
thaw, wet
-
dry, clay
translocation, formation/removal of pedogenic weathering
products) influence soil structure formation through out the
profile. However, the nature and intensity of these processes
varies with depth below the ground surface. The structure and
hydrological function of plant communities, texture,
mineralogy, surface manipulation and topography all serve to
modify local climatic effects through their influence on
infiltration, storage and evapotranspiration of water.


Sumber: http://www.soils.wisc.edu/courses/SS325/morphology.htm#structure …..
Diunduh 10/3/2012

Significance of Soil Structure

Biological processes exert a particularly strong
influence on formation of structure in surface horizons.
The incorporation of soil organic matter is usually
largest in surface horizons. Soil organic matter serves
as an agent for building soil aggregates, particularly the
polysaccharides appear to be responsible for the
formation of peds.


Plant roots exert compactive stresses on surrounding
soil material, which promotes structure formation.



Soil
-
dwelling animals
(e.g., earth worms,
gophers) also exert
compactive forces, and in
some cases (e.g., earth
worms) further contribute
to structure formation via
ingestion/excretion of soil
material that includes
incorporated organic
secretions.

Sumber: http://www.soils.wisc.edu/courses/SS325/morphology.htm#structure …..
Diunduh 10/3/2012

KONSISTENSI TANAH



Consistence refers to the cohesion among soil particles and
adhesion of soil to other substances or the resistence of the
soil to deformation. Whereas soil structure deals with the
arrangement and form of peds, consistence deals with the
strength and nature of the forces between particles.


Consistence is described for three moisture levels: wet, moist,
and dry.


Sumber: http://www.soils.wisc.edu/courses/SS325/morphology.htm#structure …..
Diunduh 10/3/2012

The stickiness describes the quality of adhesion
to other objects and the plasticity the capability
of being molded by hands. Wet consistence is
when the moisture content is at or slightly more
than field capacity. Moist consistence is a soil
moisture content between field capacity and the
permanent wilting point. When recording
consistence it is important to record the moisture
status as well. Cementation is also considered
when consistence is described in the field.
Cementing agents are calcium carbonate, silica,
oxides of iron and aluminium.

Sumber: Buol S.W., Hole F.D., McCracken R.J., and Southard R.J., 1997. Soil
Genesis and Classification. Iowa State University Press.
http://www.soils.wisc.edu/courses/SS325/morphology.htm#structure….. Diunduh
10/3/2012

Classification of consistence (Buol et al., 1997).

Moisture
status


Consistence


Abbreviatio
n


Description


wet

Nonsticky

wso

Almost no natural adhesion of soil material
to fingers

Slightly sticky

wss

Soil material adheres to only one finger

Sticky

ws

Soil material adheres to both fingers

Very sticky

wvs

Soil material strongly adheres to both
fingers

Nonplastic

wpo

No wire is formable by rolling material
between the hands

Slightly plastic

wps

Only short (< 1cm) wires are formed by
rolling material between the hands

Plastic

wp

Long wires (>1cm) can be formed and
moderate pressure is needed to deform a
block of the molded material

Very plastic

wvp

Much pressure is needed to deform a
block of the molded material




Moist

Loose

ml

Soil material is noncoherent

Very friable

mvfr

Aggregates crush easily between thumb
and finger

Friable

mfr

Gentle pressure is required to crush
aggregates

Firm

mfi

Moderate pressure is required to crush
aggregates

Very firm

mvfi

Strong pressure is required to crush
aggregates

Extremely firm

mefi

Aggregates cannot be broken by pressure

Dry

Loose

dl

Soft

ds

Slightly hard

dsh

Hard

dh

Very hard

dvh

Extremely hard

deh

Cementati
on

Weakly cemented

cw

Strongly cemented

cs

Indurated


ci


Soil Structure & Aggregation

Soil may be a loose assemblage of individual and random
particles, or consist of distinctly structured
aggregates

of
distinctive size and shape; the particular arrangement of
which is called
soil structure
.

Most methods of measurement are indirect, and measure
various properties that are dependent or at the least
influenced by specific structural properties; e.g., total
porosity, pore size distribution, liquid
retention/transmission, and infiltration.

http://en.wikipedia.org/wiki/Soil_structure ….. Diunduh 28/2/2012

Soil structure

is determined by how
individual soil
granules

clump or bind
together and aggregate, and therefore,
the arrangement of soil pores between
them. Soil structure has a major influence
on water and air movement, biological
activity, root growth and seedling
emergence.

Soils may be non
-
structured (e.g., single
grain or massive) or consist of naturally
formed units known as
peds

or
aggregates
.

The initial stage in the formation of soil
structure is the process of
flocculation
.

Individual colloids typically exhibit a net
negative charge which results in an electrostatic
repulsion.

….. Diunduh 28/2/2012

Reduction of the forces of electrostatic repulsion allows the
particles to come closer together.

Flocculation

This process allows other forces of
attraction to become more dominant. The
formation of these “
flocs
” in suspension
represents the early stages of aggregation.

….. Diunduh 28/2/2012

INTERAKSI LIAT DAN AIR

….. Diunduh 28/2/2012

Clay
-
water interaction

is an all
-
inclusive term to describe
various progressive interactions between
clay minerals

and
water
. In the dry state, clay packets exist in face
-
to
-
face
stacks like a deck of playing cards, but clay packets begin to
change when exposed to water.


Five descriptive terms describe the progressive interactions
that can occur in a clay
-
water system, such as a water mud.


1.
Hydration

occurs as clay packets absorb water and swell.

2.
Dispersion

(or disaggregation) causes clay platelets to
break apart and disperse into the water due to loss of
attractive forces as water forces the platelets farther apart.

3.
Flocculation

begins when mechanical shearing stops and
platelets previously dispersed come together due to the
attractive force of surface charges on the platelets.

4.
Deflocculation
, the opposite effect, occurs by addition of
chemical
deflocculant

to flocculated mud; the positive
edge charges are covered and attraction forces are greatly
reduced.

5.
Aggregation
, a result of ionic or thermal conditions, alters
the
hydrational

layer around clay platelets, removes the
deflocculant

from positive edge charges and allows
platelets to assume a face
-
to
-
face structure.

HIDRASI MINERAL

….. Diunduh 28/2/2012

Mineral hydration

is an inorganic chemical reaction where
water is added to the
crystal structure

of a
mineral
, usually
creating a new mineral, usually called a
hydrate
.


In
geological

terms, the process of mineral hydration is known
as
retrograde alteration

and is a process occurring in
retrograde metamorphism
. It commonly accompanies
metasomatism

and is often a feature of wall rock alteration
around ore bodies. Hydration of minerals occurs generally in
concert with
hydrothermal circulation

which may be driven by
tectonic or igneous activity.


Mineral hydration is also a process in the
regolith

that results
in conversion of silicate minerals into
clay

minerals.

There are two main ways in which minerals hydrate. One is
conversion of an
oxide

to a double
hydroxide
, as with the
hydration of
calcium oxide

-

CaO
-

to
calcium hydroxide

-

Ca(OH)
2
, the other is with the incorporation of water
molecules directly into the crystalline structure of a new
mineral, as in the hydration of
feldspars

to
clay minerals
,
garnet

to
chlorite

or
kyanite

to
muscovite
.


Some mineral structures, for example,
montmorillonite
, are
capable of including a variable amount of water without
significant change to the mineral structure.

Hydration is the mechanism by which
Portland cement

develops strength.

DISPERSI

….. Diunduh 28/2/2012

A
dispersion

is a system in which particles are dispersed in a continuous
phase of a different composition (or state).

A dispersion is classified in a number of different ways, including how
large the particles are in relation to the particles of the continuous phase,
whether or not
precipitation

occurs, and the presence of
Brownian motion
.

There are three main types of dispersions: Coarse dispersion
(Suspension); Colloid; Solution.


It is still common belief, that dispersions basically do not display any
structure, i.e., the particles (or in case of emulsions: droplets) dispersed in
the liquid or solid matrix (the "dispersion medium") are assumed to be
statistically distributed. Therefore, for dispersions usually
percolation
theory

is assumed to appropriately describe their properties.

However, percolation theory can only be applied if the system it should
describe is in or close to
thermodynamic equilibrium
. There are only very
few studies about the structure of dispersions (emulsions), although they
are plentiful in type and in use all over the world in innumerable
applications (see below).

In the following, only such dispersions will be discussed with a dispersed
phase diameter of less than 1

µm. To understand the formation and
properties of such dispersions (incl emulsions), it must be considered, that
the dispersed phase exhibits a "surface", which is covered ("wet") by a
different "surface" which hence are forming an
interface (chemistry)
. Both
surfaces have to be created (which requires a huge amount of energy),
and the interfacial tension (difference of surface tension) is not
compensating the energy input, if at all.


A review article in introduces into various attempts to describe dispersions
/ emulsions. Dispersion is a process by which (in the case of solids
becoming dispersed in a liquid) agglomerated particles are separated
from each other and a new interface, between an inner surface of the
liquid dispersion medium and the surface of the particles to be dispersed,
is generated. Dispersion is a much more complicated (and less well
understood) process than most people believe.


PRESIPITASI = PENGENDAPAN

http://en.wikipedia.org/wiki/Precipitation_%28chemistry%29 ….. Diunduh 28/2/2012

Precipitation

is the formation of a solid in a solution or inside another
solid during a chemical reaction or by diffusion in a solid. When the
reaction occurs in a liquid, the solid formed is called the
Precipitate
,
or when compacted by a centrifuge, a
pellet
. The liquid remaining
above the solid is in either case called the
supernate

or
supernatant
. Powders derived from precipitation have also
historically been known as
flowers
.


Natural methods of precipitate include settling or sedimentation,
where a solid forms over a period of time due to ambient forces like
gravity or centrifugation. During chemical reactions, precipitation may
also occur particularly if an insoluble substance is introduced into a
solution and the density happens to be greater (otherwise the
precipitate would float or form a suspension). With soluble
substances, precipitation is accelerated once the solution becomes
supersaturated.

In solids, precipitation occurs if the concentration of one solid is above
the solubility limit in the host solid, due to e.g. rapid quenching or
ion
implantation
, and the temperature is high enough that diffusion can
lead to segregation into precipitates. Precipitation in solids is routinely
used to synthesize nanoclusters.


An important stage of the precipitation process is the
onset of nucleation. The creation of a hypothetical solid
particle includes the formation of an interface, which
requires some energy based on the relative surface
energy of the solid and the solution. If this energy is not
available, and no suitable nucleation surface is available,
supersaturation occurs.

FLOKULASI

http://en.wikipedia.org/wiki/Flocculation ….. Diunduh 28/2/2012

Flocculation
, in the field of chemistry, is a process wherein
colloids come out of suspension in the form of floc or flakes by
the addition of a clarifying agent.


The action differs from precipitation in that, prior to
flocculation, colloids are merely suspended in a liquid and not
actually dissolved in a solution. In the flocculated system,
there is no formation of a cake, since all the flocs are in the
suspension.


Surface chemistry

In colloid chemistry, flocculation refers to the process by
which fine particulates are caused to clump together into a
floc. The floc may then float to the top of the liquid,
settle

to
the bottom of the liquid, or be readily
filtered

from the liquid.


Physical chemistry

For emulsions, flocculation describes clustering
of individual dispersed droplets together,
whereby the individual droplets do not lose their
identity.

Flocculation is thus the initial step leading to
further aging of the emulsion (droplet
coalescence and the ultimate separation of the
phases).



AGREGASI

….. Diunduh 28/2/2012

Natural sciences and statistics:


1.
Aggregation of soil granules to form
soil structure

2.
Particle aggregation, direct mutual attraction between
particles (atoms or molecules) via van
der

Waals forces or
chemical bonding

3.
The accumulation of platelets to the site of a wound to
form a platelet plug or a thrombus

4.
Flocculation
, a process where a solute comes out of
solution in the form of
floc

or flakes

5.
Overdispersion

or statistical aggregation, where the
variance of a distribution is higher than expected

6.
Aggregation pheromone

7.
Protein aggregation, the aggregation of
mis
-
folded
proteins


Particle aggregation

in materials science is direct mutual
attraction between particles (atoms or molecules) via van
der

Waals forces or chemical bonding.

Particle aggregation is often spontaneous and involves one
particle attaching to another particle or existing aggregate of
particles.

Particle aggregation occurs when particles come into close
contact with each other.

When there are collisions between particles in fluid, there is a
chance that particles will attach to each other and become
larger particle.

There are 3 major physical mechanisms to form aggregate:
Brownian motion, Fluid shear and differential settling.


AGREGATE

….. Diunduh 28/2/2012

An
aggregate

is a collection of items that are gathered together to form a total
quantity.

1.
Aggregate (composite)
, in materials science, a component of a composite
material used to resist compressive stress

2.
Construction aggregate
, materials used in construction, including sand,
gravel, crushed stone, slag, or recycled crushed concrete

3.
In some Christian churches, a group of several
canonical hours

(offices)
combined to form a single religious service

4.
In the social sciences, a gathering of people into a cluster or a crowd that
do not form a true
social group

5.
In music, a set of all twelve pitch classes, also known as the
total chromatic

6.
Aggregate (Sanskrit,
skandha
;
Pāli
,
khandha
), in Buddhism, refers to a
category of sensory experiences

7.
Aggregate analysis, a technique used in
amortized analysis

in computer
science, especially in analysis of algorithms

8.
Aggregate (data warehouse)
, a part of the dimensional model that is used
to speed up query time by summarizing tables

9.
Aggregate data
, in statistics, data combined from several measurements

10.
Aggregate demand
, the total demand for final goods and services during a
specific time period in an economy

11.
Aggregate supply
, the total supply of goods and services produced during a
specific time period in an economy

12.
Aggregate function
, in computer science (especially SQL), a function that
calculates a single result (scalar) from a collection of input values

13.
Aggregate score
, in sport, the sum of two
scorelines

in a two
-
legged match

14.
Aggregate (rocket family)
, in rocketry, a set of experimental rocket designs
developed in Nazi Germany

15.
Aggregate species (
Wiktionary
)

or Species aggregate, a named species
representing a range of very closely related organisms

16.
Aggregate Spend

(US), a process to monitor the total amount spent by
healthcare manufacturers on individual healthcare professionals and
organizations through payments and gifts of various kinds

17.
AggreGate

Platform
, a software framework for managing diverse electronic
devices

Aggregate Root
,
Domain Driven Design

concept

STRUKTUR TANAH:

Na dan Garam
-
garam

Dr. Jim Walworth

Department of Soil, Water and Environmental Science

University of Arizona

AGREGASI

Proses
-
proses dimana partikel tanah utama
(pasir, debu, liat) terikat bersama
-
sama oleh
gaya alami dan bahan
-
bahan yang dihasilkan
oleh eksudat akar dan aktifitas mikrobia.


DISPERSI

(i) Memecah gugusan partikel,
seperti agregat, menjadi gugusan
partikel individual.

(ii) Mendistribusikan atau
mengendapkan partikel
-
partikel
halus, seperti liat, di dalam atau
melalui media dispersi, seperti air.


FLOKULASI


Soil clay particles can be unattached to one another
(
dispersed
) or clumped together (
flocculated
) in
aggregates. Soil aggregates are cemented clusters of
sand, silt, and clay particles.

Dispersed Particles

Flocculated Particles

Struktur tanah dapat berkembang dari penggabungan
partikel primer tanah dengan perekat bahan koloid (koloid liat
dan koloid humus) menjadi agregat mikro.


Penggabungan agregat mikro menjadi agregat makro yang
ukurannya lebih besar.


Dr. Jim Walworth

Department of Soil, Water and
Environmental Science

University of Arizona


FLOKULASI
-

AGREGASI

Flocculation is important because water moves mostly in
large pores between aggregates. Also, plant roots grow
mainly between aggregates.

Soil aggregates are clumps of soil particles that are held together by moist clay,
organic matter (like roots), gums (from bacteria and fungi) and by fungal hyphae.
The aggregates are relatively stable. Aggregates vary in size from about 2
thousandths of a millimetre across, up to about 2 millimetres across. Soil pores are
the spaces between soil particles and between soil aggregates. They can be full of
air or they can have water in them. Soils with lots of aggregates are called "well
-
aggregated" and this condition is thought to be very desirable, for a number of
reasons. The aggregates are made up of particles of different sizes and some of
these particles fit closely together. Some do not. This means that there are spaces
of many different sizes in the soil and these spaces are essential for storing air,
water, microbes, nutrients and organic matter.
http://www.soilhealth.com/biology/formation.htm

Dr. Jim Walworth

Department of Soil, Water and
Environmental Science

University of Arizona


DISPERSI AGREGAT MENJADI KERAK
PERMUKAAN

In all but the sandiest soils, dispersed clays plug soil pores
and impede water infiltration and soil drainage.

The structural stability of soil aggregates upon wetting has been the
subject of a great deal of research around the world. The combination of
slaking and dispersion caused a reduction in macroporosity and,
therefore, lower infiltration rates and hydraulic conductivities as well as
an increase in soil strength and other undesirable soil physical
properties.
http://vro.dpi.vic.gov.au/dpi/vro/vrosite.nsf/pages/soil_mgmt_slaking

Dr. Jim Walworth

Department of Soil, Water
and Environmental Science

University of Arizona


MUATAN NEGATIF DI
PERMUKAAN


Most clay particles have a negative electrical charge.
Like charges repel, so clay particles repel one another.

Negatively
charged clay
particle

Negatively
charged clay
particle

Surface charge

is the electric charge present at an interface. There
are many different processes which can lead to a surface being
charged, including adsorption of ions, protonation/deprotonation, and
the application of an external electric field. Surface charge causes a
particle to emit an electric field, which causes particle repulsions and
attractions, and is responsible for many colloidal properties.


http://en.wikipedia.org/wiki/Surface_charge

Dr. Jim Walworth

Department of Soil, Water
and Environmental Science

University of Arizona

KATION SEBAGAI PEREKAT


A cation is a positively charged molecule. Common soil
cations include sodium (Na
+
), potassium (K
+
), magnesium
(Mg
2+
), and calcium (Ca
2+
).


Cations can make clay particles stick together (flocculate).

Negatively
charged clay
particle

Negatively
charged clay
particle

+

Vermiculite or Smectite
.

The case for low
-
charge 2:1 structures is notably different from 1:1 structures.
The schematic diagram below shows that 2:1 structures have mostly positive
ions are attracted to the light
-
blue tetrahedral basal oxygen surfaces.

Sumber: http://www.gly.uga.edu/Schroeder/geol6550/CM19.html

KATION FLOKULASI


We can divide cations into two categories


Poor flocculators


Sodium


Good flocculators


Calcium


Magnesium




Ion

Relative
Flocculating
Power

Sodium

Na
+

1.0

Potassium

K
+

1.7

Magnesium

Mg
2+

27.0

Calcium

Ca
2+

43.0

Sumber: Sumner and Naidu, 1998

KATION SEBAGAI
PEREKAT FLOKULE

Cations in water attract water molecules because of their
charge, and become hydrated.

Cations with a single charge and large hydrated radii are the
poorest flocculators.

Cation

Charges
per
molecule

Hydrated
radius (nm)

Relative
flocculating
power

Sodium

1

0.79

1.0

Potassium

1

0.53

1.7

Magnesium

2

1.08

27.0

Calcium

2

0.96

43.0

Water molecule
is polar: (+) on
one end, (
-
) on
the other end

(+
)

(
-
)

(+
)

Hydrated
cation

+

SAR = Sodium Adsorption
Ratio

The ratio of ‘bad’ to ‘good’ flocculators gives
an indication of the relative status of
these cations:

+

+

+

+

+

+

+

Ca
2+

and
Mg
2+

++

++

++

++

++

++

++

Mathematically, this is expressed as

the ‘sodium adsorption ratio’ or SAR:










where concentrations are expressed in mmoles/L

SAR =

[Na
+
]

[Ca
2+
] + [Mg
2+
]

Dr. Jim Walworth

Department of Soil, Water
and Environmental Science

University of Arizona

DAYA HANTAR LISTRIK

Ions in solution conduct electricity, so the total amount
of soluble soil ions can be estimated by measuring
the electrical conductivity (EC) of a soil water
extract.




EC is measured in units of conductance over a
known distance:



deci
-
Siemens per meter or dS/m


Soil with a high EC is salty; soil with a low EC is
not.

Electrical conductivity (EC) estimates the amount of
total dissolved salts (TDS), or the total amount of
dissolved ions in the SOIL solution.




Soil electrical conductivity (EC) is a measurement
that correlates with soil properties that affect crop
productivity, including soil texture, cation exchange
capacity (CEC), drainage conditions, organic matter
level, salinity, and subsoil characteristics.


Sumber: http://pubs.ext.vt.edu/442/442
-
508/442
-
508_pdf.pdf

E
C

STABILITAS AGREGAT

Aggregate stability (dispersion and flocculation)
depends on the balance (SAR) between (Ca
2+
and Mg
2+
)
and Na
+

as well as the amount of soluble salts (EC) in
the soil.

Flocculated
soil

Dispersed
soil

++

++

++

++

++

+

+

+

+

+

++

++

+

+

Lower EC

Higher EC

Dr. Jim Walworth

Department of Soil, Water
and Environmental Science

University of Arizona

E
C

KATION PEREKAT FLOKULASI

Soil particles will flocculate if concentrations of (Ca
2+

+
Mg
2+
) are increased relative to the concentration of Na
+
(SAR is decreased).

Flocculated
soil

Dispersed
soil

Dr. Jim Walworth

Department of Soil, Water
and Environmental Science

University of Arizona

E
C

Flocculated soil

Dispersed
soil

Na dan DISPERSI

Soil particles will disperse if concentrations of (Ca
2+

+
Mg
2+
) are decreased relative to the concentration of Na
+

(SAR is increased).

FLOKULASI DAN EC

Soil particles will flocculate if the amount of soluble
salts in the soil is increased (increased EC), even if
there is a lot of sodium.

Flocculated
soil

Dispersed
soil

E
C

Lower EC

Higher EC

DISPERSI

Soil particles may disperse if the amount of soluble
salts in the soil is decreased (i.e. if EC is decreased).

E
C

Lower EC

Flocculated
soil

Dispersed
soil

Higher EC

Soils irrigated with saline water
(with high EC) will generally have
good structure, and water will
infiltrate rapidly. However, salts
can accumulate and damage
plants unless properly managed.

E
C

Lower EC

Dispers
ed soil

Higher EC

Higher EC

Floccula
ted soil

E
C

Lower EC

If soils are irrigated with clean
water (with low EC), soil EC will
decrease, which can destabilize
aggregates. Irrigation water will
infiltrate slowly.

STABILITAS AGREGAT

If soils are close to the “tipping point” between flocculation
and dispersion, the quality of irrigation water will influence
aggregate stability. If irrigation water infiltrates, and rain
water does not, this indicates that the soil is close to the
“tipping point”.

Soil
Classification

EC

SAR

Condition

Normal

<4

<13

Flocculated

Saline

>4

<13

Flocculated

Sodic

<4

>13

Dispersed

Saline
-
Sodic

>4

>13

Flocculated

TANAH SALIN DAN SODIK

Soils can be classified by the amount of soluble salts (EC) and
sodium status (SAR). This classification can tell us something
about soil structure.

EC

KALSIUM DAN STABILITAS AGREGAT

Increasing
soluble

calcium improves aggregate stability in
soils with poor structure.

Flocculated
soil

Dispersed
soil

Gypsum

CaSO
4

GIPSUM UNTUK AGREGASI TANAH


Apply gypsum
before

leaching salts out of soils susceptible
to dispersion (the amount of gypsum needed can be
determined by a soil test). Replacing sodium with calcium
before leaching will stabilize soil structure.

Na
+

Na
+

Na
+

Na
+

Na
+

Na
+

-

-

-

-

-

-

-

-

-

Ca
++

Ca
++

Ca
++

Ca
+
+

Ca
2+

SO
4
2
-

-

-

-

-

-

-

-

-

-

Na
+

Na
+

Na
+

Na
+

Na
+

Na
+

Na
+

Na
+

Na
+

Na
+

Sulfuric acid
*

can be used instead of gypsum on
calcareous (CaCO
3
containing) soil only.


Sulfuric acid

dissolves
calcium
carbonate

in the soil














and makes gypsum!









H
SO
CaCO
CO
H
O
CaSO
2
4
3
2
2
4




*
Sulfuric acid is extremely dangerous and should only
be handled

by trained personnel.

DISPERSI TANAH

Soil dispersion causes clay particles to plug soil pores, resulting
in reduced soil permeability. When soil is repeatedly wetted and
dried and clay dispersion occurs, it then reforms and solidifies into
almost cement
-
like soil with little or no structure.
The three main
problems caused by sodium
-
induced dispersion are reduced
infiltration, reduced hydraulic conductivity, and surface
crusting.

http://waterquality.montana.edu/docs/methane/basics_highlight.shtml….. Diunduh
28/2/2012

Behavior of sodium and calcium attached to a clay particles.
(After Hanson et al., 1999).

FLOKULASI

http://www.ozcoasts.gov.au/glossary/def_e
-
h.jsp….. Diunduh 28/2/2012

Flocculation in coastal waterways is a process in which
particles of clay and organic matter stick together, through
chemical interactions with divalent
calcium and magnesium
ions
, to form larger flake
-
like particles (flocs or floccules) that
may come out of solution. Flocculation influences the
transport of fine
-
grained sediment, and enhances its
deposition rate. Because particles belonging to various size
classes can form flocs, the sediment that is deposited is often
poorly sorted .

FLOKULASI

http://www.terragis.bees.unsw.edu.au/terraGIS_soil/sp_stability_indices.html…..
Diunduh 28/2/2012

Soil structure refers to the way ultimate soil particles (i.e. clay, silt and sand) are
arranged and bound together into groupings called aggregates or peds. The
exchangeable cation of calcium, can initiate aggregation of these particles in a
process called flocculation.

Flocculation occurs because the two positive charges of the calcium ion can
attach to two separate and negatively charged clay mineral particle or organic
colloid surfaces. This is similarly the case for aluminium. These cations
effectively neutralize the negative surface charges.

FLOKULASI
-

AGREGASI

http://www.terragis.bees.unsw.edu.au/terraGIS_soil/sp_stability_indices.html…..
Diunduh 28/2/2012

The process of flocculation alone, however, does not make
aggregates stable. Various soil satabilising agents are also
necessary for the particles to aggregate.

This includes the presence of clay minerals, sesquioxides (i.e.
aluminium
-

and iron
-
oxides) and humus. In the first instance,
the negatively charged clay mineral surfaces can interact with
each other and with sand and silt sized particles to form
aggregates.

In addition, oxides of iron also link particles because some
having positive charges, while other oxides have no charge
but can build up tough coatings that connect particles.

Finally, large organic molecules tend to form bridges between
mineral particles, either with electrostatic charge or by linking
particles together like a net. Soil microorganisms provide the
best cement because as they break down soil residues they
produce gums that glue peds together.

These stabilizing agents along with the processes of localised
compression resulting from repeated cycles of

soil wetting
and drying, shrinking and swelling and the action of
organisms (flora and fauna) result in the repeated
compression of the same soil mass. This leads to the
increased coherence of aggregates (peds) that are difficult to
pull apart.

The result is a well aggregated soil which contains large
cracks or voids between the aggregated soil particles. These
larger voids or macropores improve water infiltration, gaseous
exchange and root penetration.

KOAGOLASI atau FLOKULASI

http://chemistry.tutorvista.com/physical
-
chemistry/flocculation.html ….. Diunduh 28/2/2012

Coagulation is the process by which a colloid precipitates out of a solution. The
precipitation is brought about by induced aggregation. For e.g., an iron (III)
hydroxide sol can be made to aggregate by addition of an ionic solution. A
positively charged particle of iron (III) hydroxide gathers a layer of anions
around it. The thickness of this layer is determined by the charge on the anions.
The greater the magnitude of the negative charge, the more compact the layer
of charge. For e.g., phosphate ions gather more closely to the positively charge
iron (III) particle than do chloride ions.


Layers of ions surrounding a charged particle of iron (III) hydroxide.A: Fe(OH)
3

surrounded by Cl
-

ionsB: Fe(OH)
3

surrounded by PO
4
3
-

ions

If the ion layer is gathered close to the colloidal particles, the overall charge is
effectively neutralized and two colloidal particles can approach close enough to
aggregate and precipitate out.

The coagulation of colloids by an electrolyte takes place only when the electrolyte
has a certain minimum concentration.

The minimum concentration of electrolyte in millimoles that is added to one liter of
the colloidal sol to bring about complete coagulation is called the flocculation
value of the electrolyte for the sol.

Different electrolytes have different coagulation values. Smaller the coagulation
value of the electrolyte, larger is its coagulating power. According to Hardy and
Schulze, coagulation of colloids by electrolytes is governed by two factors, namely

i) Ions carrying charge opposite to that of the colloidal particles are effective in
bringing about coagulation.

ii) Coagulation power of an electrolyte is directly proportional to the valency of its
ions.

Coagulation Values of Electrolytes

http://chemistry.tutorvista.com/physical
-
chemistry/flocculation.html ….. Diunduh
28/2/2012

Coagulation of Negatively Charged Colloids As2s3

Coagulation Positively Charged Colloids Fe(oh)3

Elemental sulfur can also be
used as an alternative to
gypsum on calcareous soils


Soil microbes convert sulfur into sulfuric acid





H
2
SO
4

dissolves calcium carbonate and
makes gypsum


Conversion to sulfuric acid takes time


several weeks


faster in warm soils


S
O
CO
H
O
H
SO
CH
O





½
2
2
2
2
4
2
2
PENGELOLAAN STRUKTUR TANAH


Be aware of the quality of irrigation water. Water
with high levels of sodium (high SAR) will tend to
destabilize soil.


Have irrigation water analyzed for SAR and EC or
ask your water provider for analyses.


If you have high sodium irrigation water, the water
and/or the soil may need amendments such as
gypsum or sulfuric acid.



Observe your soil.


If water infiltrates very slowly, or if rain water
infiltrates more slowly than irrigation water, the soil
may have a sodium problem.


Sodium impacted soils may noticeably crack when
dry.



Analyze your soil.


Laboratory analysis can tell you the soil EC and
SAR or ESP.

STRUKTUR TANAH

http://en.wikipedia.org/wiki/Soil_structure ….. Diunduh 28/2/2012

Soil structure describes the arrangement of the solid parts of the soil
and of the pore space located between them (Marshall & Holmes,
1979). The structure depends on what the soil developed from. The
practices that influence soil structure will decline under most forms of
cultivation

the associated mechanical mixing of the soil compacts
and shears aggregates and fills pore spaces; it also exposes organic
matter to a greater rate of decay and oxidation (Young & Young,
2001). A further consequence of continued cultivation and traffic is the
development of compacted, impermeable layers or pans within the
profile.

Soil structure decline under irrigation is usually related to the
breakdown of aggregates and dispersion of clay material as a result
of rapid wetting. This is particularly so if soils are sodic; that is, having
a high exchangeable sodium percentage (ESP) of the cations
attached to the clays. High sodium levels (compared to high calcium
levels) cause particles to repel one another when wet and for the
associated aggregates to disaggregate and disperse. The ESP will
increase if irrigation causes salty water (even of low concentration) to
gain access to the soil.

A wide range of practices are undertaken to preserve and improve
soil structure. For example, the NSW Department of Land and Water
Conservation, (1991) advocates: increasing organic content by
incorporating pasture phases into cropping rotations; reducing or
eliminating tillage and cultivation in cropping and pasture activities;
avoiding soil disturbance during periods of excessive dry or wet when
soils may accordingly tend to shatter or smear, and; ensuring
sufficient ground cover to protect the soil from raindrop impact. In
irrigated agriculture, it may be recommended to: apply gypsum
(
calcium sulfate
) to displace sodium cations with calcium and so
reduce ESP or
sodicity
; avoid rapid wetting, and; avoid disturbing
soils when too wet or dry.

MANFAAT PERBAIKAN STRUKTUR TANAH

http://en.wikipedia.org/wiki/Soil_structure ….. Diunduh 28/2/2012


The benefits of improving soil structure for the growth of
plants, particularly in an agricultural setting include:

1.
reduced erosion due to greater soil aggregate strength
and decreased overland flow;

2.
improved root penetration and access to soil moisture and
nutrients;

3.
improved emergence of seedlings due to reduced crusting
of the surface and;

4.
greater water infiltration, retention and availability due to
improved porosity.


It has been estimated that productivity from irrigated perennial
horticulture could be increased by two to three times the
present level by improving soil structure, because of the
resulting access by plants to available soil water and nutrients
(
Cockroft

& Olsson, 2000, cited in Land and Water Australia
2007).

The NSW Department of Land and Water Conservation
(1991) infers that in cropping systems, for every
millimetre

of
rain that is able to infiltrate, as
maximised

by good soil
structure, wheat yields can be increased by 10

kg/ha.


GRANULE

http://en.wikipedia.org/wiki/Granules ….. Diunduh 28/2/2012

Granule

is a generic term used for a small particle or grain.
The generic term is employed in a variety of specific contexts.


1.
Granule (solar physics)
, visible structures in the
photosphere of the Sun arising from activity in the Sun's
convective zone


2.
Granule (cell biology)
, any of several submicroscopic
structures, some with explicable origins, others noted only
as cell type
-
specific features of unknown function

3.
"
Azurophil

granule", a structure characteristic of the
azurophil

eukarytotic

cell type


4.
"
Chromaffin

granule", a structure characteristic of the
chromophil

eukaryotic cell type

5.
Martian spherules
, spherical granules of material found on
the surface of the planet Mars


6.
Granule (geology)
, a specified particle size of 2

4
millimetres

(
-
1

-
2 on the
φ
scale)


7.
In pharmaceutical terms, a granule is small particles
gathered into a larger, permanent aggregate in which the
original particles can still be identified


8.
In the
Oracle database
, a unit of contiguously allocated
virtual memory

FLOKULASI


AGREGASI

On their own, these units are pretty fragile and the process
is easily reversed. But in the presence of natural or artificial
binding

become more strongly cemented together forming
stable soil aggregates.

These binding agents may be:


Inorganic


Fe & Al oxides, carbonates,

amorphous gels and sols; or


Organic


polysaccharides, hemicellulose, and

other natural or manufactured organic

polymers.


Changes in a) water
-
stable macroaggregation and b) organic
carbon content under alfalfa, corn and fallow soil in a Humic Gleysol
(modified from Angers and Carter, 1996).



http://grdc.com.au/director/events/grdcpublications.cfm?item_id=2E7B554DF796461
47F64C3704857B3EF&article_id=2EB7FE10AB38F7F2E7741544C2737396 …..
Diunduh 10/3/2012

….. Diunduh 28/2/2012

The arrangement or organization of individual soil particles (soil
separates) into a specific configuration is called “
soil structure
”.

Soil structure is developed over a geologic time frame, is (or can
be) naturally fragile, and is affected by changes in climate,
vegetation, biological activity, and anthropogenic manipulation.

Soil structure influences the mechanical properties of soil such as
stability, porosity and compaction, as well as plant growth,
hydrologic function, and erosion.


Influence of organic amendments on soil aggregate stability. Arrows
indicate addition of organic amendments (modified from Martens and
Frankenberger, 1992).

http://grdc.com.au/director/events/grdcpublications.cfm?item_id=2E7B554DF796461
47F64C3704857B3EF&article_id=2EB7FE10AB38F7F2E7741544C2737396 …..
Diunduh 10/3/2012

TATANAN SEPARATE TANAH

There are three broad categories of soil structure;
single grained, massive, and aggregated.


When particles are entirely unattached the structure is completely
loose and such soils are labeled single grained. When packed into
large cohesive blocks the structure is called massive.

Neither have any visible structural characteristics.

Between these two extremes particles are present as aggregates or
peds.



Relationship between aggregate stability and organic matter content
for 26 soils (redrawn from Chaney and Swift, 1984).

http://grdc.com.au/director/events/grdcpublications.cfm?item_id=2E7B554DF796461
47F64C3704857B3EF&article_id=2EB7FE10AB38F7F2E7741544C2737396 …..
Diunduh 10/3/2012

BENTUK
-
BENTUK STRUKTUR
TANAH

Platy:

Horizontally layered, thin, flat
aggregates similar to wafers.


Spherical
:

Rounded aggregates
generally < 2.0 cm in diameter that are
often found in loose condition called
“granules or crumbs”.


Blocky
:

Cube
-
like blocks, sometimes
angular with well
-
defined sharp faces or
sub
-
angular with rounded faces up to
10cm in size.


Columnar or Prismatic
:

Vertically
oriented pillars up to 15cm in diameter.

….. Diunduh 28/2/2012

http://www.landfood.ubc.ca/soil200/interaction/structure.htm ….. Diunduh 28/2/2012

AGREGASI = Formation of Aggregates

aggregation = flocculation + cementation


Flocculation is the first step in aggregate formation.


flocculation:
when
primary particles remain
close together due to
interactive forces
(electrostatic, van
der

Waals, and/or hydrogen
bonding) and form
microscopic floccules

cementation:
stabilization
of floccules by action of a
cementing agent such
(organic compounds,
carbonates, Fe and Al
oxides, clays)

Aggregate Formation: Illustration of several levels in
aggregate formation


http://www.landfood.ubc.ca/soil200/interaction/structure.htm ….. Diunduh 28/2/2012




PENGELOLAAN STRUKTUR TANAH

http://vro.dpi.vic.gov.au/dpi/vro/vrosite.nsf/pages/soilhealth_changing_soil_structure
….. Diunduh 28/2/2012

Humans have considerable potential to change soil structure.
The range of management actions that can change (both
positively and negatively) soil structure include:


Vegetation management


Clearing

Stubble retention

Fallow phases

Pasture development

Crop rotations

Ley phases

Plantations


Trafficking
Stock treading

Vehicle movement


Controlled traffic


Tillage

Cultivation practices


Re
-
forming soils

Laser levelling

Raised beds

Contour banks and terracing

Gypsum for responsive soils


Subsoil management

Controlled traffic

Deeper tillage

Primer crops (e.g. lucerne, chicory)

Drainage

Ameliorants (e.g. worms, gypsum)

PENTINGNYA STRUKTUR TANAH

http://vro.dpi.vic.gov.au/dpi/vro/vrosite.nsf/pages/soilhealth_soil_structure …..
Diunduh 28/2/2012


Soil is like a city


The structure and layout of both determine how things
happen, the rate at which they happen, and the
capability to keep them happening.

The following characteristics are used to help evaluate
the ability of any soil to perform well (or otherwise):


1.
Porosity

(to represent aeration, water storage
capacity, plant wilting point and drainage)

2.
Permeability (to represent infiltration, drainage and
respiration)

3.
Bonding and aggregation

(to represent how the
solids group together and the construction materials
used)

4.
Soil strength

(to represent toughness and resilience
of structures)

5.
Friability,
tillage

and
trafficability

(to represent how
soils behave with mechanical disturbance)


AGREGATE TANAH

http://saret.ifas.ufl.edu/publications/bsbc/chap6.htm ….. Diunduh 28/2/2012

A well aggregated soil has a range of pore sizes. This medium
size soil crumb is made up of many smaller ones. Very large
pores occur between the medium size aggregates.

http://tedspeds.wordpress.com/raindrops/ ….. Diunduh 28/2/2012

AGREGASI PARTIKEL TANAH


Clay particles have a plate like shape. Domains are a number of
clay particles stacked up together. The surfaces of clay particles
are negatively charged and the electrostatic forces can form
either attraction or repulsion forces between clay particles.
Calcium ions


increase attraction forces and the flocculation of
clay particles. Sodium ions increase repulsion forces and the
dispersion of clay particles.

Organic colloids can cement soil particles together. Iron and
aluminum hydroxides also are cementing agents.

Fungi and actinomycetes hypha bind soil particles together. Plant
roots help to form a stable structure.

Bacteria are surrounded by a sticky gel binding soil particles
together.

Platy and spherical soil structure is common to the
surface soil horizons, blocky and columnar/prismatic
are associated with the deeper subsurface soil
horizons


Non
-
Structured


Single Grain





















Massive


Structured



Platy: horizontal &
flat



Spherical
(Grannular):
rounded and <2.0
cm



Blocky: cubes up to
10 cm that are
angular (sharp
edges) or
subangular
(rounded)



Prismatic
(Columnar): longer
than wide, often 6
sided, sharp or
rounded, < 15 cm

….. Diunduh 28/2/2012

Aggregate size distribution also influences the
pore size distribution.


Macropores: Inter
-
aggregate cavities that
influence infiltration, drainage, and aeration.


Micropores: Intra
-
aggregate capillaries
important to water and solute retention.


Mesopore: In between.

AGREGASI DAN PORI TANAH

http://ridge.icu.ac.jp/biobk/BioBookPLANTHORM.html….. Diunduh 28/2/2012

DISTRIBUSI UKURAN AGREGAT

Similar to particle size distribution, the aggregate size
distribution also is determined by sieving.

An index known as the Mean Weight Diameter (X)
based on the size and weight distribution of
aggregates is derived by weighing the mass of
aggregates within the respective size classes, and
characterizing the overall size distribution.

(MWD) X =
∑ x
i
w
i


x
i
= mean diameter w
i

= dry mass fraction

http://www.consumer.org.nz/reports/soil
-
quality/check
-
your
-
soil
-
condition….. Diunduh
28/2/2012

Since aggregation and stability is time dependent,
another useful characterization is that of “
aggregate
stability
”.

Aggregate stability expresses
the resistance of individual
soil aggregates to disruptive
forces such as mechanical,
wind, and water erosion;
freezing/thawing;
wetting/drying; and air
entrapment.

The level of stability is
assessed by determining the
fraction of the original
aggregate mass which has
withstood disruptive forces.
The laboratory approach uses
wetting (misting and/or from
bottom up with de
-
aired water)
followed by sieving.

STABILITAS AGREGAT

http://www.consumer.org.nz/reports/soil
-
quality/check
-
your
-
soil
-
condition….. Diunduh
28/2/2012

The consequences of aggregate destruction are
manifest in soil crusting, surface seal, dust
generation, etc.

Aggregate stability can be enhanced through the
use of synthetic polymers, but they are typically
quite expensive.

STABILITAS AGREGAT

http://ipmguidelines.org/FieldCrops/Chapters/CH02/CH02
-
5.aspx ….. Diunduh
10/3/2012

Relationship between aggregate stability and soil organic
matter in some selected soils from the Cornell University
research sites in NY.

The higher the soil organic matter in mineral soils, the higher the
soil aggregate stability.

IMPORTANT INHERENT SOIL
PROPERTIES

Soil structure and aggregate stability


Soil structural stability refers to the resistance of soil to structural
rearrangement of pores and particles when exposed to different
stresses (e.g. cultivation, trampling/compaction, and irrigation).

It is well established that addition of SOM can not only reduce bulk
density (
D
b
) and increase water holding capacity, but also effectively
increase soil aggregate stability.

Effect of increasing SOC content on aggregate stability, measured by
wet
-
sieving (MWD, mm), using air
-
dried () and field moist () samples
(R = 0.98***) (modified after Haynes, 2000).

http://grdc.com.au/director/events/grdcpublications.cfm?item_id=2E7B554DF796461
47F64C3704857B3EF&article_id=2EB7FE10AB38F7F2E7741544C2737396 …..
Diunduh 28/2/2012

PROFIL TANAH

http://www.grovida.com/horticulture
-
guide/soil
-
structure.html ….. Diunduh 28/2/2012

The soil profile on the left
is composed of soil
particles aggregated into
structures that produce
good growing conditions.
Examples of structures
that create a poor rooting
environment are shown
in the profile on the right.

….. Diunduh 28/2/2012

SEGITIGA TEKSTUR TANAH

….. Diunduh 28/2/2012

BENTUK ATAU TIPE STRUKTUR TANAH

PENGELOLAAN STRUKTUR TANAH

http://www.omafra.gov.on.ca/english/environment/soil/structure.htm ….. Diunduh
28/2/2012

If your soil has structural problems, chances are it is weather
-
sensitive or
stress
-
prone due to difficulties in root development and soil exploitation. Well
-
managed soils are productive, even under difficult growing conditions.

To maintain yields, short
-
term solutions are often used (such as extra fertilizer,
better hybrids, and irrigation), even though poor soil structure is the main
problem.

There are four main types of soil structure problems that occur across a range
of soil types in Ontario:

crusting

compaction

under
-
consolidation

setting
-
up.


Soils farmed with modern agriculture rarely appear like the ideal soil. The
processes of tilage, crop seeding, and harvesting tend to destroy aggregates
and create a platy or compacted layer. Note how the bulk density increases in
the compacted areas, and the impact on crop rooting.

PEMBENTUKAN KERAK TANAH


http://www.omafra.gov.on.ca/english/environment/soil/structure.htm ….. Diunduh
28/2/2012

Following the rapid wetting and drying of an overworked
seedbed, a solid sheet forms (0.2 to 5
centimetres

thick) that
is tight enough to prevent crop emergence. This is known as
soil crusting.


Field Symptoms

following an intensive rain, the soil in top 1 to 2
centimetres

flows together to form one solid sheet

water ponds on the surface

soil structure below crust still intact.


Best Management Practices

1.
reduce secondary tillage; don't overwork the soil

2.
use reduced tillage, no
-
till, or ridge tillage systems to leave
crop residue on the soil surface

3.
use a good crop rotation
-

include grasses and legumes
where possible

4.
use cover crops

5.
use manure management to build soil organic matter

6.
use timely tillage: work ground at suitable moisture level
to prevent bringing up clods
-

more clods require more
tillage

7.
if a crust has formed before the crop emerges, rotary hoe
to break up the crust
-

this will help the crop emerge,
although this perpetuates soil structural problems

8.
check plant populations: replant as a last resort

9.
a light rain will help soften the crust.


PEMADATAN TANAH

Compaction is the process of increasing soil density by packing
soil particles closer together. It can occur anywhere in the soil
profile, but tends to be seen near the surface or at plow depth.
Good management can lessen the impact of compaction on soil
structure.

Field Symptoms

water is ponding on soil surface

erosion is occurring

pond sizes are getting larger.


Crop Symptoms

crop growth can be slow, stunted, and variable, particularly under stressful
weather conditions

root tips are flattened and/or swollen

roots below compacted layer grow normally

root growth is concentrated along face of soil clods

crop may exhibit various nutrient deficiencies

roots tend to grow sideways or down large
-

sized holes/cracks

roots aren't penetrating evenly into the soil.


Best Management Practices

timely tillage and field operations
-

stay off wet fields; soil should be at
proper moisture conditions at tillage depth

good drainage
-

tile drainage should be installed in fields with variable
drainage

longer crop rotations that include forages/cereals

forage crops
-

leave in for longer than 1 year

tillage equipment
-

ensure it lifts and shatters soil (coulter chisel,
cultivator) as opposed to pulverizing and grinding (disk)

alternate tillage depth so that tillage pans aren't created

limit the amount of traffic, including tillage, across a field

restrict compaction
-

create a long, narrow "footprint" with tire
arrangement, e.g. radials, large tires, tracks limit axle loads to less than 5
tonnes/axle.

http://www.omafra.gov.on.ca/english/environment/soil/structure.htm ….. Diunduh
28/2/2012

STRUKTUR TANAH

http://www.fao.org/docrep/R4082E/r4082e03.htm ….. Diunduh 28/2/2012


Soil structure refers to the
grouping of soil particles (sand,
silt, clay, organic matter and
fertilizers) into porous
compounds. These are called
aggregates. Soil structure also
refers to the arrangement of
these aggregates separated by
pores and cracks.


AGREGAT TANAH

http://www.ctahr.hawaii.edu/mauisoil/a_factor_ts.aspx ….. Diunduh 28/2/2012

Soil Aggregates

Generally, only the very small particles form
aggregates, which includes silicate clays, volcanic ash
minerals, organic matter, and oxides. There are various
mechanisms of soil aggregation.


Mechanisms of soil aggregation


Soil microorganisms excrete substances that act as
cementing agents and bind soil particles together.

Fungi have filaments, called hyphae, which extend into
the soil and tie soil particles together.

Roots also excrete sugars into the soil that help bind
minerals.

Oxides also act as glue and join particles together. This
aggregation process is very common to many highly
weathered tropical soils and is especially prevalent in
Hawaii.

Finally, soil particles may naturally be attracted one
another through electrostatic forces, much like the
attraction between hair and a balloon.

STABILITAS AGREGAT


Stable soil aggregation is a very valuable property of
productive soils. Yet, the stability of soil aggregation is very
reliant on the type of minerals present in the soil. Certain clay
minerals form very stable aggregates, while other clay
minerals form weak aggregates that fall apart very easily.


Highly weathered silicate clays, oxides, and amorphous
volcanic materials tend to form the most stable aggregates.
The presence of organic matter with these materials improves
stable aggregate formation. In nutrient management, the
aggregate stability is important because well
-
aggregated
minerals are well drained and quite workable.


In contrast, less weathered silicate
clays, such as montmorillonite, form
weak aggregates. Some silicate
clays are said to have a shrink
-
swell potential. This means that the
soil minerals expand, or swell,
when wet, causing the soil to
become sticky and drain poorly.
When dry, these soils shrink and
form cracks. The make
-
up of the
lattice structure of silicate clays
determines the shrink
-
swell
potential.

http://www.ctahr.hawaii.edu/mauisoil/a_factor_ts.aspx ….. Diunduh 28/2/2012

PEMBENTUKAN AGREGAT TANAH

http://www.soilandhealth.org/01aglibrary/010117attrasoilmanual/010117attra.html…..
Diunduh 28/2/2012

Microbial byproducts glue soil particles into water
-
stable
aggregates.

Aggregates form in soils when individual soil particles are
oriented and brought together through wetting and drying,
freezing and thawing, and by plant growth and earthworm
activity. The weak electrical forces from calcium and magnesium
hold the soil particles together when the soil dries. When the
aggregates become wet again, however, their stability is
challenged and they may break apart once again. In the case of
earthworm
-
created aggregates, they are stable once they come
out of the worm. An aggregate formed by physical forces
becomes stabilized (will remain intact when wet) through
microbial processes involving organic matter decomposition and
its by
-
products

chiefly gums, waxes, and other glue
-
like
substances. These by
-
products cement the soil particles together
forming water
-
stable aggregates. The aggregate is then strong
enough to hold together when wet

hence the name "water
-
stable."

DEGRADASI AGREGAT TANAH

http://www.soilandhealth.org/01aglibrary/010117attrasoilmanual/010117attra.html…..
Diunduh 28/2/2012

Some factors which destroy or degrade soil aggregates
are:


1.
excessive tillage

2.
working the soil when it is too wet or too dry

3.
use of anhydrous ammonia that speed
decomposition of organic matter

4.
excess nitrogen fertilization

5.
allowing build up of excess sodium from salty
irrigation water or sodium
-
containing fertilizers.


Changes in percentage of
macroaggregates

and accumulation of
whole
-
soil organic C with time since cultivation (modified from
Jastrow
, 1996).

AGREGASI PARTIKEL TANAH

http://www.cnr.uidaho.edu/range456/readings/Heitschmidt_Stuth_Book/Chapter_6/C
hapter6.htm….. Diunduh 28/2/2012

Aggregation occurs when soil particles are mechanically bound by roots,
fungal hyphae, and/or adhesive byproducts of organic matter decay and
microbial syntheses. These mechanically bound particles are then
cemented together by resistent humus components which form chemical
bonds.

The
porosity

(pore volume) of the soil is a function of soil texture and the
degree to which the soil is aggregated. Porosity and pore size
determines the rate of movement of water into soil. Large macropores
which aid high infiltration rates increase with improved aggregation.

The formation of soil aggregates is aided by any action that mixes the
soil thus promoting contact between decomposing organic matter and
inorganic soil particles. This action can be accomplished by wetting and
drying, freezing and thawing, the physical activity of roots and burrowing
animals, and soil churning by hooves or farm implements.


STABILITAS AGREGAT

….. Diunduh 28/2/2012

Aggregation alone is not a guarantee of high infiltration rate.
The other key factor that must be considered is the stability of
the aggregates.


Aggregate stability

is the collective measure of the degree to
which soil particles are bound together and the stability of
those bonds when wetted. Aggregate stability is used as an
index of soil structure and as an empirical definition of
aggregation .



The aggregates creating the soil pore structure must maintain
their structural integrity when wet if infiltration through those
pores is to occur. If the aggregate bonds are upstable when
wetted, the clay particles disperse so the aggregate cluster
begins to break into smaller pieces (slaking). These particles
are then carried by the water and lodge in the remaining
pores, making them smaller or sealing them completely.


This is one way in which soil crusts are formed. A "washed in"
layer where clay particles have clogged soil pores to form a
crust may reduce infiltration rate by as much as 90% (Boyle et
al. 1989).


EFEK VEGETASI TERHADAP

STABILITAS AGREGAT

….. Diunduh 28/2/2012


The herbivorous nature of grazing animals clearly results in
the removal of a portion of the vegetation.


Removal of vegetation
a&cts

aggregate stability in several
ways:


1.
A decrease in cover reduces interception. Consequently,
less kinetic energy is dissipated prior to striking the soil
with the consequence that greater force per storm is
applied to the soil tending to break aggregate bonds.


2.
A decrease in above
-
ground biomass (standing crop and
litter) results in less organic matter eventually being
incorporated into the soil. As previously
dis
-

cussed,
organic matter is an important factor in aggregate
formation and stability.


3.
A decrease in above
-
ground biomass is eventually
mirrored by a decrease in root biomass. Grass roots
create a network physically binding soil particles together.
Furthermore, grass roots induce aggregate formation by
exuding biochemical byproducts which bind soil particles
and distribute organic matter throughout the soil profile.


Graphical presentation of model by Ketterings et al. (1997),
representing the relationship between percentage total carbon in dry
sieved aggregates, percentage total clay of bulk soil, and water
stability of 4
-
10 mm aggregates. The model explained 67% of the
total variability in water
-

stability of aggregates of this size class
(redrawn from Ketterings et al., 1997).

http://grdc.com.au/director/events/grdcpublications.cfm?item_id=2E7B554DF796461
47F64C3704857B3EF&article_id=2EB7FE10AB38F7F2E7741544C2737396

Effect of soil organic matter on soil properties

Organic matter affects both the chemical and physical properties
of the soil and its overall health. Properties influenced by organic
matter include: soil structure; moisture holding capacity; diversity
and activity of soil organisms, both those that are beneficial and
harmful to crop production; and nutrient availability. It also
influences the effects of chemical amendments, fertilizers,
pesticides and herbicides. This chapter focuses on those
properties related to soil moisture and water quality, while
Chapter 6 focuses on those related to sustainable food
production.

http://www.fao.org/docrep/009/a0100e/a0100e08.htm….. Diunduh 29/2/2012


http://www.noble.org/ag/soils/organicmatter/ ….. Diunduh 29/2/2012

What Are the Benefits of Organic Matter?

Nutrient Supply

Organic matter is a reservoir of nutrients that can be released
to the soil. Each percent of organic matter in the soil releases
20 to 30 pounds of nitrogen, 4.5 to 6.6 pounds of P
2
O
5
, and 2
to 3 pounds of sulfur per year. The nutrient release occurs
predominantly in the spring and summer, so summer crops
benefit more from organic
-
matter mineralization than winter
crops.




Water
-
Holding Capacity

Organic matter behaves somewhat like a sponge, with the
ability to absorb and hold up to 90 percent of its weight in
water. A great advantage of the water
-
holding capacity of
organic matter is that the matter will release most of the water
that it absorbs to plants. In contrast, clay holds great
quantities of water, but much of it is unavailable to plants.




Soil Structure Aggregation

Organic matter causes soil to clump and form soil aggregates,
which improves soil structure. With better soil structure,
permeability (infiltration of water through the soil) improves, in
turn improving the soil's ability to take up and hold water.




Erosion Prevention

This property of organic matter is not widely known. Data
used in the universal soil loss equation indicate that
increasing soil organic matter from 1 to 3 percent can reduce
erosion 20 to 33 percent because of increased water
infiltration and stable soil aggregate formation caused by
organic matter.

Organic matter and structure relation

http://users.ictp.it/~pub_off/lectures/lns018/10Bricchi2.pdf ….. Diunduh 29/2/2012


Relation between
OC and 2
-
4 mm
aggregates % for
the two
topographic
positions.


Importance of Soil Bulk Density

http://www.soilsurvey.org/tutorial/page10.asp….. Diunduh 29/2/2012

An ideal soil can be described as being 50% solids and 50% pore
space, with half the pore space filled with air and half with water. This
"ideal" soil would hold sufficient air and water to meet the needs of
plants with enough pore space for easy root penetration, while the
mineral soil particles would provide physical support and plant
essential nutrients. Texture, structure and organic matter combine to
influence the amount of pore space, as shown in the graphic below.

Most soil bulk densities fall between 1.0 g/cm
3

and 2.0 g/cm
3
; root
penetration is severely impacted at bulk densities greater than 1.6 g/cm
3
.
As density increases, pore space decreases and the amount of air and
water held in the soil also decreases. As you can see from the figure
above, soils with granular structure (high percent organic matter) are
higher in percent pore space regardless of the amount of sand or clay in
the soil. Angular blocky structure has about the same percent pore space
irrespective of sand or clay content. Platy structure, usually associated
with compacted soils with low organic matter, has little pore space in
sandy textured soils. Clayey soils with platy structure have little to no pore
space.


STRUKTUR TANAH

http://www.soilsurvey.org/tutorial/page9.asp#e….. Diunduh 29/2/2012

Soil structure is the second most influential
characteristic, after texture, in determining the
behavior or any given soil.


Soils with similar characteristics (vegetation,
climate, texture, and depth) but different structure
will react differently under similar conditions.
Structure influences water infiltration, building site
development and growth of plants. When combined
with soil texture, structure influences the
distribution of soil solids and pore space (called the
soil bulk density).


Soil structure is defined as the grouping or
arrangement of primary particles (sand, silt, clay
and organic matter) into larger, secondary particles
called aggregates or peds. These aggregates can
be described in terms of shape, size, and grade
(distinctness), as you will learn a little later.


In this section the physical, chemical and biological
factors which influence the formation of soil
structure are discussed. The different shapes or
types of structure are presented, and you will
discover how those shapes can affect air and water
movement. The effects (both positive and negative)
of certain human activities on soil structure are
considered.


PENTINGNYA STRUKTUR TANAH

Structure is important in that it can modify
the influence of soil texture. For example, a
(structureless) soil high in clay will have
very fine pores because of the higher
packing ratio of small particles.


Without the ameliorating influence of soil
structure, air, water and plant roots would
move through the soil with great difficulty.
Structure provides larger spaces between
aggregates to facilitate movement.


Air, water and plant roots can penetrate
deeper in the soil; this can be important to
plant survival during times of drought.


The larger voids serve as short
-
term
storage space for water, easily accessed
by plants.


http://www.soilsurvey.org/tutorial/page9.asp#e….. Diunduh 29/2/2012

PEMBENTUKAN

STRUKTUR TANAH


Pembentukan struktur tanah melibatkan
proses
-
proses biologis dan proses
-
proses
fisika
-
kimia.


Physical
-
chemical processes are important
in flocculation (or "bringing together") of
soil particles into aggregates, and in
swelling and shrinking of clay masses.



Proses
-
proses biologis membantu
stabilisasi agregat tanah melalui aksi
-
aksi
fisik binatang yang membuat liang dalam
tanah, akar tumbuhan yang mampu
mengikat agregat, dan produksi perekat
-
organik oleh mikro
-
organisme tanah.


http://www.soilsurvey.org/tutorial/page9.asp#e….. Diunduh 29/2/2012

Physical
-
Chemical Processes

Positively charged ions such as calcium (Ca
2+
), magnesium (Mg
2+
)
and aluminum (Al
3+
), (which are known as
polyvalent cations

because they have more than one positive charge), are key in
initiating the formation of soil structure. Aggregation begins with
flocculation of clay particles (platelets) into microscopic clumps called
floccules
; the cations that are caught between two platelets attract the
negative charges on both platelets, binding them together. Look at the
mineral
smectite

and find the polyvalent cations in the structure. Note
that sodium (Na
+
) is not polyvalent, but monovalent (one positive
charge); its effect is quite different and will be discussed below.