STRUKTUR TANAH
DAN
AGREGASI
(Soemarno, Maret 2012)
Mengapa jalan aspal
ini retak-retak?
FOTO: smno.kampus.ub.jan2013
STRUKTUR TANAH
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.
Sumber: http://www.soils.wisc.edu/courses/SS325/morphology.htm#structure …..
Diunduh 10/3/2012
GRADE STRUKTUR TANAH
Classification of
soil structure
considering
grade, size, and
form of particles.
Abbreviat
ion
Description
Structureless
0
No observable aggregation or no
orderly arrangement of natural
lines of weakness
Weak
1
Poorly formed indistinct peds
Grade
Moderate
2
Strong
3
Well-formed distinct peds,
moderately durable and evident,
but not distinct in undisturbed soil
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
Granular
gr
Crumb
cr
Platy
pl
Blocky
bk
Angular blocky
abk
Subangular
blocky
sbk
Prismatic
pr
Columnar
cpr
Single grain
sg
Massive
m
Description
Relatively nonporous, spheroidal peds, not fitted
to adjoining peds
Relatively porous, spheroidal peds, not fitted to
adjoining peds
Peds are plate-like. The particles are arranged
about a horizontal plane with limited vertical
development. Plates often overlap and impair
permeability
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
Block-like peds bounded by other peds whose
sharp angular faces form the cast for the ped
Block-like peds bounded by other peds whose
rounded subangular faces form the cast for the
ped
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
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
Particles show little or no tendency to adhere to
other particles. Often associated with very
coarse particles
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
Granular
Prismatic
and
and
and
subangula
Platy
crumb
columnar
r blocky
structure
structure
structure
structure
[mm] width
[mm]
[mm]
[mm]
diameter
diameter
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
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
Sumber:
….. Dunduh
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.
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: 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
Very sticky
wvs
Nonplastic
wpo
Soil material adheres to both fingers
Soil material strongly adheres to both
fingers
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
wp
Long wires (>1cm) can be formed and
moderate pressure is needed to deform a
block of the molded material
Plastic
Moist
Dry
Cementati
on
Very plastic
wvp
Loose
ml
Very friable
mvfr
Friable
mfr
Firm
mfi
Very firm
mvfi
Extremely firm
mefi
Loose
Soft
Slightly hard
Hard
Very hard
Extremely hard
dl
ds
dsh
dh
dvh
deh
Weakly cemented
cw
Strongly cemented
Indurated
cs
ci
Much pressure is needed to deform a
block of the molded material
Soil material is noncoherent
Aggregates crush easily between thumb
and finger
Gentle pressure is required to crush
aggregates
Moderate pressure is required to crush
aggregates
Strong pressure is required to crush
aggregates
Aggregates cannot be broken by pressure
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
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.
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.
http://en.wikipedia.org/wiki/Soil_structure ….. Diunduh 28/2/2012
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
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.
….. Diunduh 28/2/2012
HIDRASI MINERAL
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.
….. Diunduh 28/2/2012
DISPERSI
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.
….. Diunduh 28/2/2012
PRESIPITASI = PENGENDAPAN
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.
http://en.wikipedia.org/wiki/Precipitation_%28chemistry%29 ….. Diunduh 28/2/2012
FLOKULASI
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).
http://en.wikipedia.org/wiki/Flocculation ….. Diunduh 28/2/2012
AGREGASI
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.
….. Diunduh 28/2/2012
AGREGATE
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
….. Diunduh 28/2/2012
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
Dr. Jim Walworth
Department of Soil, Water and
Environmental Science
University of Arizona
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.
FLOKULASI - AGREGASI
Flocculation is important because water moves mostly in
large pores between aggregates. Also, plant roots grow
mainly between aggregates.
Dr. Jim Walworth
Department of Soil, Water and
Environmental Science
University of Arizona
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 "wellaggregated" 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
DISPERSI AGREGAT MENJADI KERAK
PERMUKAAN
In all but the sandiest soils, dispersed clays plug soil pores
and impede water infiltration and soil drainage.
Dr. Jim Walworth
Department of Soil, Water
and Environmental Science
University of Arizona
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
MUATAN NEGATIF DI
PERMUKAAN
Most clay particles have a negative electrical charge.
Like charges repel, so clay particles repel one another.
Dr. Jim Walworth
Department of Soil, Water
and Environmental Science
University of Arizona
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
KATION SEBAGAI PEREKAT
A cation is a positively charged molecule. Common soil
cations include sodium (Na+), potassium (K+), magnesium
(Mg2+), and calcium (Ca2+).
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
Relative
Flocculating
Power
Ion
Sodium
Na+
1.0
Potassium
K+
1.7
Magnesium
Mg2+
27.0
Calcium
Ca2+
43.0
Sumber: Sumner and Naidu, 1998
KATION SEBAGAI
PEREKAT FLOKULE
Cations in water attract water molecules because of their
charge, and become hydrated.
(+
)
Water molecule
is polar: (+) on
one end, (-) on
the other end
(+
)
Hydrated
cation
+
()
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
SAR = Sodium Adsorption
Ratio
Dr. Jim Walworth
Department of Soil, Water
and Environmental Science
University of Arizona
The ratio of ‘bad’ to ‘good’ flocculators gives
an indication of the relative status of
these cations:
+
+
+
+
+
+
+
++++++
++++++++
Ca2+ and
Mg2+
Mathematically, this is expressed as
the ‘sodium adsorption ratio’ or SAR:
SAR =
[Na+
]
[Ca2+] + [Mg2+]
where concentrations are expressed in mmoles/L
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
STABILITAS AGREGAT
Aggregate stability (dispersion and flocculation)
depends on the balance (SAR) between (Ca2+ and Mg2+)
and Na+ as well as the amount of soluble salts (EC) in
the soil.
Dr. Jim Walworth
Department of Soil, Water
and Environmental Science
University of Arizona
+
+
+
++++++
+
++++++++
+
+
+
E
C
Lower EC
Flocculated
soil
Higher EC
Dispersed
soil
KATION PEREKAT FLOKULASI
Soil particles will flocculate if concentrations of (Ca2+ +
Mg2+) are increased relative to the concentration of Na+
(SAR is decreased).
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 (Ca2+ +
Mg2+) are decreased relative to the concentration of Na+
(SAR is increased).
E
C
Flocculated soil
Dispersed
soil
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.
E
C
Lower EC
Flocculated
soil
Higher EC
Dispersed
soil
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
Higher EC
Dispersed
soil
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”.
If soils are irrigated with clean
water (with low EC), soil EC will
decrease, which can destabilize
aggregates. Irrigation water will
infiltrate slowly.
Lower EC
E
C
Higher EC
Floccula
ted soil
E
C
Lower 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.
Higher EC
Dispers
ed soil
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.
Soil
Classification
EC SAR
Condition
Normal
<4
<13
Flocculated
Saline
>4
<13
Flocculated
Sodic
<4
>13
Dispersed
Saline-Sodic
>4
>13
Flocculated
KALSIUM DAN STABILITAS AGREGAT
Increasing soluble calcium improves aggregate stability in
soils with poor structure.
Gypsum
CaSO4
EC
Flocculated
soil
Dispersed
soil
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.
Ca2+ SO42-
Ca++
Ca++
- - - - - - - -
Na+ Na+ Na+
- +
Na
- - - Na+
Na+
Na+
Na+
Ca+
+
Na+
Ca++
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Sulfuric acid* can be used instead of gypsum on
calcareous (CaCO3 containing) soil only.
• Sulfuric acid dissolves calcium
carbonate in the soil
H2 SO4  CaCO3  CO2  H2 O  CaSO4
and makes gypsum!
*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.
Behavior of sodium and calcium attached to a clay particles.
(After Hanson et al., 1999).
http://waterquality.montana.edu/docs/methane/basics_highlight.shtml….. Diunduh
28/2/2012
FLOKULASI
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 .
http://www.ozcoasts.gov.au/glossary/def_e-h.jsp….. Diunduh 28/2/2012
FLOKULASI
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.
http://www.terragis.bees.unsw.edu.au/terraGIS_soil/sp_stability_indices.html…..
Diunduh 28/2/2012
FLOKULASI - AGREGASI
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.
http://www.terragis.bees.unsw.edu.au/terraGIS_soil/sp_stability_indices.html…..
Diunduh 28/2/2012
KOAGOLASI
atau FLOKULASI
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 PO43- 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.
http://chemistry.tutorvista.com/physical-chemistry/flocculation.html ….. Diunduh 28/2/2012
Coagulation Values of Electrolytes
Coagulation of Negatively Charged Colloids As2s3
Coagulation Positively Charged Colloids Fe(oh)3
http://chemistry.tutorvista.com/physical-chemistry/flocculation.html ….. Diunduh
28/2/2012
Elemental sulfur can also be
used as an alternative to
gypsum on calcareous soils
• Soil microbes convert sulfur into sulfuric acid
S  ½O2  CO2  2 H2 O  H2 SO4  CH2 O
– H2SO4 dissolves calcium carbonate and
makes gypsum
• Conversion to sulfuric acid takes time
– several weeks
– faster in warm soils
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
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.
http://en.wikipedia.org/wiki/Soil_structure ….. Diunduh 28/2/2012
MANFAAT PERBAIKAN STRUKTUR TANAH
1.
2.
3.
4.
The benefits of improving soil structure for the growth of
plants, particularly in an agricultural setting include:
reduced erosion due to greater soil aggregate strength
and decreased overland flow;
improved root penetration and access to soil moisture and
nutrients;
improved emergence of seedlings due to reduced crusting
of the surface and;
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.
http://en.wikipedia.org/wiki/Soil_structure ….. Diunduh 28/2/2012
GRANULE
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
http://en.wikipedia.org/wiki/Granules ….. Diunduh 28/2/2012
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
TATANAN SEPARATE TANAH
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
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
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)
http://www.landfood.ubc.ca/soil200/interaction/structure.htm ….. Diunduh 28/2/2012
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
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)
http://vro.dpi.vic.gov.au/dpi/vro/vrosite.nsf/pages/soilhealth_changing_soil_structure
….. Diunduh 28/2/2012
PENTINGNYA STRUKTUR TANAH
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)
http://vro.dpi.vic.gov.au/dpi/vro/vrosite.nsf/pages/soilhealth_soil_structure …..
Diunduh 28/2/2012
AGREGATE TANAH
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://saret.ifas.ufl.edu/publications/bsbc/chap6.htm ….. 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.
http://tedspeds.wordpress.com/raindrops/ ….. Diunduh 28/2/2012
Platy and spherical soil structure is common to the
surface soil horizons, blocky and columnar/prismatic
are associated with the deeper subsurface soil
horizons
• Structured
•
Non-Structured
– Single Grain
– 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
– Massive
….. Diunduh 28/2/2012
AGREGASI DAN PORI TANAH
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.
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 = ∑ xiwi
xi = mean diameter
wi = dry mass fraction
http://www.consumer.org.nz/reports/soil-quality/check-your-soil-condition….. Diunduh
28/2/2012
STABILITAS AGREGAT
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.
http://www.consumer.org.nz/reports/soil-quality/check-your-soil-condition….. Diunduh
28/2/2012
STABILITAS AGREGAT
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.
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.
http://ipmguidelines.org/FieldCrops/Chapters/CH02/CH02-5.aspx ….. Diunduh
10/3/2012
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 (Db) 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
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.
http://www.grovida.com/horticulture-guide/soil-structure.html ….. Diunduh 28/2/2012
SEGITIGA TEKSTUR TANAH
….. Diunduh 28/2/2012
BENTUK ATAU TIPE STRUKTUR TANAH
….. Diunduh 28/2/2012
PENGELOLAAN STRUKTUR TANAH
If your soil has structural problems, chances are it is weather-sensitive or
stress-prone due to difficulties in root development and soil exploitation. Wellmanaged 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.
http://www.omafra.gov.on.ca/english/environment/soil/structure.htm ….. Diunduh
PEMBENTUKAN KERAK TANAH
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.
http://www.omafra.gov.on.ca/english/environment/soil/structure.htm ….. Diunduh
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
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.
http://www.fao.org/docrep/R4082E/r4082e03.htm ….. Diunduh 28/2/2012
AGREGAT TANAH
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.
http://www.ctahr.hawaii.edu/mauisoil/a_factor_ts.aspx ….. Diunduh 28/2/2012
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 shrinkswell 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
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 "waterstable."
http://www.soilandhealth.org/01aglibrary/010117attrasoilmanual/010117attra.html…..
Diunduh 28/2/2012
DEGRADASI AGREGAT TANAH
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).
http://www.soilandhealth.org/01aglibrary/010117attrasoilmanual/010117attra.html…..
Diunduh 28/2/2012
AGREGASI PARTIKEL TANAH
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.
http://www.cnr.uidaho.edu/range456/readings/Heitschmidt_Stuth_Book/Chapter_6/C
hapter6.htm….. Diunduh 28/2/2012
STABILITAS AGREGAT
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).
….. Diunduh 28/2/2012
EFEK VEGETASI TERHADAP
STABILITAS AGREGAT
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.
….. Diunduh 28/2/2012
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
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
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 P2O5, 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.
http://www.noble.org/ag/soils/organicmatter/ ….. Diunduh 29/2/2012
Organic matter and structure relation
Relation between
OC and 2-4 mm
aggregates % for
the two
topographic
positions.
http://users.ictp.it/~pub_off/lectures/lns018/10Bricchi2.pdf ….. Diunduh 29/2/2012
Importance of Soil Bulk Density
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/cm3 and 2.0 g/cm3; root
penetration is severely impacted at bulk densities greater than 1.6 g/cm3.
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.
http://www.soilsurvey.org/tutorial/page10.asp…..
Diunduh 29/2/2012
STRUKTUR TANAH
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.
http://www.soilsurvey.org/tutorial/page9.asp#e….. Diunduh 29/2/2012
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 perekatorganik 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 (Ca2+), magnesium (Mg2+)
and aluminum (Al3+), (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.
The polyvalent cations (including Ca2+, Fe3+ and
Al3+) may also attract and bind with hydrophobic
(water repelling) humus molecules allowing them to
bind to clay surfaces. These clay-humus particles
bind with each other and with grains of silt to form
the smallest of the primary aggregates, perhaps as
small as 0.01 mm. These small particles aid greatly
in stabilizing the slightly larger (<0.25 mm)
microaggregates which consist of fine or very fine
sand grains, smaller clumps of silt grains, clay and
organic debris all bound together by root hairs,
organic root exudates, and fungal threads.
http://www.soilsurvey.org/tutorial/page9.asp#e….. Diunduh 29/2/2012
Physical-Chemical Processes
Do you remember that monovalent cations like sodium, Na+, have a
different effect on soil aggregation? The single positive charge on
sodium (combined with a relatively large ionic radius) means that
sodium is not very efficient at neutralizing negative charges on clay
and on organic matter; the attractive forces between the cation and
the negatively charged colloids are not great enough to overcome the
natural repulsion of one negatively charged clay platelet by another.
The clay is not able to flocculate, and the result is a layer of nearly
structureless soil. Soils in arid and semi-arid climates are often high in
sodium, and exhibit a characteristic structure close to the surface
called columnar structure, which severely limits air, water and root
penetration.
As a soil dries out, the clay platelets move closer
together and cause shrinking in soil volume. Cracks will
form along tiny zones of weakness, and over the course
of several wet/dry cycles this network of cracks becomes
better defined. Plant roots, as they repeatedly remove
water from the same vicinity, reinforce a drying pattern
and contribute to physical aggregation of the soil. The
process of freezing and thawing in the soil also
contributes to the drying process as ice crystals form.
And shrinking and swelling that results from wet-dry and
freeze-thaw cycles creates tiny cracks or fissures
(shrinking) and pressure (swelling) that break apart
structureless masses of clay to eventually form soil peds
or aggregates.
http://www.soilsurvey.org/tutorial/page9.asp#e….. Diunduh 29/2/2012
PROSES-PROSES BIOLOGIS
The most prominent of the biological processes are
burrowing activities of soil animals; the binding
activity of fine roots and fungal hyphae; and the
production of organic “glues” by microorganisms like
bacteria and fungi. Soil animals such as earthworms
move soil particles as they burrow through the
ground; plant roots will also do this.
Particles which come in close proximity to one
another are more likely to form aggregates; channels
created by plant roots or burrowing activity act like
large pores, breaking up clods and helping to define
larger structural units. Plant roots and fungal hyphae
exude sticky organic substances (called
polysaccharides) which physically cement soil
particles together. And as bacteria decompose
organic material they contribute their share of
polysaccharides and other organic glues. Consider
the fact that a single gram of surface soil (about one
teaspoonful) contains 109-1010 bacteria , and you can
see how these sticky by-products might affect soil
aggregation.
We mentioned the role or organic matter above in the
physical-chemical discussion, but organic matter
contributes in one other way. As a general rule, the
more organic matter the soil contains, the greater the
populations of microorganisms and other
decomposers.
http://www.soilsurvey.org/tutorial/page9.asp#e….. Diunduh 29/2/2012
DESCRIBING SOIL STRUCTURE
Many types or shapes of structure occur in soils. Other soils
have no true structure and are called structureless.
Certain deposits, for example sands in a sand dune, are
called single grain because there is little to no attraction
between sand grains.
On the other textural extreme, some clay soils occur as large
cohesive masses and are termed massive in structure. Many
soils, however, will exhibit definite and repeatable shapes that
we can describe with four general categories.
Granular structure is generally spherical in shape,
and sometimes resembles BBs. The aggregates
may be separated easily from one another, and the
outer surfaces do not fit well together (not like
jigsaw puzzle pieces). Aggregates can be <1 mm
to perhaps 10 mm in diameter. Granular structure
is most commonly found in surface horizons,
especially those enriched with organic matter (an A
horizon). Grassland vegetation and earthworm
activity encourage granular structure.
http://www.soilsurvey.org/tutorial/page9.asp#e….. Diunduh 29/2/2012
DESCRIBING SOIL STRUCTURE
Block-like structure is similar in shape to a cube: all dimensions are of
nearly equal length, and typically range from <5 mm to over 50 mm in
diameter. They are not formed individually, but take their shape from
surrounding peds. Angular blocky peds have sharp, well-defined
edges and their rectangular faces are distinct. When most of the
edges are somewhat rounded, the structure is described as
subangular blocky. Block-like structures most often occur in B
horizons (or the subsoil).
Prism-like structures are those that are longer
than they are wide. They are variable in height
from horizon to horizon and from soil to soil;
diameters (width) may range from <10 mm to
over 100 mm. Similar to the block-like
structures, prism-like structures take their
shape from surrounding peds. In fact, they are
often associated with swelling types of clays
and are commonly found in subsurface B
horizons. If the tops of the prisms are
horizontally flat and angular, the structure is
described as prismatic. In certain soils, the
prisms have rounded tops somewhat like a
biscuit; this is called columnar structure.
Columnar structure is associated with soils
high in sodium, common in arid and semi-arid
regions (remember the discussion above on
Na+ and structure?).
http://www.soilsurvey.org/tutorial/page9.asp#e….. Diunduh 29/2/2012
DESCRIBING SOIL STRUCTURE
The final structure shape is platy. Platy structure is characterized by
relatively thin (<1 mm to about 10 mm) horizontally oriented peds that
look like plates stacked one on top of another. It may occur in surface
or subsurface horizons as a natural product of soil formation or
development. Unlike other shapes, it may be inherited from a soil’s
parent material especially if it was deposited by water (alluvium,
flowing water; or lacustrine, lake water) or ice (glacial).
Grade describes the distinctness of the structure, and is combined
with the cohesion of the soil within units compared to the adhesion
between individual units. Terms that are used for grade are weak,
moderate and strong. If the structural grade is weak, aggregates
are barely observable in the soil profile. When peds are gently
disturbed (for example, shaking them gently between your hands)
the material parts into a mixture of whole and broken units. Weak
structure may be easily compromised by management activities.
With moderate grade the structural units are well formed and
easily distinguished in the soil profile. When disturbed, the
aggregates part into a mixture of mostly whole units, some broken
units, and some material that is not in structural units. Individual
peds will part from adjoining peds somewhat cleanly. When grade
is described as strong the structural units are clearly seen in the
profile and shape is easily identified. Peds separate cleanly from
other peds and retain their shape when disturbed by shaking.
http://www.soilsurvey.org/tutorial/page9.asp#e….. Diunduh 29/2/2012
. Structural class is the description of the size of the units.
Verbal descriptions have size ranges as seen below. The size
limits refer to the smallest dimension of any given structural
unit, for example the width of a prism or the thickness of a
plate.
hapes of Structures
Size
Classes
platy
(mm)
prismatic
and
columnar
(mm)
Very fine
<1
<10
<5
<1
Fine
1-2
10 - 20
5 - 10
1-2
Medium
2-5
20 - 50
10 - 20
2-5
Coarse
5 - 10
50 - 100
20 - 50
5 - 10
Very
coarse
>10
>100
>50
>10
blocky
(mm)
granular
(mm)
http://www.soilsurvey.org/tutorial/page9.asp#e….. Diunduh 29/2/2012
PENGARUH STRUKTUR TANAH
Soil pores are dependant on the size and shape of
soil structure. Pores are multi-access highways in
the soil for air, water and plant roots. They are
defined and controlled by soil structure. The larger
and straighter the pores are, the more efficient they
are at moving air and water through the soil.
Water movement is of course important for plant
growth, but also plays a role in the movement of
nutrients and other fine particulates around in the
soil (called translocation). Air movement through,
into and out of the soil is also crucial for both
plants and soil animals. Metabolic activities
(respiration) of all living creatures below the
surface create CO2 gas, but they need to consume
oxygen.
Plants can obtain oxygen from the above-ground
environment, but soil microorganisms are
dependant on the soil environment; oxygen must
be available below the surface for aerobic
organisms to survive.
Soils which are poorly aerated can experience a
build-up of toxic gases like methane (CH4) and
ethylene (C2H4); if gaseous exchange between the
atmosphere and the soil atmosphere occurs readily,
favorable environments can be maintained.
http://www.soilsurvey.org/tutorial/page9.asp#e….. Diunduh 29/2/2012
TIPE STRUKTUR TANAH
Granular structure occurs most often in surface soils and is at
that atmosphere/soil atmosphere interface. Fortunately,
granular structures offer the most pore space and some of the
largest pores of any structure. This is important for gas
exchange, water infiltration, and seedling root penetration.
Subangular blocky structure, usually found in subsoils but
which sometimes occurs at the surface, is somewhat similar
to granular.
Angular blocky structure tends to pack closer to adjoining
peds than does subangular blocky, so consequently is more
limiting to air and water movement.
Prismatic is similar to angular blocky, although the length of
the flow path (along the long vertical sides of the prisms) is
greater.
Columnar structure has more limitations. As mentioned
in discussions above, columnar structure occurs in soils
higher in sodium and is often near the surface. The
rounded tops of the structure are related to the
dispersing effects of the monovalent Na+ which prevents
clays from flocculating. This effectively seals the soil to
air and water movement in either direction, up or down.
Arid and semi-arid climates experience high volume
storm events, so the infiltration capabilities of the soil are
critical.
Platy structure has the least amount of pore space with
the highest degree of tortuosity.
http://www.soilsurvey.org/tutorial/page9.asp#e….. Diunduh 29/2/2012
EFEK PENGELOLAAN THD STRUKTUR
TANAH
Humans impact the soil in many different
ways. Additions of chemicals in the form of
fertilizer or waste material, removal of
vegetation, agriculture, construction, and
recreation all leave a mark on the soil
resource. Many of these activities impact the
structure of the soil, sometimes in positive
ways, sometimes negatively.
Additions of fertilizer to agricultural land can
have a positive effect on soil structure. By
increasing plant growth and quality, roots
help with stability of soil aggregates.
Applications of liming material (high in
calcium, a key player in flocculation)
encourage better structure and tilth.
Organic materials in the form of plant residue
or animal manure quickly decompose and
participate in the development of soil
aggregates, and also provide favorable
conditions for microorganisms.
http://www.soilsurvey.org/tutorial/page9.asp#e….. Diunduh 29/2/2012
EFEK PENGOLAHAN TANAH
Agricultural practices such as tillage introduce air into the soil
and physically break up the soil. By aerating the soil some
additional pores space is temporarily created, and organic
residues decompose at a faster rate. Under proper soil
moisture conditions, breaking up clods of soil with poor or
weak structure will increase the surface area and facilitate
aggregation. Conservation tillage practices have greater
benefits to the soil than conventional tillage. Under
conservation practices, the need for tillage is minimized and
plant residues are left on or near the soil surface.
Conventional tillage requires more frequent tilling. A primary
pass is made to turn plant residue several inches below the
surface. This is followed by secondary tillage operations such
as harrowing, which kills weeds and breaks up clods prior to
planting. After planting, the soil may again be tilled for weed
control and to break up any crusting of the surface soil. These
multiple passes can compact the soil and result in the
formation of a “plow pan” and platy structure.
The amount and size of pores will decrease in this zone with
concomitant air and water movement. With decreased rates of
infiltration, surface runoff and soil erosion become issues.
Plant roots have greater difficulty penetrating the platy
structure and compacted soil, and limited rooting depth can
affect plant survival. Irrigation, if not properly applied, can
compound this problem by breaking up aggregates,
increasing sodium content, and leaching clay.
http://www.soilsurvey.org/tutorial/page9.asp#e….. Diunduh 29/2/2012
Types of Soil Structures in Soils
Source: http://www.cst.cmich.edu/users/Franc1M/esc334/lectures/physical.htm…..
Diunduh 9/3/2012
Soil structure and water movement.
Sumber: http://cru.cahe.wsu.edu/CEPublications/eb1633/eb1633.html….. Diunduh
STRUCTURE OR MICROSTRUCTURE OF SOIL
Mineral grains, water and air can be disposed in many ways
forming that kind of material as we know as soil. Notion, in
geomechanics as we call structure or more correct microstructure
is used to describe geometry and relation of set grains and pores
between them. So, we could difference three groups of soil:
Large granular microstructure
Tiny granular microstructure
Cemented microstructure
Sumber: http://www.gf.uns.ac.rs/~wus/wus07/web6/structure_microstructure.html…..
Diunduh 9/3/2012
STRUKTUR TANAH
Soil structure is the arrangement of pores and fissures (porosity) within a
matrix of solid materials (soil particles and organic matter). The solid
materials bond and aggregate to give the pores and fissures. The
quantity, distribution and arrangement of pores determines water holding
capacity, infiltration, permeability, root penetration, and, respiration.
Only about 50% of soil is solid material. The remainder is pore space. It is
in these spaces that the action happens. Water is stored there.
Organisms live there. Organic matter and nutrients accumulate there.
The diagram (magnified about 20 times) demonstrates how solids and
pores might arrange in soil to give a porosity of 50 %.
Small pores within the aggregates provide storage and refuge. The larger
pores (and fissures) between the aggregates are the pathways for liquids,
gases, roots and organisms.
Sumber:
http://vro.dpi.vic.gov.au/dpi/vro/vrosite.nsf/pages/soilhealth_soil_structure…..
Diunduh 9/3/2012
SOIL STRUCTURE AND MACROPORES
What it is: Sand, silt and clay particles are the primary mineral
building blocks of soil. Soil structure is the combination or
arrangement of primary soil particles into aggregates. Using
aggregate size, shape and distinctness as the basis for
classes, types and grades, respectively, soil structure
describes the manner in which soil particles are aggregated.
Soil structure affects water and air movement through soil,
greatly influencing soil's ability to sustain life and perform
other vital soil functions.
Soil pores exist between and within aggregates and are
occupied by water and air. Macropores are large soil pores,
usually between aggregates, that are generally greater than
0.08 mm in diameter.
Macropores drain freely by gravity and
allow easy movement of water and air.
They provide habitat for soil organisms
and plant roots can grow into them. With
diameters less than 0.08 mm, micropores
are small soil pores usually found within
structural aggregates. Suction is required
to remove water from micropores.
Sumber: http://soilquality.org/indicators/soil_structure.html….. Diunduh 9/3/2012
BAHAN ORGANIK DAN AGREGAT TANAH
High residue and cover crops contribute
organic matter to soil, while no-till
management helps protect organic matter
and allow accumulation. Organic matter
provides food for earthworms and other
soil biota. All play a role in developing or
protecting soil structure and macropores
to help soil function at a high level.
Inset shows relationship of macro- and
micropores to soil aggregates.
Sumber: http://soilquality.org/indicators/soil_structure.html….. Diunduh 9/3/2012
KERUSAKAN STRUKTUR TANAH
Practices that lead to poor soil structure include:
Disturbance that exposes soil to the adverse effects
of higher than normal soil drying, raindrop and rill
erosion, and wind erosion
Conventional tillage and soil disturbance that
accelerates organic matter decomposition
Residue harvest, burning or other removal methods
that prevent accumulation of soil organic matter
Overgrazing that weakens range and forage plants
and leads to declining root systems, poor growth
and bare soil
Equipment or livestock
traffic on wet soils
Production and irrigation
methods that lead to salt
or sodium accumulation in
surface soils
Sumber: http://soilquality.org/indicators/soil_structure.html….. Diunduh 9/3/2012
AGREGASI
The opposite of aggregation is dispersion. In a
dispersed soil, each individual soil particle is
free to blow away with the wind or wash away
with over-land flow of water.
Microbial byproducts glue soil particles into
water-stable aggregates.
Sumber: ….. Diunduh 9/3/2012
Usually, microbial gums, polysaccharides and other secondary
metabolites can bind soil particles together to form aggregates,
somewhat like a lump of various particles. Spaces between
aggregates are called inter-aggregate pores, and spaces within
the aggregates intra-aggregate pores.
Sumber: http://blog.nus.edu.sg/yiuyan/2009/11/24/earth-environment/….. Diunduh
9/3/2012
AGREGAT TANAH DAN AKAR TANAMAN
Close-up view of a plant root.
A) The mucigel layer containing some bacteria and clay
particles on the outside of the root. Also shown is a
mycorrhizal fungus sending out its rootlike hyphae into the
soil.
B) B) Soil aggregates surrounded by thin films of water. Plant
roots take water and nutrients from these films. Also
shown is a larger aggregate made up of smaller
aggregates pressed together and held in place by the root
and hyphae.
Sumber: http://saret.ifas.ufl.edu/publications/bsbc/chap3.htm….. Diunduh 9/3/2012
AGREGAT MAKRO
Akar Tanaman dan Agregasi Tanah
Sumber:
http://www.bio.anl.gov/environmental_biology/terrestrial_ecology/CO2.html…..
Diunduh 10/3/2012
PROSES AGREGASI TANAH
Sumber: http://csite.ornl.gov/themes/themes.html….. Diunduh 10/3/2012
AGREGASI TANAH
Sumber: vzj.geoscienceworld.org….. Diunduh 10/3/2012
KEHANCURAN AGREGAT TANAH
Slaking and dispersion
Slaking is related to soil structure and particularly to structural
stability, which is the soil’s ability to retain aggregates and
pore spaces under various environmental conditions. Slaking
is the result of lack of organic matter.
Slaking is severe in some soils with low organic matter and
can occur within minutes of the soil becoming wet. When a
slaked soil dries, crusting (hardsetting) of the soil can occur.
This limits water infiltration and seedling emergence. The
hardsetting can be limited to the top few millimetres of soil or
can extend through the entire soil profile.
Slaking is the breakdown of aggregates into smaller
aggregates or single particles. It occurs when a dry clay soil
becomes wet. The clay swells and the air within the pore
spaces in the aggregates is compressed. This builds up
pressure, resulting in the ‘explosion’ of the aggregate
Sumber: http://www.dpi.vic.gov.au/agriculture/dairy/pastures-management/fertilisingdairy-pastures/chapter-4….. Diunduh 10/3/2012
DISPERSI AGREGAT TANAH
Dispersion is usually a problem of soil chemistry (namely, high levels
of exchangeable sodium), although it can occur in non-sodic soils due
to excessive mechanical disturbance of the soil. Slaking and
dispersion can occur together. When this happens, both problems will
have to be managed.
Dispersion is the separation of the clay particles from the aggregates
when the soil is wet (see Figure 4.1). Clay particles carry a negative
electrical charge and tend to repel each other. Calcium, magnesium,
sodium and potassium all carry positive charges and are attracted to
the clay particles, forming a ‘bridge’, or bond, between the negatively
charged clay particles.
Calcium (Ca++) ions, followed by magnesium (Mg++) ions, are the
strongest ‘bridge formers’ because they have two positive charges.
Potassium (K+) and sodium (Na+) ions only have one positive
charge, and their bonding of the clay particles is much weaker. If
calcium is forming the bridge, the clay particles will hold together
when they are wet. However, if sodium is forming the bridge, the
bonding is much weaker and the clay particles tend to separate and
repel one another when they are wet (in other words, they tend to
disperse).
Cloudy or muddy water in puddles is an indication that a soil may be
dispersive. A continual stream of cloudy water running out of a mole
drain outlet is also indicative of a dispersive clay-type soil. Mole
drainage and open drains in dispersive soils may lead to severe soil
erosion.
When dispersion occurs, the dispersed clay particles fill up the pores
between soil particles and aggregates; and when the soil dries out,
the dispersed clay blocks up soil pores. This restricts seedling
emergence, water and air movement, and root penetration. Dispersed
soils are generally hardsetting and may form a surface crust.
Dispersion with no slaking results in a ‘concrete-like’ lump being
formed.
Sumber: http://www.dpi.vic.gov.au/agriculture/dairy/pastures-management/fertilisingdairy-pastures/chapter-4….. Diunduh 10/3/2012
BAHAN ORGANIK TANAH DAN KEMANTAPAN
AGREGAT
Management of slaking soils
Slaking, which is related to soil structure and particularly to
soil stability, can be managed by increasing the level of
organic matter in the soil. Organic matter reduces slaking by
reducing the rate of aggregate wetting and by more strongly
binding the soil particles together.
The best ways to increase the organic matter level in the
soil are to:
Grow highly productive pastures, especially perennial
ryegrass and white clover and, where possible, deep-rooted
legumes, such as lucerne.
Use minimum tillage techniques for crop and pasture
establishment.
Organic matter levels and stable soil aggregates can be easily
destroyed by excessive cultivation, by cultivation when the
soil is too dry or too wet, or by stock trampling, particularly
when the soils are wet. Cultivation increases the rate at which
organic matter oxidises from the soil.
The cultivation machinery compacts the soil, as does stock
trampling. In fine-textured soils, cultivating when the soil is too
wet breaks down aggregates, and cultivating when the soil is
too dry creates large clods that are not easily penetrated by
roots or seedlings.
Sumber: http://www.dpi.vic.gov.au/agriculture/dairy/pastures-management/fertilisingdairy-pastures/chapter-4….. Diunduh 10/3/2012
MANAGEMENT OF DISPERSIVE SOILS
In the short term, gypsum will reduce dispersion on sodic
soils. Lime can be used to reduce dispersion (to a lesser
extent) on acidic sodic soils, but it is much less soluble than
gypsum. In both cases, the sodium cations attached to clay
particles are replaced with the stronger-bonding calcium
cations. (Some magnesium cations will also be replaced by
calcium cations.) The clay particles then bond together, or
aggregate, by flocculation.
However, aggregates formed solely by flocculation generally
are not very stable. In the longer term, dispersion
management involves increasing the organic matter level in
the soil, which will help to form stable aggregates (aggregates
that hold together).
The sodium cations that are
exchanged for calcium
cations on the clay particles
don’t disappear. They enter
the soil solution, where they
can reattach to clay particles
when the opportunity arises.
Adequate drainage will give
longer-term responses to
gypsum applications.
Sumber: http://www.dpi.vic.gov.au/agriculture/dairy/pastures-management/fertilisingdairy-pastures/chapter-4….. Diunduh 10/3/2012
Soil Particle size
Any soil will be composed of a variety of particle sizes
ranging from large gravel particles down to tiny grains
of clay.
Sumber:
http://www.westone.wa.gov.au/toolbox6/hort6/html/resources/depot/hort_file/soil_stru
ct/soil_struct.html….. Diunduh 10/3/2012
Pore spaces
Soil particles do not fit together snugly. There are spaces
between particles. These spaces are called pore spaces and
contain water and air.
The pore spaces provide the route for the downward
movement of water and allow roots to grow into them. They
also provide air space, which is essential for plant growth.
The larger the pore spaces the better the drainage of water
and the less water retained in the soil. Conversely, the smaller
the pore spaces the less water drains away and the more
water is retained in the soil.
Sumber:
http://www.westone.wa.gov.au/toolbox6/hort6/html/resources/depot/hort_file/soil_stru
ct/soil_struct.html….. Diunduh 10/3/2012
AGREGAT TANAH
The diagram shows a soil particle, with the mineral element
being held together by organic matter and microbes. Soil
nutrient reserves are locked in the organic and mineral
fractions of the soil. The plant-available nutrition is held by
very fine clay colloids and humus.
Humus plays a central role in soil fertility, having the ability to
improve aeration and drainage, soil stability, ease of
cultivation, nutrient availability and microbial activity. Humus is
made by microbes as they decompose organic matter, and
has many soil-improving properties.
Humus increases the nutrient holding capacity of the soil, acts
as a natural chelating agent for micro-nutrients and reduces
the toxic effects of pollutants. Soils with good levels of humus
warm up quicker, encouraging the activity of roots and
beneficial micro-organisms.
Sumber: http://www.waternet.co.uk/waternet/soilfertilitypart1.htm ….. Diunduh
10/3/2012
The pore sizes vary and mayor may not be
filled with water.
The ratio of volume of the pore space to
the total volume of the soil or rock is called
porosity.
Sumber: http://www.globalsecurity.org/military/library/policy/army/fm/5484/Ch2.htm….. Diunduh 10/3/2012
The structure of soils is of the utmost importance. With
each increase in the degree of orderliness of the
structure, the physical properties of the soil aeration,
water permeability, etc are improved.
When comparing these properties of the structured and
structureless soil, Remezov (1952) of the
Dolgoprudnoya Experimental Station gave the following
figures:
Porosity
General porosity
Capillary
porosity
Noncapillary
porosity
Air content
Water
permeability
(in mm/hr)
In structureless
In structured soil,
soil,
%
%
50
55-60
45-48
20-25
2-5
30-35
5
30-40
3-5
20-25
1.6
0.7
Sumber: Remezov, N.P., Pochvy, ikh svoistva i rasprostranenie (Soils, their
Properties and Distribution).--Moscow, 1952.