Bahan Kajian MK. Dasar Ilmu Tanah
AGREGASI
TANAH
FOTO: smno.kampus.ub.jan2013
Smno.jurtnh.fpub.des2013
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.
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
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
STRUKTUR TANAH:
Na dan Garam-garam
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
"well-aggregated" and this condition is thought to be very desirable, for a number of reasons. The aggregates are made up
of particles of different sizes and some of these particles fit closely together. Some do not. This means that there are
spaces of many different sizes in the soil and these spaces are essential for storing air, water, microbes, nutrients and
organic matter. http://www.soilhealth.com/biology/formation.htm
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.
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
Relative
Flocculating Power
Ion
Sodium
Na+
1.0
We can divide cations into two
categories
– Poor flocculators
• Sodium
Potassium
K+
1.7
Magnesium
Mg2+
27.0
Calcium
Ca2+
43.0
Sumber: Sumner and Naidu, 1998
– Good flocculators
• Calcium
• Magnesium
KATION SEBAGAI PEREKAT FLOKUL
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:
+
+
+
+
+
+
+
++ ++ ++
++ ++ ++ ++
Mathematically, this is expressed as
the ‘sodium adsorption ratio’ or SAR:
[Na+]
SAR =
[Ca2+] + [Mg2+]
where concentrations are expressed in mmoles/L
Ca2+ and Mg2+
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
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.
• Observasi Tanah di Lapangan.
– 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.
• Analisis Contoh Tanah.
– 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.
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.
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.
http://en.wikipedia.org/wiki/Soil_structure ….. Diunduh 28/2/2012
STRUKTUR TANAH
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
The benefits of improving soil structure for the growth of plants, particularly
in an agricultural setting include:
1. reduced erosion due to greater soil aggregate strength and decreased
overland flow;
2. improved root penetration and access to soil moisture and nutrients;
3. improved emergence of seedlings due to reduced crusting of the surface
and;
4. greater water infiltration, retention and availability due to improved
porosity.
It has been estimated that productivity from irrigated perennial horticulture
could be increased by two to three times the present level by improving soil
structure, because of the resulting access by plants to available soil water and
nutrients (Cockroft & Olsson, 2000, cited in Land and Water Australia 2007).
The NSW Department of Land and Water Conservation (1991) infers that in
cropping systems, for every millimetre of rain that is able to infiltrate, as
maximised by good soil structure, wheat yields can be increased by 10 kg/ha.
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=2E7B554DF79646147F64C3704857B3EF&article_id=2EB
7FE10AB38F7F2E7741544C2737396 ….. Diunduh 10/3/2012
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=2E7B554DF79646147F64C3704857B3EF&article_id=2EB
7FE10AB38F7F2E7741544C2737396 ….. 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=2E7B554DF79646147F64C3704857B3EF&article_id=2EB
7FE10AB38F7F2E7741544C2737396 ….. 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 welldefined 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
cementation: stabilization of
remain close together due to
floccules by action of a cementing
interactive forces (electrostatic, van
agent such (organic compounds,
der Waals, and/or hydrogen
carbonates, Fe and Al oxides, clays)
bonding) and form microscopic
floccules
http://www.landfood.ubc.ca/soil200/interaction/structure.htm ….. 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
….. Diunduh 28/2/2012
AGREGASI DAN PORI TANAH
Aggregate size
distribution also
influences the pore size
distribution.
Macropores: Interaggregate cavities that
influence infiltration,
drainage, and aeration.
Micropores: Intraaggregate 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 wetsieving (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=2E7B554DF79646147F64C3704857B3EF&article_id=2EB
7FE10AB38F7F2E7741544C2737396 ….. 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. Well-managed soils are
productive, even under difficult growing
conditions.
To maintain yields, short-term solutions are
often used (such as extra fertilizer, better
hybrids, and irrigation), even though poor soil
structure is the main problem.
There are four main types of soil structure
problems that occur across a range of soil
types in Ontario:
crusting
compaction
under-consolidation
setting-up.
Soils farmed with modern agriculture rarely
appear like the ideal soil. The processes of
tilage, crop seeding, and harvesting tend to
destroy aggregates and create a platy or
compacted layer. Note how the bulk density
increases in the compacted areas, and the
impact on crop rooting.
http://www.omafra.gov.on.ca/english/environment/soil/structure.htm ….. Diunduh 28/2/2012
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.
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 28/2/2012
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.
Crop Symptoms
1. crop growth can be slow, stunted, and variable, particularly under
stressful weather conditions
2. root tips are flattened and/or swollen
3. roots below compacted layer grow normally
4. root growth is concentrated along face of soil clods
5. crop may exhibit various nutrient deficiencies
6. roots tend to grow sideways or down large- sized holes/cracks
7. roots aren't penetrating evenly into the soil.
http://www.omafra.gov.on.ca/english/environment/soil/structure.htm ….. Diunduh 28/2/2012
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.
Best Management Practices
1. timely tillage and field operations - stay off wet fields; soil should be at
proper moisture conditions at tillage depth
2. good drainage - tile drainage should be installed in fields with variable
drainage
3. longer crop rotations that include forages/cereals
4. forage crops - leave in for longer than 1 year
5. tillage equipment - ensure it lifts and shatters soil (coulter chisel, cultivator)
as opposed to pulverizing and grinding (disk)
6. alternate tillage depth so that tillage pans aren't created
7. limit the amount of traffic, including tillage, across a field
8. 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 shrink-swell potential. This means that the
soil minerals expand, or swell, when wet, causing the soil to
become sticky and drain poorly. When dry, these soils shrink
and form cracks. The make-up of the lattice structure of
silicate clays determines the shrink-swell potential.
http://www.ctahr.hawaii.edu/mauisoil/a_factor_ts.aspx ….. Diunduh 28/2/2012
PEMBENTUKAN AGREGAT TANAH
Microbial byproducts glue soil particles into waterstable 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 byproducts cement the soil particles together forming
water-stable aggregates. The aggregate is then
strong enough to hold together when wet–hence the
name "water-stable."
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.
2.
3.
4.
5.
excessive tillage
working the soil when it is too wet or too dry
use of anhydrous ammonia that speed decomposition of organic matter
excess nitrogen fertilization
allowing build up of excess sodium from salty irrigation water or sodiumcontaining 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/Chapter6.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
http://grdc.com.au/director/events/grdcpublications.cfm?item_id=2E7B554DF79646147F64C3704857B3EF&article_id=2EB
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
http://www.noble.org/ag/soils/organicmatter/
….. Diunduh 29/2/2012
formation caused by
organic matter.
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 perekat-organik oleh mikro-organisme tanah.
http://www.soilsurvey.org/tutorial/page9.asp#e….. Diunduh 29/2/2012
Physical-Chemical Processes
Positively charged ions such as calcium (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.
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. 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)
blocky
(mm)
granular
(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
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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
for
http://www.soilsurvey.org/tutorial/page9.asp#e…..
Diunduhconditions
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.
http://www.soilsurvey.org/tutorial/page9.asp#e….. Diunduh 29/2/2012
EFEK PENGOLAHAN TANAH
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
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.
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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) 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/fertilising-dairy-pastures/chapter-4….. Diunduh
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).
Sumber: http://www.dpi.vic.gov.au/agriculture/dairy/pastures-management/fertilising-dairy-pastures/chapter-4….. Diunduh
10/3/2012
DISPERSI AGREGAT TANAH
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/fertilising-dairy-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/fertilising-dairy-pastures/chapter-4….. Diunduh
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_struct/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_struct/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 plantavailable 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