Struktur tanah dan agregasi s oemarno maret 2012
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Struktur tanah dan agregasi s oemarno maret 2012

STRUKTUR TANAH DAN AGREGASI(Soemarno, Maret2012)

Mengapajalanaspaliniretak-retak?

FOTO: smno.kampus.ub.jan2013


Struktur tanah dan agregasi s oemarno maret 2012

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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 2012

GRADE STRUKTUR TANAH

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

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


Struktur tanah dan agregasi s oemarno maret 2012

BENTUK STRUKTUR

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


Struktur tanah dan agregasi s oemarno maret 2012

UKURAN STRUKTUR

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


Struktur tanah dan agregasi s oemarno maret 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.

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

Sumber: ….. Dunduh 10/3/2012


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 2012

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

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 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


Struktur tanah dan agregasi s oemarno maret 2012

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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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.

Hydration occurs as clay packets absorb water and swell.

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.

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

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.

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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 2012

AGREGASI

Natural sciences and statistics:

Aggregation of soil granules to form soil structure

Particle aggregation, direct mutual attraction between particles (atoms or molecules) via van der Waals forces or chemical bonding

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

Flocculation, a process where a solute comes out of solution in the form of floc or flakes

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

Aggregation pheromone

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


Struktur tanah dan agregasi s oemarno maret 2012

AGREGATE

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

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

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

In some Christian churches, a group of several canonical hours (offices) combined to form a single religious service

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

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

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

Aggregate analysis, a technique used in amortized analysis in computer science, especially in analysis of algorithms

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

Aggregate data, in statistics, data combined from several measurements

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

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

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

Aggregate score, in sport, the sum of two scorelines in a two-legged match

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

Aggregate species (Wiktionary) or Species aggregate, a named species representing a range of very closely related organisms

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

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

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.

Dr. Jim Walworth

Department of Soil, Water and Environmental Science

University of Arizona


Struktur tanah dan agregasi s oemarno maret 2012

FLOKULASISoil 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.


Struktur tanah dan agregasi s oemarno maret 2012

FLOKULASI - AGREGASIFlocculation 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


Struktur tanah dan agregasi s oemarno maret 2012

DISPERSI AGREGAT MENJADI KERAK PERMUKAANIn 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


Struktur tanah dan agregasi s oemarno maret 2012

MUATAN NEGATIF DI PERMUKAANMost 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


Struktur tanah dan agregasi s oemarno maret 2012

+

KATION SEBAGAI PEREKATA 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

KATION FLOKULASI

  • We can divide cations into two categories

    • Poor flocculators

      • Sodium

    • Good flocculators

      • Calcium

      • Magnesium

Sumber: Sumner and Naidu, 1998


Kation sebagai perekat flokule

(+)

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

(+)

Hydrated cation

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(-)

KATION SEBAGAI PEREKAT FLOKULE

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

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


Sar sodium adsorption ratio

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[Na+]

SAR =

[Ca2+] + [Mg2+]

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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:

Na+

Ca2+ and Mg2+

Mathematically, this is expressed as

the ‘sodium adsorption ratio’ or SAR:

where concentrations are expressed in mmoles/L


Daya hantar listrik

DAYA HANTAR LISTRIK

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.

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.

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


Struktur tanah dan agregasi s oemarno maret 2012

EC

Lower EC

Higher EC

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Flocculated soil

Dispersed soil

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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

Na+

Ca2+ and Mg2+

SAR


Struktur tanah dan agregasi s oemarno maret 2012

KATION PEREKAT FLOKULASI

Soil particles will flocculate if concentrations of (Ca2+ + Mg2+) are increased relative to the concentration of Na+ (SAR is decreased).

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EC

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Dr. Jim Walworth

Department of Soil, Water and Environmental Science

University of Arizona

Na+

Ca2+ and Mg2+

SAR

Flocculated soil

Dispersed soil


Struktur tanah dan agregasi s oemarno maret 2012

Na dan DISPERSI

Soil particles will disperse if concentrations of (Ca2+ + Mg2+) are decreased relative to the concentration of Na+ (SAR is increased).

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EC

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Flocculated soil

Dispersed soil

Ca2+ and Mg2+

Na+

SAR


Struktur tanah dan agregasi s oemarno maret 2012

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.

Na+

Ca2+ and Mg2+

SAR

EC

Lower EC

Higher EC

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Flocculated soil

Dispersed soil


Struktur tanah dan agregasi s oemarno maret 2012

DISPERSI

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

EC

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Flocculated soil

Dispersed soil

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Ca2+ and Mg2+

Na+

SAR

Lower EC

Higher EC


Struktur tanah dan agregasi s oemarno maret 2012

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”.

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.

Na+

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

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Ca2+ and Mg2+

SAR

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EC

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Higher EC

Lower EC

Ca2+ and Mg2+

Flocculated soil

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Na+

SAR

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EC

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Higher EC

Lower EC

Dispersed soil


Struktur tanah dan agregasi s oemarno maret 2012

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.


Struktur tanah dan agregasi s oemarno maret 2012

KALSIUM DAN STABILITAS AGREGAT

Increasing soluble calcium improves aggregate stability in soils with poor structure.

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EC

++

++

++

++

++

++

++

++

Gypsum

Na+

CaSO4

Ca2+

SO42-

SAR

++

++

Flocculated soil

Dispersed soil


Struktur tanah dan agregasi s oemarno maret 2012

Ca2+

SO42-

Ca++

Ca++

-

-

-

-

-

-

-

-

-

Ca++

Ca++

Na+

Na+

Na+

-

-

-

-

Na+

-

-

-

-

-

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

GIPSUM UNTUK AGREGASI TANAHApply 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.


Sulfuric acid can be used instead of gypsum on calcareous caco 3 containing soil only

Sulfuric acid* can be used instead of gypsum on calcareous (CaCO3 containing) soil only.

  • Sulfuric acid dissolves calcium carbonate in the soil

    and makes gypsum!

*Sulfuric acid is extremely dangerous and should only be handled by trained personnel.


Struktur tanah dan agregasi s oemarno maret 2012

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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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 ofsoil 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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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

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

  • Soil microbes convert sulfur into sulfuric acid

    • H2SO4 dissolves calcium carbonate and makes gypsum

      • Conversion to sulfuric acid takes time

        • several weeks

        • faster in warm soils


Pengelolaan struktur tanah

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 dan agregasi s oemarno maret 2012

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


Struktur tanah dan agregasi s oemarno maret 2012

MANFAAT PERBAIKAN STRUKTUR TANAH

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


Struktur tanah dan agregasi s oemarno maret 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.

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

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

"Azurophil granule", a structure characteristic of the azurophileukarytotic cell type

"Chromaffin granule", a structure characteristic of the chromophil eukaryotic cell type

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

Granule (geology), a specified particle size of 2–4 millimetres (-1–-2 on the φ scale)

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

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

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


Struktur tanah dan agregasi s oemarno maret 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=2EB7FE10AB38F7F2E7741544C2737396 ….. Diunduh 10/3/2012


Struktur tanah dan agregasi s oemarno maret 2012

….. Diunduh 28/2/2012


Struktur tanah dan agregasi s oemarno maret 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=2EB7FE10AB38F7F2E7741544C2737396 ….. Diunduh 10/3/2012


Struktur tanah dan agregasi s oemarno maret 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=2EB7FE10AB38F7F2E7741544C2737396 ….. Diunduh 10/3/2012


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 2012

AGREGASI = Formation of Aggregates

aggregation = flocculation + cementation

Flocculation is the first step in aggregate formation. 

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


Struktur tanah dan agregasi s oemarno maret 2012

Aggregate Formation: Illustration of several levels in aggregate formation 

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


Struktur tanah dan agregasi s oemarno maret 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

TillageCultivation practices

Re-forming soils Laser levelling

Raised beds

Contour banks and terracing

Gypsum for responsive soils

Subsoil managementControlled 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


Struktur tanah dan agregasi s oemarno maret 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):

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

Permeability (to represent infiltration, drainage and respiration)

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

Soil strength (to represent toughness and resilience of structures)

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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 2012

Non-Structured

Single Grain

Massive

Structured

Platy: horizontal & flat

Spherical (Grannular): rounded and <2.0 cm

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

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

….. Diunduh 28/2/2012


Struktur tanah dan agregasi s oemarno maret 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

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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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

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=2E7B554DF79646147F64C3704857B3EF&article_id=2EB7FE10AB38F7F2E7741544C2737396 ….. Diunduh 28/2/2012


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 2012

SEGITIGA TEKSTUR TANAH

….. Diunduh 28/2/2012


Struktur tanah dan agregasi s oemarno maret 2012

BENTUK ATAU TIPE STRUKTUR TANAH

….. Diunduh 28/2/2012


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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.

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

reduce secondary tillage; don't overwork the soil

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

use a good crop rotation - include grasses and legumes where possible

use cover crops

use manure management to build soil organic matter

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

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

check plant populations: replant as a last resort

a light rain will help soften the crust.

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


Struktur tanah dan agregasi s oemarno maret 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.

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 dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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 "water-stable."

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


Struktur tanah dan agregasi s oemarno maret 2012

DEGRADASI AGREGAT TANAH

Some factors which destroy or degrade soil aggregates are:

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 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


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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.

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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).

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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:

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.

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.

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.

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Struktur tanah dan agregasi s oemarno maret 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=2E7B554DF79646147F64C3704857B3EF&article_id=2EB7FE10AB38F7F2E7741544C2737396


Struktur tanah dan agregasi s oemarno maret 2012

What Are the Benefits of Organic Matter? Nutrient SupplyOrganic 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 CapacityOrganic 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 AggregationOrganic 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 PreventionThis 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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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 dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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


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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


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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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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


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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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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.

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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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 2012

Types of Soil Structures in Soils

Source: http://www.cst.cmich.edu/users/Franc1M/esc334/lectures/physical.htm….. Diunduh 9/3/2012


Struktur tanah dan agregasi s oemarno maret 2012

Soil structure and water movement.

Sumber: http://cru.cahe.wsu.edu/CEPublications/eb1633/eb1633.html….. Diunduh 9/3/2012


Struktur tanah dan agregasi s oemarno maret 2012

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 dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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 structuredescribes 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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 2012

AGREGAT TANAH DAN AKAR TANAMAN

  • Close-up view of a plant root.

  • The mucigel layer containing some bacteria and clay particles on the outside of the root. Also shown is a mycorrhizal fungus sending out its rootlikehyphae 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


Struktur tanah dan agregasi s oemarno maret 2012

AGREGAT MAKRO

Akar Tanaman dan Agregasi Tanah

Sumber: http://www.bio.anl.gov/environmental_biology/terrestrial_ecology/CO2.html….. Diunduh 10/3/2012


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PROSES AGREGASI TANAH

Sumber: http://csite.ornl.gov/themes/themes.html….. Diunduh 10/3/2012


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AGREGASI TANAH

Sumber: vzj.geoscienceworld.org….. Diunduh 10/3/2012


Struktur tanah dan agregasi s oemarno maret 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 10/3/2012


Struktur tanah dan agregasi s oemarno maret 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/fertilising-dairy-pastures/chapter-4….. Diunduh 10/3/2012


Struktur tanah dan agregasi s oemarno maret 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 10/3/2012


Struktur tanah dan agregasi s oemarno maret 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/fertilising-dairy-pastures/chapter-4….. Diunduh 10/3/2012


Struktur tanah dan agregasi s oemarno maret 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_struct/soil_struct.html….. Diunduh 10/3/2012


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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


Struktur tanah dan agregasi s oemarno maret 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/5-484/Ch2.htm….. Diunduh 10/3/2012


Struktur tanah dan agregasi s oemarno maret 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:

Sumber: Remezov, N.P., Pochvy, ikh svoistva i rasprostranenie (Soils, their

Properties and Distribution).--Moscow, 1952.


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