AGREGASI TANAH

1. AGREGASI TANAH BahanKajian MK. DasarIlmu Tanah Smno.jurtnh.fpub.des2013 FOTO: smno.kampus.ub.jan2013

2. 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

3. 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

4. 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

5. 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

6. 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.

7. 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

8. AGREGASI 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

9. 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

10. 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. STRUKTUR TANAH: Na dan Garam-garam 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.

11. 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.

12. 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

13. 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

14. 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

15. + 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

16. KATION FLOKULASI We can divide cations into two categories • Poor flocculators • Sodium • Good flocculators • Calcium • Magnesium Sumber: Sumner and Naidu, 1998

17. (+) Water molecule is polar: (+) on one end, (-) on the other end (+) Hydrated cation + (-) KATION SEBAGAI PEREKAT FLOKUL 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.

18. ++ ++ ++ ++ ++ ++ ++ [Na+] SAR = [Ca2+] + [Mg2+] + + + + + + + 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. PENGELOLAAN STRUKTUR TANAH • Be aware of the quality of irrigation water. Water with high levels of sodium (high SAR) will tend to destabilize soil. • Have irrigation water analyzed for SAR and EC or ask your water provider for analyses. • If you have high sodium irrigation water, the water and/or the soil may need amendments such as gypsum or sulfuric acid. • Observasi Tanah diLapangan. • 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. • AnalisisContoh Tanah. • Laboratory analysis can tell you the soil EC and SAR or ESP.

25. STRUKTUR TANAH Soil structure describes the arrangement of the solid parts of the soil and of the pore space located between them. The structure depends on what the soil developed from. The practices that influence soil structure will decline under most forms of cultivation—the associated mechanical mixing of the soil compacts and shears aggregates and fills pore spaces; it also exposes organic matter to a greater rate of decay and oxidation. A further consequence of continued cultivation and traffic is the development of compacted, impermeable layers or pans within the profile. Soil structure decline under irrigation is usually related to the breakdown of aggregates and dispersion of clay material as a result of rapid wetting. This is particularly so if soils are sodic; that is, having a high exchangeable sodium percentage (ESP) of the cations attached to the clays. High sodium levels (compared to high calcium levels) cause particles to repel one another when wet and for the associated aggregates to disaggregate and disperse. The ESP will increase if irrigation causes salty water (even of low concentration) to gain access to the soil. http://en.wikipedia.org/wiki/Soil_structure ….. Diunduh 28/2/2012

26. STRUKTUR TANAH A wide range of practices are undertaken to preserve and improve soil structure. For example, the NSW Department of Land and Water Conservation, (1991) advocates: increasing organic content by incorporating pasture phases into cropping rotations; reducing or eliminating tillage and cultivation in cropping and pasture activities; avoiding soil disturbance during periods of excessive dry or wet when soils may accordingly tend to shatter or smear, and; ensuring sufficient ground cover to protect the soil from raindrop impact. In irrigated agriculture, it may be recommended to: apply gypsum (calcium sulfate) to displace sodium cations with calcium and so reduce ESP or sodicity; avoid rapid wetting, and; avoid disturbing soils when too wet or dry. http://en.wikipedia.org/wiki/Soil_structure ….. Diunduh 28/2/2012

27. 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

28. 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

29. 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 HumicGleysol (modified from Angers and Carter, 1996). http://grdc.com.au/director/events/grdcpublications.cfm?item_id=2E7B554DF79646147F64C3704857B3EF&article_id=2EB7FE10AB38F7F2E7741544C2737396 ….. Diunduh 10/3/2012

30. 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

31. 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

32. 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

33. 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

34. 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

35. 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

36. 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 actinomyceteshypha 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

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

38. 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

39. 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

40. 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

41. 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

42. 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

43. 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

44. BENTUK ATAU TIPE STRUKTUR TANAH ….. Diunduh 28/2/2012

45. 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

46. PEMBENTUKAN KERAK TANAH Following the rapid wetting and drying of an overworked seedbed, a solid sheet forms (0.2 to 5 centimetres thick) that is tight enough to prevent crop emergence. This is known as soil crusting. Best Management Practices 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

47. PEMADATAN TANAH Compaction is the process of increasing soil density by packing soil particles closer together. It can occur anywhere in the soil profile, but tends to be seen near the surface or at plow depth. Good management can lessen the impact of compaction on soil structure. Crop Symptoms 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. http://www.omafra.gov.on.ca/english/environment/soil/structure.htm ….. Diunduh 28/2/2012

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

49. 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

50. 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