STRUKTUR TANAH DAN AGREGASI ( S oemarno , Maret 2012)

1. STRUKTUR TANAH DAN AGREGASI(Soemarno, Maret2012) Mengapajalanaspaliniretak-retak? FOTO: smno.kampus.ub.jan2013

2. 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

3. 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

4. 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

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

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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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.

24. 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

25. 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

26. 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

27. + 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

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

29. (+) Water molecule is polar: (+) on one end, (-) on the other end (+) Hydrated cation + (-) 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.

30. ++ ++ ++ ++ ++ ++ ++ [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

31. 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

32. EC Lower EC Higher EC ++ ++ ++ ++ ++ ++ ++ Flocculated soil Dispersed soil + + + + + + + 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

33. KATION PEREKAT FLOKULASI Soil particles will flocculate if concentrations of (Ca2+ + Mg2+) are increased relative to the concentration of Na+ (SAR is decreased). + + + EC ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ Dr. Jim Walworth Department of Soil, Water and Environmental Science University of Arizona Na+ Ca2+ and Mg2+ SAR Flocculated soil Dispersed soil

34. Na dan DISPERSI Soil particles will disperse if concentrations of (Ca2+ + Mg2+) are decreased relative to the concentration of Na+ (SAR is increased). + + + + + + EC + ++ ++ ++ Flocculated soil Dispersed soil Ca2+ and Mg2+ Na+ SAR

35. 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 ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ + + + + + + + Flocculated soil Dispersed soil

36. DISPERSI Soil particles may disperse if the amount of soluble salts in the soil is decreased (i.e. if EC is decreased). EC ++ ++ ++ Flocculated soil Dispersed soil + + + Ca2+ and Mg2+ Na+ SAR Lower EC Higher EC

37. 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. + + + + + + + Ca2+ and Mg2+ SAR ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ EC ++ ++ Higher EC Lower EC Ca2+ and Mg2+ Flocculated soil ++ ++ ++ Na+ SAR + EC + + Higher EC Lower EC Dispersed soil

38. 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.

39. KALSIUM DAN STABILITAS AGREGAT Increasing soluble calcium improves aggregate stability in soils with poor structure. + + + EC ++ ++ ++ ++ ++ ++ ++ ++ Gypsum Na+ CaSO4 Ca2+ SO42- SAR ++ ++ Flocculated soil Dispersed soil

40. 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.

41. 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.

42. 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

43. 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

44. 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

45. 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

46. 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

47. 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

48. 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

49. 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.

50. 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