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AGREGASI TANAH FOTO: smno.kampus.ub.jan2013 Smno.jurtnh.fpub.des2013 Bahan Kajian MK. Dasar Ilmu Tanah.

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Presentation on theme: "AGREGASI TANAH FOTO: smno.kampus.ub.jan2013 Smno.jurtnh.fpub.des2013 Bahan Kajian MK. Dasar Ilmu Tanah."— Presentation transcript:

1 AGREGASI TANAH FOTO: smno.kampus.ub.jan2013 Smno.jurtnh.fpub.des2013 Bahan Kajian MK. Dasar Ilmu Tanah

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. ….. Diunduh 28/2/2012 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.granules

3 Soils may be non-structured (e.g., single grain or massive) or consist of naturally formed units known as peds or aggregates. The initial stage in the formation of soil structure is the process of flocculation. Individual colloids typically exhibit a net negative charge which results in an electrostatic repulsion. ….. Diunduh 28/2/2012

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 ….. Diunduh 28/2/2012 Clay-water interaction is an all-inclusive term to describe various progressive interactions between clay minerals and water. In the dry state, clay packets exist in face-to-face stacks like a deck of playing cards, but clay packets begin to change when exposed to water. Five descriptive terms describe the progressive interactions that can occur in a clay-water system, such as a water mud. 1.Hydration occurs as clay packets absorb water and swell. 2.Dispersion (or disaggregation) causes clay platelets to break apart and disperse into the water due to loss of attractive forces as water forces the platelets farther apart. 3.Flocculation begins when mechanical shearing stops and platelets previously dispersed come together due to the attractive force of surface charges on the platelets. 4.Deflocculation, the opposite effect, occurs by addition of chemical deflocculant to flocculated mud; the positive edge charges are covered and attraction forces are greatly reduced. 5.Aggregation, a result of ionic or thermal conditions, alters the hydrational layer around clay platelets, removes the deflocculant from positive edge charges and allows platelets to assume a face-to-face structure.

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 ….. Diunduh 28/2/2012 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.settlefiltered 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).

8 AGREGASI ….. Diunduh 28/2/ Aggregation of soil granules to form soil structure 2.Particle aggregation, direct mutual attraction between particles (atoms or molecules) via van der Waals forces or chemical bonding 3.The accumulation of platelets to the site of a wound to form a platelet plug or a thrombus 4.Flocculation, a process where a solute comes out of solution in the form of floc or flakes 5.Overdispersion or statistical aggregation, where the variance of a distribution is higher than expected 6.Aggregation pheromone 7.Protein aggregation, the aggregation of mis-folded proteins Particle aggregation in materials science is direct mutual attraction between particles (atoms or molecules) via van der Waals forces or chemical bonding. Particle aggregation is often spontaneous and involves one particle attaching to another particle or existing aggregate of particles. Particle aggregation occurs when particles come into close contact with each other. When there are collisions between particles in fluid, there is a chance that particles will attach to each other and become larger particle. There are 3 major physical mechanisms to form aggregate: Brownian motion, Fluid shear and differential settling.

9 AGREGATE An aggregate is a collection of items that are gathered together to form a total quantity. 1.Aggregate (composite), in materials science, a component of a composite material used to resist compressive stressAggregate (composite) 2.Construction aggregate, materials used in construction, including sand, gravel, crushed stone, slag, or recycled crushed concreteConstruction aggregate 3.In some Christian churches, a group of several canonical hours (offices) combined to form a single religious servicecanonical hours 4.In the social sciences, a gathering of people into a cluster or a crowd that do not form a true social groupsocial group 5.In music, a set of all twelve pitch classes, also known as the total chromatictotal chromatic 6.Aggregate (Sanskrit, skandha; Pāli, khandha), in Buddhism, refers to a category of sensory experiencesskandha 7.Aggregate analysis, a technique used in amortized analysis in computer science, especially in analysis of algorithmsamortized analysis 8.Aggregate (data warehouse), a part of the dimensional model that is used to speed up query time by summarizing tablesAggregate (data warehouse) 9.Aggregate data, in statistics, data combined from several measurementsAggregate data 10.Aggregate demand, the total demand for final goods and services during a specific time period in an economyAggregate demand 11.Aggregate supply, the total supply of goods and services produced during a specific time period in an economyAggregate supply 12.Aggregate function, in computer science (especially SQL), a function that calculates a single result (scalar) from a collection of input valuesAggregate function 13.Aggregate score, in sport, the sum of two scorelines in a two-legged matchAggregate score 14.Aggregate (rocket family), in rocketry, a set of experimental rocket designs developed in Nazi GermanyAggregate (rocket family) 15.Aggregate species (Wiktionary) or Species aggregate, a named species representing a range of very closely related organismsAggregate species (Wiktionary) 16.Aggregate Spend (US), a process to monitor the total amount spent by healthcare manufacturers on individual healthcare professionals and organizations through payments and gifts of various kindsAggregate Spend 17.AggreGate Platform, a software framework for managing diverse electronic devicesAggreGate Platform Aggregate RootAggregate Root, Domain Driven Design conceptDomain Driven Design

10 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.

11 FLOKULASI Soil clay particles can be unattached to one another (dispersed) or clumped together (flocculated) in aggregates. Soil aggregates are cemented clusters of sand, silt, and clay particles. Dispersed ParticlesFlocculated Particles 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. Dr. Jim Walworth Department of Soil, Water and Environmental Science University of Arizona

12 FLOKULASI - AGREGASI Flocculation is important because water moves mostly in large pores between aggregates. Also, plant roots grow mainly between aggregates. 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. Dr. Jim Walworth Department of Soil, Water and Environmental Science University of Arizona

13 DISPERSI AGREGAT MENJADI KERAK PERMUKAAN In all but the sandiest soils, dispersed clays plug soil pores and impede water infiltration and soil drainage. 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. Dr. Jim Walworth Department of Soil, Water and Environmental Science University of Arizona

14 MUATAN NEGATIF DI PERMUKAAN Most clay particles have a negative electrical charge. Like charges repel, so clay particles repel one another. 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. Dr. Jim Walworth Department of Soil, Water and Environmental Science University of Arizona

15 KATION SEBAGAI PEREKAT A cation is a positively charged molecule. Common soil cations include sodium (Na + ), potassium (K + ), magnesium (Mg 2+ ), and calcium (Ca 2+ ). Cations can make clay particles stick together (flocculate). 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:

16 KATION FLOKULASI We can divide cations into two categories –Poor flocculators Sodium –Good flocculators Calcium Magnesium Ion Relative Flocculating Power SodiumNa PotassiumK+K+ 1.7 MagnesiumMg CalciumCa Sumber: Sumner and Naidu, 1998

17 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. CationCharges per moleculeHydrated radius (nm) Relative flocculating power Sodium Potassium Magnesium Calcium Water molecule is polar: (+) on one end, (-) on the other end (+) (-) (+) Hydrated cation +

18 SAR = Sodium Adsorption Ratio The ratio of ‘bad’ to ‘good’ flocculators gives an indication of the relative status of these cations: Na Ca 2+ and Mg Mathematically, this is expressed as the ‘sodium adsorption ratio’ or SAR: where concentrations are expressed in mmoles/L SAR = [Na + ] [Ca 2+ ] + [Mg 2+ ] Dr. Jim Walworth Department of Soil, Water and Environmental Science University of Arizona

19 DAYA HANTAR LISTRIK Ions in solution conduct electricity, so the total amount of soluble soil ions can be estimated by measuring the electrical conductivity (EC) of a soil water extract. EC is measured in units of conductance over a known distance: deci-Siemens per meter or dS/m Soil with a high EC is salty; soil with a low EC is not. Electrical conductivity (EC) estimates the amount of total dissolved salts (TDS), or the total amount of dissolved ions in the SOIL solution. Soil electrical conductivity (EC) is a measurement that correlates with soil properties that affect crop productivity, including soil texture, cation exchange capacity (CEC), drainage conditions, organic matter level, salinity, and subsoil characteristics. Sumber:

20 FLOKULASI - AGREGASI Diunduh 28/2/2012 The process of flocculation alone, however, does not make aggregates stable. Various soil satabilising agents are also necessary for the particles to aggregate. This includes the presence of clay minerals, sesquioxides (i.e. aluminium- and iron-oxides) and humus. In the first instance, the negatively charged clay mineral surfaces can interact with each other and with sand and silt sized particles to form aggregates. In addition, oxides of iron also link particles because some having positive charges, while other oxides have no charge but can build up tough coatings that connect particles. Finally, large organic molecules tend to form bridges between mineral particles, either with electrostatic charge or by linking particles together like a net. Soil microorganisms provide the best cement because as they break down soil residues they produce gums that glue peds together. These stabilizing agents along with the processes of localised compression resulting from repeated cycles of soil wetting and drying, shrinking and swelling and the action of organisms (flora and fauna) result in the repeated compression of the same soil mass. This leads to the increased coherence of aggregates (peds) that are difficult to pull apart. The result is a well aggregated soil which contains large cracks or voids between the aggregated soil particles. These larger voids or macropores improve water infiltration, gaseous exchange and root penetration.

21 KOAGOLASI atau FLOKULASI ….. Diunduh 28/2/2012 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 PO 4 3- 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.

22 Coagulation Values of Electrolytes ….. Diunduh 28/2/2012 Coagulation of Negatively Charged Colloids As2s3 Coagulation Positively Charged Colloids Fe(oh)3

23 Elemental sulfur can also be used as an alternative to gypsum on calcareous soils Soil microbes convert sulfur into sulfuric acid –H 2 SO 4 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 di Lapangan. –If water infiltrates very slowly, or if rain water infiltrates more slowly than irrigation water, the soil may have a sodium problem. –Sodium impacted soils may noticeably crack when dry. Analisis Contoh Tanah. –Laboratory analysis can tell you the soil EC and SAR or ESP.

25 STRUKTUR TANAH ….. Diunduh 28/2/2012 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.

26 STRUKTUR TANAH ….. Diunduh 28/2/2012 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.

27 MANFAAT PERBAIKAN STRUKTUR TANAH ….. Diunduh 28/2/2012 The benefits of improving soil structure for the growth of plants, particularly in an agricultural setting include: 1.reduced erosion due to greater soil aggregate strength and decreased overland flow; 2.improved root penetration and access to soil moisture and nutrients; 3.improved emergence of seedlings due to reduced crusting of the surface and; 4.greater water infiltration, retention and availability due to improved porosity. It has been estimated that productivity from irrigated perennial horticulture could be increased by two to three times the present level by improving soil structure, because of the resulting access by plants to available soil water and nutrients (Cockroft & Olsson, 2000, cited in Land and Water Australia 2007). The NSW Department of Land and Water Conservation (1991) infers that in cropping systems, for every millimetre of rain that is able to infiltrate, as maximised by good soil structure, wheat yields can be increased by 10 kg/ha.

28 GRANULE ….. Diunduh 28/2/2012 Granule is a generic term used for a small particle or grain. The generic term is employed in a variety of specific contexts. 1.Granule (solar physics), visible structures in the photosphere of the Sun arising from activity in the Sun's convective zoneGranule (solar physics) 2.Granule (cell biology), any of several submicroscopic structures, some with explicable origins, others noted only as cell type-specific features of unknown functionGranule (cell biology) 3."Azurophil granule", a structure characteristic of the azurophil eukarytotic cell typeazurophil 4."Chromaffin granule", a structure characteristic of the chromophil eukaryotic cell typechromophil 5.Martian spherules, spherical granules of material found on the surface of the planet MarsMartian spherules 6.Granule (geology), a specified particle size of 2–4 millimetres (-1–-2 on the φ scale)Granule (geology) 7.In pharmaceutical terms, a granule is small particles gathered into a larger, permanent aggregate in which the original particles can still be identified 8.In the Oracle database, a unit of contiguously allocated virtual memoryOracle database

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 Humic Gleysol (modified from Angers and Carter, 1996). 7FE10AB38F7F2E C ….. Diunduh 10/3/2012

30 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). 7FE10AB38F7F2E C ….. Diunduh 10/3/2012 TATANAN SEPARATE TANAH

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). 7FE10AB38F7F2E C ….. 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 ….. Diunduh 28/2/2012 AGREGASI = Formation of Aggregates aggregation = flocculation + cementation Flocculation is the first step in aggregate formation. flocculation: when primary particles remain close together due to interactive forces (electrostatic, van der Waals, and/or hydrogen bonding) and form microscopic floccules cementation: stabilization of floccules by action of a cementing agent such (organic compounds, carbonates, Fe and Al oxides, clays)

34 PENTINGNYA STRUKTUR TANAH ….. Diunduh 28/2/2012 Soil is like a city The structure and layout of both determine how things happen, the rate at which they happen, and the capability to keep them happening. The following characteristics are used to help evaluate the ability of any soil to perform well (or otherwise): 1.Porosity (to represent aeration, water storage capacity, plant wilting point and drainage)Porosity 2.Permeability (to represent infiltration, drainage and respiration) 3.Bonding and aggregation (to represent how the solids group together and the construction materials used)Bonding and aggregation 4.Soil strength (to represent toughness and resilience of structures)Soil strength 5.Friability, tillage and trafficability (to represent how soils behave with mechanical disturbance)tillagetrafficability

35 AGREGATE TANAH ….. Diunduh 28/2/2012 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.

36 ….. Diunduh 28/2/2012 AGREGASI PARTIKEL TANAH Clay particles have a plate like shape. Domains are a number of clay particles stacked up together. The surfaces of clay particles are negatively charged and the electrostatic forces can form either attraction or repulsion forces between clay particles. Calcium ions increase attraction forces and the flocculation of clay particles. Sodium ions increase repulsion forces and the dispersion of clay particles. Organic colloids can cement soil particles together. Iron and aluminum hydroxides also are cementing agents. Fungi and actinomycetes hypha bind soil particles together. Plant roots help to form a stable structure. Bacteria are surrounded by a sticky gel binding soil particles together.

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 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. AGREGASI DAN PORI TANAH 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 = ∑ x i w i x i = mean diameter w i = dry mass fraction Diunduh 28/2/2012

41 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. STABILITAS AGREGAT Diunduh 28/2/2012

42 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. STABILITAS AGREGAT ….. Diunduh 10/3/2012 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.

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 (D b ) 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). 7FE10AB38F7F2E C ….. Diunduh 28/2/2012

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

45 PENGELOLAAN STRUKTUR TANAH ….. Diunduh 28/2/2012 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.

46 PEMBENTUKAN KERAK TANAH ….. Diunduh 28/2/2012 Following the rapid wetting and drying of an overworked seedbed, a solid sheet forms (0.2 to 5 centimetres thick) that is tight enough to prevent crop emergence. This is known as soil crusting. Best Management Practices 1.reduce secondary tillage; don't overwork the soil 2.use reduced tillage, no-till, or ridge tillage systems to leave crop residue on the soil surface 3.use a good crop rotation - include grasses and legumes where possible 4.use cover crops 5.use manure management to build soil organic matter 6.use timely tillage: work ground at suitable moisture level to prevent bringing up clods - more clods require more tillage 7.if a crust has formed before the crop emerges, rotary hoe to break up the crust - this will help the crop emerge, although this perpetuates soil structural problems 8.check plant populations: replant as a last resort 9.a light rain will help soften the crust.

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 1.crop growth can be slow, stunted, and variable, particularly under stressful weather conditions 2.root tips are flattened and/or swollen 3.roots below compacted layer grow normally 4.root growth is concentrated along face of soil clods 5.crop may exhibit various nutrient deficiencies 6.roots tend to grow sideways or down large- sized holes/cracks 7.roots aren't penetrating evenly into the soil. ….. 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 1.timely tillage and field operations - stay off wet fields; soil should be at proper moisture conditions at tillage depth 2.good drainage - tile drainage should be installed in fields with variable drainage 3.longer crop rotations that include forages/cereals 4.forage crops - leave in for longer than 1 year 5.tillage equipment - ensure it lifts and shatters soil (coulter chisel, cultivator) as opposed to pulverizing and grinding (disk) 6.alternate tillage depth so that tillage pans aren't created 7.limit the amount of traffic, including tillage, across a field 8.restrict compaction - create a long, narrow "footprint" with tire arrangement, e.g. radials, large tires, tracks limit axle loads to less than 5 tonnes/axle. ….. Diunduh 28/2/2012

49 STRUKTUR TANAH ….. Diunduh 28/2/2012 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.

50 AGREGAT TANAH ….. Diunduh 28/2/2012 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.

51 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. ….. Diunduh 28/2/2012

52 PEMBENTUKAN AGREGAT TANAH Diunduh 28/2/2012 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."

53 DEGRADASI AGREGAT TANAH Diunduh 28/2/2012 Some factors which destroy or degrade soil aggregates are: 1.excessive tillage 2.working the soil when it is too wet or too dry 3.use of anhydrous ammonia that speed decomposition of organic matter 4.excess nitrogen fertilization 5.allowing build up of excess sodium from salty irrigation water or sodium- containing fertilizers. Changes in percentage of macroaggregates and accumulation of whole-soil organic C with time since cultivation (modified from Jastrow, 1996).

54 AGREGASI PARTIKEL TANAH Diunduh 28/2/2012 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.

55 STABILITAS AGREGAT ….. Diunduh 28/2/2012 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).

56 EFEK VEGETASI TERHADAP STABILITAS AGREGAT ….. Diunduh 28/2/2012 The herbivorous nature of grazing animals clearly results in the removal of a portion of the vegetation. Removal of vegetation a&cts aggregate stability in several ways: 1.A decrease in cover reduces interception. Consequently, less kinetic energy is dissipated prior to striking the soil with the consequence that greater force per storm is applied to the soil tending to break aggregate bonds. 2.A decrease in above-ground biomass (standing crop and litter) results in less organic matter eventually being incorporated into the soil. As previously dis- cussed, organic matter is an important factor in aggregate formation and stability. 3.A decrease in above-ground biomass is eventually mirrored by a decrease in root biomass. Grass roots create a network physically binding soil particles together. Furthermore, grass roots induce aggregate formation by exuding biochemical byproducts which bind soil particles and distribute organic matter throughout the soil profile.

57 7FE10AB38F7F2E C 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. Diunduh 29/2/2012

58 ….. Diunduh 29/2/2012 What Are the Benefits of Organic Matter? Nutrient Supply Organic matter is a reservoir of nutrients that can be released to the soil. Each percent of organic matter in the soil releases 20 to 30 pounds of nitrogen, 4.5 to 6.6 pounds of P 2 O 5, and 2 to 3 pounds of sulfur per year. The nutrient release occurs predominantly in the spring and summer, so summer crops benefit more from organic-matter mineralization than winter crops. Water-Holding Capacity Organic matter behaves somewhat like a sponge, with the ability to absorb and hold up to 90 percent of its weight in water. A great advantage of the water-holding capacity of organic matter is that the matter will release most of the water that it absorbs to plants. In contrast, clay holds great quantities of water, but much of it is unavailable to plants. Soil Structure Aggregation Organic matter causes soil to clump and form soil aggregates, which improves soil structure. With better soil structure, permeability (infiltration of water through the soil) improves, in turn improving the soil's ability to take up and hold water. Erosion Prevention This property of organic matter is not widely known. Data used in the universal soil loss equation indicate that increasing soil organic matter from 1 to 3 percent can reduce erosion 20 to 33 percent because of increased water infiltration and stable soil aggregate formation caused by organic matter.

59 Organic matter and structure relation ….. Diunduh 29/2/2012 Relation between OC and 2-4 mm aggregates % for the two topographic positions.

60 Importance of Soil Bulk Density Diunduh 29/2/2012 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/cm 3 and 2.0 g/cm 3 ; root penetration is severely impacted at bulk densities greater than 1.6 g/cm 3. 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.

61 STRUKTUR TANAH Diunduh 29/2/2012 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.

62 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. Diunduh 29/2/2012

63 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. Diunduh 29/2/2012

64 Physical-Chemical Processes Positively charged ions such as calcium (Ca 2+ ), magnesium (Mg 2+ ) and aluminum (Al 3+ ), (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.smectite Diunduh 29/2/2012 The polyvalent cations (including Ca 2+, Fe 3+ and Al 3+ ) 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.

65 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. Diunduh 29/2/2012 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.

66 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 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. Diunduh 29/2/2012

67 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. Diunduh 29/2/2012 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.

68 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). Diunduh 29/2/2012 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?).

69 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. Diunduh 29/2/2012

70 . Structural class is the description of the size of the units. Verbal descriptions have size ranges as seen below. The size limits refer to the smallest dimension of any given structural unit, for example the width of a prism or the thickness of a plate. hapes of Structures Size Classes platy (mm) prismatic and columnar (mm) blocky (mm) granular (mm) Very fine<1<10<5<1 Fine Medium Coarse Very coarse>10>100>50>10

71 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 CO 2 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 (CH 4 ) and ethylene (C 2 H 4 ); if gaseous exchange between the atmosphere and the soil atmosphere occurs readily, favorable environments can be maintained. Diunduh 29/2/2012

72 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. Diunduh 29/2/2012 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.

73 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. Diunduh 29/2/2012

74 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. Diunduh 29/2/2012

75 EFEK PENGOLAHAN TANAH The amount and size of pores will decrease in this zone with concomitant air and water movement. With decreased rates of infiltration, surface runoff and soil erosion become issues. Plant roots have greater difficulty penetrating the platy structure and compacted soil, and limited rooting depth can affect plant survival. Irrigation, if not properly applied, can compound this problem by breaking up aggregates, increasing sodium content, and leaching clay. Diunduh 29/2/2012

76 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.porositysoil particlesorganic matterbond and aggregate Sumber: Diunduh 9/3/2012

77 SOIL STRUCTURE AND MACROPORES Sumber: Diunduh 9/3/2012 What it is: Sand, silt and clay particles are the primary mineral building blocks of soil. Soil structure is the combination or arrangement of primary soil particles into aggregates. Using aggregate size, shape and distinctness as the basis for classes, types and grades, respectively, soil structure describes the manner in which soil particles are aggregated. Soil structure affects water and air movement through soil, greatly influencing soil's ability to sustain life and perform other vital soil functions. Soil pores exist between and within aggregates and are occupied by water and air. Macropores are large soil pores, usually between aggregates, that are generally greater than 0.08 mm in diameter. Macropores drain freely by gravity and allow easy movement of water and air. They provide habitat for soil organisms and plant roots can grow into them. With diameters less than 0.08 mm, micropores are small soil pores usually found within structural aggregates. Suction is required to remove water from micropores.

78 BAHAN ORGANIK DAN AGREGAT TANAH Sumber: Diunduh 9/3/2012 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.

79 KERUSAKAN STRUKTUR TANAH Sumber: Diunduh 9/3/2012 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

80 AGREGASI Sumber: ….. Diunduh 9/3/2012 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.

81 Sumber: Diunduh 9/3/2012 Usually, microbial gums, polysaccharides and other secondary metabolites can bind soil particles together to form aggregates, somewhat like a lump of various particles. Spaces between aggregates are called inter-aggregate pores, and spaces within the aggregates intra-aggregate pores.

82 AGREGAT TANAH DAN AKAR TANAMAN Sumber: Diunduh 9/3/2012 Close-up view of a plant root. A)The mucigel layer containing some bacteria and clay particles on the outside of the root. Also shown is a mycorrhizal fungus sending out its rootlike hyphae into the soil. B) Soil aggregates surrounded by thin films of water. Plant roots take water and nutrients from these films. Also shown is a larger aggregate made up of smaller aggregates pressed together and held in place by the root and hyphae.

83 AGREGAT MAKRO Sumber: Diunduh 10/3/2012 Akar Tanaman dan Agregasi Tanah

84 Sumber: Diunduh 10/3/2012 PROSES AGREGASI TANAH

85 Sumber:….. Diunduh 10/3/2012 AGREGASI TANAH

86 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: Diunduh 10/3/2012

87 DISPERSI AGREGAT TANAH Dispersion is usually a problem of soil chemistry (namely, high levels of exchangeable sodium), although it can occur in non-sodic soils due to excessive mechanical disturbance of the soil. Slaking and dispersion can occur together. When this happens, both problems will have to be managed. Dispersion is the separation of the clay particles from the aggregates when the soil is wet (see Figure 4.1). Clay particles carry a negative electrical charge and tend to repel each other. Calcium, magnesium, sodium and potassium all carry positive charges and are attracted to the clay particles, forming a ‘bridge’, or bond, between the negatively charged clay particles. Calcium (Ca++) ions, followed by magnesium (Mg++) ions, are the strongest ‘bridge formers’ because they have two positive charges. Potassium (K+) and sodium (Na+) ions only have one positive charge, and their bonding of the clay particles is much weaker. If calcium is forming the bridge, the clay particles will hold together when they are wet. However, if sodium is forming the bridge, the bonding is much weaker and the clay particles tend to separate and repel one another when they are wet (in other words, they tend to disperse). Sumber: Diunduh 10/3/2012

88 DISPERSI AGREGAT TANAH Cloudy or muddy water in puddles is an indication that a soil may be dispersive. A continual stream of cloudy water running out of a mole drain outlet is also indicative of a dispersive clay-type soil. Mole drainage and open drains in dispersive soils may lead to severe soil erosion. When dispersion occurs, the dispersed clay particles fill up the pores between soil particles and aggregates; and when the soil dries out, the dispersed clay blocks up soil pores. This restricts seedling emergence, water and air movement, and root penetration. Dispersed soils are generally hardsetting and may form a surface crust. Dispersion with no slaking results in a ‘concrete-like’ lump being formed. Sumber: Diunduh 10/3/2012

89 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: Diunduh 10/3/2012

90 Sumber: Diunduh 10/3/2012 Soil Particle size Any soil will be composed of a variety of particle sizes ranging from large gravel particles down to tiny grains of clay.

91 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: Diunduh 10/3/2012

92 AGREGAT TANAH Sumber: ….. Diunduh 10/3/2012 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.

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