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UKURAN PARTIKEL

UKURAN PARTIKEL. Physical properties are influenced by particle size Size Classification (USDA): Soil < 2 mm Sand , 2 - 0.05 mm Silt , 0.05 - 0.002 mm Clay , <0.002 mm . TEKSTUR TANAH. The way a soil “feels” is called the soil texture.

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UKURAN PARTIKEL

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  1. UKURAN PARTIKEL Physical properties are influenced by particle size Size Classification (USDA): Soil < 2 mm Sand, 2 - 0.05 mm Silt, 0.05 - 0.002 mm Clay, <0.002 mm

  2. TEKSTUR TANAH • The way a soil “feels” is called the soil texture. • Soil texture depends on the amount of each size of particle in the soil. • Sand, silt, and clay are names that describe the size of individual particles in the soil. • Sand are the largest particles and they feel “gritty.” • Silt are medium sized, and they feel soft, silky or “floury.” • Clay are the smallest sized particles, and they feel “sticky” and they are hard to squeeze. • There are 12 different soil texture classes depending on how much sand, silt, and clay is in each sample and we use the “Texture Triangle” to define these classes.

  3. FRAKSI TANAH • Soils consist of solid, liquid, gaseous and biotic components. • Sand and silt are merely broken down rock frags (consists of quartz, feldspar, mica, or other minerals). Chemically they are essentially inert compared with clay and organic matter, which are responsible for most of the chemical reactions in the soil.

  4. Clay particles are plastic and sticky when wet. They are highly adsorptive of water, gas, and dissolved substances. Clays are minute, plate-shaped, aluminosilicate crystals consisting of silicon, aluminum, iron, magnesium, oxygen, and hydrogen. • There are several types of clay. Two of the most important ones are kaolinite and smectite. Smectite clays have the ability to swell on wetting and shrink when dry. Smectite enter chemrxns more than kaolinitic clays.

  5. Clay is a negatively charged colloid. This negative charge is the reason that positively charged cations surround each clay particle. The individual cations can be exchanged for each other. • If the cations can get close to the surface of the clay, the neg charge on the clay is largely neutralized and the clay particles will cling together or flocculated. Calcium and magnesium are dominant in this area. They are small and effective in holding clay particles together.

  6. TEKSTUR TANAH • Texture – relative proportion of the various grain sizes in a soil. • To describe soil texture, names, such as loamy sand, silt loam, clay loam and silty clay are used. • The best soils are generally those which contain 10 to 20% clay, with silt and sand in approximately equal amounts, and a fair amount of organic matter.

  7. SEGITIGA TEKSTUR TANAH The content of sand, silt, and clay for the twelve main soil texture classes can be found on this triangle. Ex. Point A is in the sandy loam texture class with 65% sand, 25% silt, and 10% clay. Not that soils with relatively small clay contents (<40) are in the clay texture class bc the properties of clay readily predominate over the coarser fractions.

  8. To determine soil texture by feel, us the 2 step method: Step 1: • Take a handful of soil and moisten it to make a ball • Feel for clay (sticky, hard to squeeze, makes a ribbon). If there is a lot of clay, call it “clay”. • If there is some clay but it is softer than a dense clay, call it clay loam. • If it is very soft with just a little clay, call it “loam, and move to step 2 (next slide)

  9. Step 2: • Next, modify the soil texture class from step 1 by feeling for sand (gritty, scratchy) • If there is a lot of sand, add the word “sandy” to your original soil texture name from step 1 (e.g. sandy clay, or sandy clay loam). • If there is NO sand, add the word “silty” to your original soil texture name (e.g. silty clay, silty clay loam) • If there is a little sand but not a lot, keep the original step 1 name, and you are done!

  10. LUAS PERMUKAAN • In comparing clay with sand and silt, it is important to be aware of the relative amount of surface area of these particle size groups, bc it is on the surface that many chemical and physical processes take place. • Smaller = more surface area (clay is tiny!)

  11. SEGITIGA TEKSTUR TANAH Liat = Clay 40 PersenLiat 55 PersenDebu Silty Clay Sandy Clay 60 35 Silty Clay Loam Lempungliat = Clay Loam Sandy Clay Loam 75 20 Lempung = Loam Lempungberpasir = Sandy Loam LempungDebu = Silt Loam 90 10 Loamy Sand Silt Sand 50 70 20 PersenPasir

  12. 40 Liat = Clay 55 Silty Clay Sandy Clay 60 Silty Clay Loam Clay Loam Tanah berliat (teksturhalus) Liatberpasir Lempungliatberdebu

  13. 60 35 Silty Clay Loam Sandy Clay Loam 75 20 Loam Silt Loam 90 Silt 50 70 20 Tanah-tanahBerlempung / berdebu (tekstur medium)

  14. 20 Sandy Loam 10 Loamy Sand Sand 50 70 Tanah-tanahberpasir (teksturkasar) Lempungberpasir Pasirberlempung

  15. TEKSTUR TANAH • Sifat kimia, fisika dan mineralogi partikel tanah tergantung pada ukuran partikelnya. • Semakin kecil ukuran partikel maka luas permukaannya semakin besar. Jadi luas permukaan fraksi lempung > fraksi debu> pasir Sebagai contoh : • Partikel bentuk bola dengan berat 1 gr dengan bulk density 2,65 g/cm3 dipecah menjadi 106 partikel yang lebih kecil berbentuk bola dengan berat masing-masing partikel 10-6 g. • Maka :Luas permukaan untuk partikel dengan berat 1 gr adalah sbb : • Volume = (1g)/(2,65 g/cm3) = 0,377 cm3 • Volume bola = 4/3 . 3,14. r3 sehingga r3 = (0,377 x 3) /4 . 3,14 = 0,0901 • Radius = r = 0,448 cm = 4,48 x 10-3 m

  16. UKURAN PARTIKEL & LUAS PERMUKAAN • Luaspermukaan (surface area/SA) = 4 . 3,14 . r2 = 2,52x10-4 m2 • Setelah dipecah menjadi partikel yang lebih kecil \; • Volume = (10-6)/(2,65 g/cm3) = 3,77 x 10-7 cm3 • r3 = 3,77 x 10-7 cm3 x 3 = 9,01 x 10-8 cm 3,14 • r = 4,48 x 10-5 m • SA dari masing-masing partikel kecil = 4.3,14 r2 • = 4x 3,14 x (4,48x10-5 m)2 = 2,52 x 10-8 m2/partikel • Kolektif SA= 2,52 x 10-8 m2/partikel x 106 = 2,52 x 10-2 m2 Dengan kata lain, • Pemecahan partikel seberta 1 gr menjadi 106 partikel kecil dapat meningkatkan luas permukaan 100 kali lipat dari 2,52 x 10-4 m2 menjadi 2,52 x 10-2 m2

  17. Klasifikasi ukuran Partikel

  18. UKURAN PARTIKEL & TEKSTUR TANAH • Tekstur tanah diartikan sebagai proporsi pasir, debu dan lempung • Partikel ukuran lebih dari 2 mm, bahan organik dan agen perekat seperti kalsium karbonate harus dihilangkan sebelum menentukan tekstur • Tanah bertekstur sama misal geluh berdebu mempunyai sifat fisika dan kimia yang hampir sama dengan syarat mineralogi lempung. • Tekstur tanah ditentukan di lapangan dengan cara melihat gejala konsistensi dan rasa perabaan menurut bagan alir dan di laboratorium dengan metode pipet atau metode hidrometer • Tekstur tanah menentukan tata air, tata udara, kemudahan pengolahan dan struktur tanah

  19. STRUKTUR TANAH: TIPE & UKURAN

  20. STRUKTUR / AGREGAT TANAH • Merupakan gumpalan tanah yang berasal dari partikel-partikel tanah yang saling merekat satu sama lain karena adanya perekat misalnya eksudat akar, hifa jamur, lempung, humus, dll. • Ikatan partikel tanah berwujud sebagai agregat tanah yang membentuk dirinya • Pengamatan struktur tanah di lapangan (SSS, 1975) terdiri dari : • 1. Pengamatan bentuk dan susunan agregat tanah tipe struktur (lempeng, tiang, gumpal, remah, granuler, butir tunggal, pejal) • 2. Besarnya agregat klas struktur (sangat halus, halus, sedang, kasar, sangat kasar) • 3. Kuat lemahnya bentuk agregat derajad struktur (tidak beragregat, lemah, sedang, kuat).

  21. KONSISTENSI TANAH • Adalah derajad kohesi dan adhesi antara partikel-partikel tanah dan ketahanan massa tanah terhadap perubahan bentuk oleh tekanan dan berbagai kekuatan yang mempengaruhi bentuk tanah. • Konsistensi ditentukan oleh tekstur tanah dan struktur tanah. • Cara penentuan (1) lapangan : memijit tanah dalam kondisi kering, lembab dan basah (2) laboratorium : angka-angka Atterberg • Penentuan di lapangan ; • Kondisi kering : kekerasan (lepas, lunak, keras) • Kondisi lembab : keteguhan (lepas, gembur, teguh) • Kondisi basah : kelekatan dan plastisitas • Penentuan di laboratorium : menentukan Batas Cair (BC), Batas Lekat (BL), Batas gulung (BG) dan Batas Berubah Warna (BBW)

  22. KONSISTENSI TANAH • Batas Cair : Kadar air yang dapat ditahan oleh tanah • Batas Lekat : Kadar air dimana tanah tidak melekat ke logam • Batas Berubah Warna adalah batas air dimana air sudah tidak dapat diserap oleh akar tanaman karena terikat oleh tanah • Jangka Olah (JO) : kadar air dimana tanah mudah diolah (BL-BG) • Derajad keteguhan (DT) : BC-BG • Surplus positif : Bl > BC artinya tanah mudah merembeskan air; • Surplus negatif : BL<BC : tanah sukar merembeskan air

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