ukuran partikel
DESCRIPTION
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 ,TRANSCRIPT
UKURAN PARTIKEL
Physical properties are influenced by particle sizeSize Classification (USDA):
Soil < 2 mmSand, 2 - 0.05 mm
Silt, 0.05 - 0.002 mmClay, <0.002 mm
• 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.
TEKSTUR TANAH
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.
Soil fraction Diameter Description
Gravel Larger than 2 mm
Coarse
Sand 0.05 - 2 mm Gritty
Silt 0.002 – 0.05 mm
Floury
Clay Smaller than 0.002 mm
Sticky when wet
• 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 chem rxns more than kaolinitic clays.
• 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.
• 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.
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.
SEGITIGA TEKSTUR TANAH
To determine soil texture by feel, us the 2 step method:
A. Take a handful of soil and moisten it to make a ball
B. Feel for clay (sticky, hard to squeeze, makes a ribbon). If there is a lot of clay, call it “clay”.
C. If there is some clay but it is softer than a dense clay, call it clay loam.
D. If it is very soft with just a little clay, call it “loam, and move to step 2 (next slide)
Step 1:
A. Next, modify the soil texture class from step 1 by feeling for sand (gritty, scratchy)
B. 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).
C. If there is NO sand, add the word “silty” to your original soil texture name (e.g. silty clay, silty clay loam)
D. If there is a little sand but not a lot, keep the original step 1 name, and you are done!
Step 2:
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!)
Kind of Particle
Diameter of Particle
# of Particles in 1 gram
Surface area of 1 gram
Sand 2 mm 90 11 cm2
Silt 0.02 mm 90,000,000(9x107)
1130 cm2
Clay 0.0002 mm 9x1013 113,000 cm2
SEGITIGA TEKSTUR TANAH
Liat = Clay
SiltSandLoamy Sand
Lempung berpasir = Sandy Loam
Sandy Clay Loam
Lempung Debu =
Silt Loam
Lempung = Loam
Lempung liat = Clay Loam
Silty ClayLoam
SiltyClay
Persen DebuPerse
n Liat
Persen Pasir
40
60
75
90
55
35
2010
SandyClay
70 50 20
Tanah berliat(tekstur halus)
Liat = Clay
Clay LoamSilty Clay
Loam
SiltyClay
40
60
55
SandyClay
Lempung liat berdebu
Liat berpasir
Tanah-tanah Berlempung / berdebu
(tekstur medium)
Silt
Sandy Clay Loam
Silt LoamLoam
Silty ClayLoam
60
75
90
35
20
70 50 20
Tanah-tanah berpasir(tekstur kasar)
Sand
Loamy Sand
Sandy Loam
20
10
70 50
Lempung berpasir
Pasir berlempung
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> pasirSebagai 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
UKURAN PARTIKEL & LUAS PERMUKAAN
• Luas permukaan (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
Klasifikasi ukuran PartikelSumber Soil Separates
Kerikil Pasir Debu Lempung
USDA > 2 mm 2 mm - 50 μm
50 μm - 2 μm
< 2 μm
ISSS > 2 mm 2 mm - 20 μm
20 μm - 2 μm
< 2 μm
USPRA > 2 mm 2 mm - 50 μm
50 μm - 5 μm
< 5 μm
BSI, MIT, DIN
> 2 mm 2 mm - 60 μm
60 μm - 2 μm
< 2 μm
• 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
UKURAN PARTIKEL & TEKSTUR TANAH
STRUKTUR TANAH: TIPE & UKURAN
Keterangan Struktur
Columnar & Prismatic
Subangular & Angular blocky
Granular
Sangat halus < 10 mm < 5 mm < 1 mm
Halus 10 – 20 mm 5 – 10 mm 1 – 2 mm
Sedang 20 – 50 mm 10 – 20 mm 2 – 5 mm
Kasar 50 – 100 mm 20 - 50 mm 5 – 10 mm
Sangat kasar > 100 mm > 50 mm > 10 mm
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).
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)
• 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
KONSISTENSI TANAH