SIFAT-SIFAT FISIK TANAH 1

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Batas Horison

• Bentuk topografi batas horison : rata, berombak,

tidak teratur, terputus

rata

berombak

tidak teratur

terputus

A

B

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Ketajaman peralihan

Nyata (lebar peralihan< 2,5 cm), jelas (2,5-6,5 cm), berangsur

(6,5-12,5 cm), baur (> 12,5 cm)

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WARNA

• Sifat fisik yang mudah dilihat

• _{Terjadi karena pengaruh berbagai faktor}

• Tanah : merah, cokelat, abu-abu, kuning dan hitam.

• _{Kebiru-biruan + kehijau-hijauan terjadi kemudian}

• Warna tidak dominan : campuran warna abu + warna

karat

• Becak-becak (motling) : ≥ 2 warna pada satu bidang

permukaan.

• Produktivitas :

• Hitam > coklat>coklat seperti karat>abu

coklat>merah>abu-abu>kuning>putih

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INFORMASI DARI WARNA TANAH

• Tingkat pelapukan : merah



pelapukan

lanjut.

• Bahan organik : gelap



BO tinggi

• Drainase :

–

Baik



merah atau kuning coklat

–

Buruk



kelabu kebiruan + bercak.

• Horison pencucian



putih /pucat.

• Horison pengendapan



merah gelap

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Munsell Colour Chart

• HUE

(Warna utama tanah)

–

Merah (R), Kuning (Y), Hijau (G), coklat(B)

• VALUE

(derajat terangnya warna)

–

0- 8 , semakin tinggi warna makin terang(makin

banyak sinar dipantulkan)

• CHROMA

( kekuatan/intensitas warna)

–

0-8 , semakin tinggi kekuatan meningkat

7,5 YR 5/4

• Hue : 7,5 YR, value = 5, chroma=4



coklat

• Catat keadaan tanah : basah, lembab, kering.

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TEKSTUR

• _{Perbandingan kandungan partikel-partikel}

tanah primer berupa fraksi liat, debu, dan

pasir dalam suatu masa tanah.

• Kualitatif : kekasaran/kehalusan tanah

• Kuantitatif : persentase tiap fraksi tanah

–

Pasir : 50 µ - 2 mm

–

Debu : 2 µ - 50 µ

–

Liat : < 2 µ

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Soil particles



Sand:

Particles range in size from

very fine (0.05 mm) to very coarse (2.0 mm) in average diameter.

Most particles can be seen

without a magnifying glass.

Feel coarse and gritty when

rubbed between the thumb and fingers, except for mica flakes.

Sand texture

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Soil particles



Silt:

Particles range in size from

0.05 mm to 0.002 mm.

Cannot usually be seen by

the unaided eye

When moistened, silt feels

smooth but is not slick or sticky. When dry, it is

smooth and floury

Silt loam texture

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Soil particles



Clay

:

Particles are finer than 0.002

mm.

Can be seen only with the

aid of an electron microscope.

Feels extremely smooth or

powdery when dry, and

becomes plastic and sticky when wet.

Clay texture

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Cara Penentuan

• Memijit tanah basah diantara jari-jari

PASIR

Rasa kasar

Butiran pasir di telapak tangan

DEBU

Rasa licin

LIAT

Lengket

Membentuk bola

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TANAH BERAT VS TANAH RINGAN

TANAH BERAT

Kandungan liat tinggi

Menyimpan air banyak

Plastis

Lengket

Sukar diolah

Bulk density tinggi

TANAH RINGAN

Kandungan pasir tinggi

Infiltrasi tinggi

Mudah lepas

Mudah diolah

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Light Soils vs Heavy Soils



Light Soils

- sandy or coarse texture



Heavy

Soils

- clay or fine texture



Loamy

Soils

- medium textured



more desirable characteristics usually

associated with highly productive soils that are

easier to manage

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STRUKTUR TANAH

• Susunan butir-butir primer dan agregat-agregat

primer tanah secara alami menjadi bentuk

tertentu yang dibatasi oleh bidang-bidang yang

disebut agregat.

• “Bentuk struktur tanah”

• Gumpalan kecil dari butir-butir tanah

• Terjadi karena butir-butir pasir, debu, dan liat

terikat satu sama lain oleh perekat (koloid liat dan

humus)

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S

T

R

U

K

T

U

R

BENTUK Ketebalan : 1-10 mm 1mm-10 mm 5 mm- 50 mm 10 – 100 mm

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Granular

Blocky

Prismatic

Columnar Single Grained Massive

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Types of structure: Granular and Blocky



Granular:

Soil particles are arranged in small, rounded units.

Common in surface soils (A horizons).

Most distinct in soils with relatively high organic matter content.

Resembles cookie crumbs and is usually less than 0.5 cm in diameter

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Types of structure: Granular and Blocky



Blocky:

Soil particles are arranged to form block-like units, which are about as wide as they are high or long.

Some blocky peds are rounded on the edges and corners; others are angular.

Blocky structure is commonly found in the subsoil, although some eroded fine-textured soils have blocky structure in the surface

horizons.

Blocky

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Blocky Structure

• Irregular blocks that are

usually 1.5 - 5.0 cm in

diameter.

• Can be subangular or

angular blocky.

http://soil.gsfc.nasa.gov/ pvg/blocky.gif

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Types of structure: Platy



Platy:

Soil particles are arranged in plate-like sheets, which are

approximately horizontal in the soil and may occur in either the surface or subsoil, although they are most common in the subsoil.

Platy structure strongly limits downward movement of water, air, roots and may result from compaction.

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Platy Structure

• Thin, flat plates of soil

that lie horizontally.

• Usually found in

compacted soil.

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Types of structure: Prismatic



Prismatic:

Soil particles are arranged into large peds with a long vertical axis.

Well developed subsoil prisms are

associated with fragipans (dense subsoil layers), or soils that swell when wet and shrink when dry, reducing air and water movement.

Most clayey subsoils exhibit prismatic macro-structures to some extent.

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Prismatic Structure

• Vertical columns of soil

that might be a number

of cm long.

• Usually found in lower

horizons.

http://soil.gsfc.nasa.gov/

pvg/prismatic.gif http://soils.usda.gov/technical/man ual/images/fig3-27_large.jpg

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Columnar Structure

• Vertical columns of soil that have a salt "cap" at the top.

• Found in soils of arid climates.

http://soil.gsfc.nasa.gov /pvg/columnar.gif

http://soils.usda.gov/technical/manual /images/fig3-28_large.jpg

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

Structureless:

Two types:

•Massive: no definite structure or shape, as in some C horizons or compacted material.

•Single grain: typically

individual sand grains in A or C horizons not held together by organic matter or clay.

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Massive Structure

• Soil has no visible structure, is hard to break apart

and appears in very large clods.

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Single-grained Structure

• Soil is broken into individual particles that do not

stick together.

• Always accompanies a loose consistence.

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Four Main Types of Soil Structure



Platy

- thin horizontal sheets overlapping

each other



Prismatic

- long vertical columns without

rounded tops



Block-like

- irregular shaped cubes



Spheroidal

- rounded and often referred

to as granular or crumb; usually found in

the topsoil

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Two Types of Structureless Soils



Single grained soils like sand



Solid massive condition with no noticeable

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Figure 3. The size of pore spaces between soil particles plays a key role in plant growth. Pore spaces are a function of soil texture and

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• Comparative pore space: Left: soil with large pore space. Right: Compacted soil lacking large pore space

.

Pore space is a function of soil texture, structure and the activity of beneficial soil organisms. Water coats the solid particles and fills the smaller pore

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• Comparative movement of water in sandy and clayey soils. In sandy soils, water readily moves downward due to the force of gravity. In clayey soils, water slowly moves out in all direction by capillary action.

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• On landscape soils with a texture interface in the soil profile, too frequent of irrigation

creates a perched water table above the interface line. Roots below the perched water table have low soil oxygen levels

.

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Shapes of Structures

Size Classes platy

(mm) prismatic and columnar (mm) blocky (mm) granular (mm) Very fine <1 <10 <5 <1 Fine 1 - 2 10 - 20 5 - 10 1 - 2 Medium 2 - 5 20 - 50 10 - 20 2 - 5 Coarse 5 - 10 50 - 100 20 - 50 5 - 10 Very coarse >10 >100 >50 >10