sifat-sifat fisik tanah · 2015-06-01 · warna •sifat fisik yang mudah dilihat •terjadi karena...

SIFAT-SIFAT FISIK TANAH 1

Batas Horison • Bentuk topografi batas horison : rata, berombak,

tidak teratur, terputus

rata berombak tidak teratur terputus

A

B

C

Ketajaman peralihan

Nyata (lebar peralihan< 2,5 cm), jelas (2,5-6,5 cm), berangsur (6,5-12,5 cm), baur (> 12,5 cm)

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

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 pengendapanmerah gelap

• Warna gelap evaporasi tinggi cepat kering..

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.

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

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 (Photo by Jim Baker, Virginia Tech)

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 (photo by Jim Baker, Virginia Tech)

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 (Photo by Jim Baker, Virginia Tech)

Cara Penentuan

• Memijit tanah basah diantara jari-jari

PASIR Rasa kasar Butiran pasir di telapak tangan

DEBU Rasa licin

LIAT Lengket Membentuk bola Dibentuk benang tidak patah

Segi Tiga Tekstur

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 Bulk density rendah

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

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)

• Bentuk, ukuran, ketahanan berbeda-beda

S T R U K T U R

BENTUK Ketebalan :

1-10 mm 1mm-10 mm 5 mm- 50 mm 10 – 100 mm

Granular Blocky Prismatic Columnar Single Grained Massive

Platy

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

Jim Baker, Virginia Tech

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

W. Lee Daniels, Virginia Tech

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

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.

Jim Baker, Virginia Tech

Platy Structure

• Thin, flat plates of soil that lie horizontally.

• Usually found in compacted soil.

http://soil.gsfc.nasa.gov/pvg/platy.gif http://soils.ag.uidaho.edu/soilorders/i/Arid_03.jpg

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.

Jim Baker, Virginia Tech

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

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

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.

Types of structure: Structureless

Massive Structure

• Soil has no visible structure, is hard to break apart and appears in very large clods.

http://soil.gsfc.nasa.gov/pvg/massive.gif http://soils.usda.gov/technical/manual/images/fig3-31_large.jpg

Single-grained Structure

• Soil is broken into individual particles that do not stick together.

• Always accompanies a loose consistence.

• Commonly found in sandy soils.

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

Two Types of Structureless Soils

Single grained soils like sand

Solid massive condition with no noticeable peds

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 structure.

• 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 spaces. Air fills the larger pore spaces.

• 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.

• 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.

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

Structured Soil

more desirable because it:

is easier to cultivate

allows more water intake

does not restrict root growth

encourages better drainage within pore spaces

allows entry of oxygen into the pore spaces after the water has drained

facilitates organic matter decomposition and the release of plant nutrients

Destruction of Soil Structure

Soil structure can be destroyed by:

working the soil when it is wet

repeated movement of equipment or livestock

repeated use of equipment at the same depth in the soil

continual flooding of the soil

Improving Soil Structure

Leaving it alone, in time it will repair itself

Planting a green manure crop

Incorporating plant residue into the soil

Kemantapan/Ketahanan

1. Tingkat perkembangan lemah (butir-butir tanah mudah hancur)

2. Tingkat perkembangan sedang (butir-butir tanah agak sukar hancur)

3. Tingkat perkembangan kuat (butir-butir tanah mudah sukar hancur)

Tanah tidak berstruktur

butir- butir tanah tidak melekat satu sama lain

Tanah pasir

Tanah berstruktur masiv/pejal

butir- butir tanah melekat satu sama lain menjadi satu satuan yang kompak

Tanah berstuktur baik

Granular - tidak saling bersinggungan

- pori

- tata udara baik