SIFAT-SIFAT FISIK TANAH 1
Batas Horison • Bentuk topografi batas horison : rata, berombak, tidak teratur, terputus
A
B
C
rata
berombak
tidak teratur
terputus
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
BENTUK Ketebalan :
1-10 mm
S T R U K T U R
1mm-10 mm
5 mm50 mm
10 – 100 mm
Granular Columnar
Blocky Single Grained
Prismatic 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
Types of structure: Structureless 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.
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
