CIRI-CIRI FISIKA TANAH
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Describes the proportion of soil particle sizes:SandSiltClay
Soil Texture influences other traits such as:Water Holding CapacityAeration
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TEKSTUR TANAH
Smaller particles – larger internal surface area
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EFEK UKURAN PARTIKEL TANAH
More pores – micropores
Larger pores – macropores
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EFEK UKURAN PARTIKEL TANAH
SAND2.00 – 0.05 mm
SILT0.05 – 0.002 mm
CLAY< 0.002 mm
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SEPARAT TANAH
Twelve Textural
Classes
Textural Triangle
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KLASIFIKASI TEKSTUR TANAH
DENSITAS (KERAPATAN):
MASA per VOLUME
D = M V
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DENSITAS & PERMEABILITAS TANAH
Dua macam kerapatan (densitas) dalam tanah:
Particle Density – PD : Bobot Jenis (BJ)
Bulk Density – BD: Bobot Isi (BI)
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DENSITAS & PERMEABILITAS TANAH
BJ rata-rata tanah ~ 2.65 g/cm3
BI average range from 1.0 – 1.8 g/cm3Depends on amount of pore space
BI = wt. dry soil = _g_ vol. dry soil cm3
e.g. BI = 650 g = 1.3 g/cm3 500 cm3
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DENSITAS & PERMEABILITAS TANAH
Usually expressed as a percentage; e.g. 50%
Two means determining porosity:1) Calculate ratio water volume to total core
volume2) Calculate from bulk density and particle
density
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POROSITAS TANAH
Water Volume to Core Volume
wet weight (g) – dry weight (g)Porositas = ---------------------------------------- x 100% soil volume (cu cm)
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POROSITAS TANAH
An oven-dry soil core, volume 500 cu cm, weighs 650g. When wet, it weighs 900g. Find it’s % porosity.
Porosity = 900g – 650g x 100% = 250g x100% = 50% 500 cu cm 500 cu cm
Note: the unit cancellation is made possible by the metric system which defines 1 cu cm of water as weighing 1g.
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POROSITAS TANAH
Bobot Isi (BI) vs. Bobot Jenis (BJDefines the percentage of the soil that is solid matterThe percent solid matter is subtracted from 100% to give percent porosity:
Porosity = 100% - (BI/BJ x 100%)
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POROSITAS TANAH
An undisturbed oven-dry soil, BD of 1.3 g/cu cm, consists of average mineral composition(PD 2.65 g/cu cm). Find its % Porosity:
Porosity = 100% - (1.3 g/cu cm/2.65 g/cu cm x 100%)
Porosity = 100% - (0.49 x 100%) = 100% - 49% = 51%
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POROSITAS TANAH
Pertanyaan:Which has greater porosity, Sand or Clay?Answer:Clay at about 50%; Sand is lower at about 30%
Why?
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POROSITAS TANAH
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TEKSTUR & PORI TANAH
• Why, then, does water move through sandy soil very rapidly, but moves slowly into clay ?
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TEKSTUR & PORI TANAH
This is explained by the physical property Permeability
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TEKSTUR & PORI TANAH
PERMEABILITAS
Permeability – the ease with which air, water, and roots move through soil
- Depends on number, size, and continuity of pores
- Liken to a maze
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Fine-textured soils would be impermeable if not for:
Soil Structure
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PERMEABILITAS
Structure – the way soil particles clump together into large units
called aggregates or
peds
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STRUKTUR TANAH
Structure can alter the effects of texture- e.g. a fine-textured silty clay with good
structure can be permeable!
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STRUKTUR TANAH
- Structure is classified by three groups of traits:1)Type – refers to shape of aggregates
e.g. Granular, Platy, Blocky, Prismatic, Columnar
2)Class – refers to size of pedse.g. very fine, fine, medium, coarse, very coarse
3)Grade – refers to strength and distinction of peds
e.g. weak/not visible vs. strong/easily distinguished
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STRUKTUR TANAH
Two-step formation:1) Individual soil particles loosely aggregate2) Weak aggregates are cemented to
strengthen- clay- iron oxides- organic matter- microorganism gums
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PEMBENTUKAN STRUKTUR TANAH
Soil Consistence – the behavior of soil when pressure is applied; measured at three different moisture levels: Wet, Moist, Dry (fig 4-15, p. 59)
Soil Tilth – ease of tillage, seedbed preparation, and seedling/root movement
Compaction – results from pressure applied at the soil surface
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KONSISTENSI TANAH
Pelumpuran, Bongkahan dan Kerak tanah:
Puddling occurs when pressure is applied to very wet soils (esp. plowing)
Crusts occur when bare soil is struck by raindrops; disperses soil then dries to a hardened crust
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PELUMPURAN TANAH
Memperbaiki sifat olah tanah:Best accomplished by improving structure- tilth relates to texture, structure, permeability, and consistence; however,
Tekstur dan Konsistensi sangat sulit diubah, sehingga perbaikan sifat olah tanah dilakukan dengan memperbaiki struktur dan menghindari pemadatan tanah
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SIFAT OLAH TANAH
Liang-liang tanah – continuous macropores leading from surface to deep subsoil
Cadas Tanah – any layer of hardened soil; includes:- claypans = cadas liat
- fragipans (clays) = cadas liat keras- plinthite (di daerah tropis)
- caliche (Ca cemented)
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CADAS TANAH
Temperatur TANAH (dipengaruhi oleh warna tanah, tekstur dan BOT)
Warna Tanah:Munsell soil color chart
Hue, Value, Chroma Misalnya: 10YR 3/6
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TEMPERATUR TANAH