CIRI-CIRI FISIKA TANAH

CIRI-CIRI FISIKA TANAH

SUMBER: www.swac.umn.edu/classes/soil2125/.../l02b.ppt

Describes the proportion of soil particle sizes:SandSiltClay

Soil Texture influences other traits such as:Water Holding CapacityAeration


TEKSTUR TANAH

Smaller particles – larger internal surface area


EFEK UKURAN PARTIKEL TANAH

More pores – micropores

Larger pores – macropores


EFEK UKURAN PARTIKEL TANAH

SAND2.00 – 0.05 mm

SILT0.05 – 0.002 mm

CLAY< 0.002 mm


SEPARAT TANAH

Twelve TexturalClasses

Textural Triangle


KLASIFIKASI TEKSTUR TANAH

DENSITAS (KERAPATAN):

MASA per VOLUME

D = M V


DENSITAS & PERMEABILITAS TANAH

Dua macam kerapatan (densitas) dalam tanah:

Particle Density – PD : Bobot Jenis (BJ)

Bulk Density – BD: Bobot Isi (BI)



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



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


POROSITAS TANAH

Water Volume to Core Volume

wet weight (g) – dry weight (g)Porositas = ---------------------------------------- x 100% soil volume (cu cm)


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.


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%)


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%


POROSITAS TANAH

Pertanyaan:Which has greater porosity, Sand or Clay?Answer:Clay at about 50%; Sand is lower at about 30%

Why?


POROSITAS TANAH


TEKSTUR & PORI TANAH

• Why, then, does water move through sandy soil very rapidly, but moves slowly into clay ?



This is explained by the physical property Permeability



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


Fine-textured soils would be impermeable if not for:

Soil Structure


PERMEABILITAS

Structure – the way soil particles clump together into large units

called aggregates or

peds


STRUKTUR TANAH

Structure can alter the effects of texture- e.g. a fine-textured silty clay with good

structure can be permeable!


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


STRUKTUR TANAH

Two-step formation:1) Individual soil particles loosely aggregate2) Weak aggregates are cemented to

strengthen- clay- iron oxides- organic matter- microorganism gums


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


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


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


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)


CADAS TANAH

Temperatur TANAH (dipengaruhi oleh warna tanah, tekstur dan BOT)

Warna Tanah:Munsell soil color chart

Hue, Value, Chroma Misalnya: 10YR 3/6


TEMPERATUR TANAH

CIRI-CIRI FISIKA TANAH

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