BAHAN KAJIANMK. DASAR ILMU TANAH

SIFAT FISIKA TANAH

Dihimpun olehSoemarno

Jurusan Tanah FP UB Februari 2012

TEKSTUR TANAH

Efek Ukuran partikel tanah

… Diunduh 15/2/2012

Tipe-Tipe Struktur TanahTipe-Tipe Struktur Tanah

Common to Ohio soils just below Ap

(> 8”)

Plow layer

Sand

Deeper in profile (>3-4’)

Granular

Platy

Prismatic

Columnar

Blocky

Single Grain

Massive

TEKSTUR TANAH• Luas permukaan internal

• Pori tanah

Relative proportion of the various size separates in a soil.

Important because it affects and is related to several soil properties such as soil structure, aeration, water holding capacity, nutrient storage, water movement,

and bearing strength.

Fraksi Tanah = Soil Separates

Mineral soil is considered as a porous mixture of inorganic particles, decaying organic matter, water

and air.

Particle size and particle size distribution of these inorganic particles have an important bearing on

the physical properties of soil.

TEKSTUR TANAH

TEKSTUR TANAH

Soil separates do not act as individuals, but as partners, or aggregates. Aggregates are the clumps of soil separates.

When aggregates are bound together into large masses they are called peds

It is difficult to alter the soil texture on the field level.

TEKSTUR TANAH

Mineral fraction of soil is divided into are called soil separates. three major size groups. These groups

Sand - 0.05 mm to 2 mm in diameterSilt - 0.002 mm to 0.05 mm in diameterClay - <0.002 mmGravel - 2 mm to 2 cmStones - >2 cm

Particles of <0.001 mm are designated as colloids - clay, a colloid is unique because of its large surface area.

• Klasifikasi tekstur tanah• Penentuan tekstur tanah

TEKSTUR TANAH

• Karakteristik kelas tekstur• Modifiksi tekstur tanah

TEKSTUR TANAH

“Big” smaller really small

Sand silt clay

Perbandingan ukuran partikel tanah

• Surface area per unit volume– 1 g sand ~ 0.1 m2

– 1 g silt ~ 1 m2

– 1 g clay ~ 10-1000 m2

•

•

lowest

highest

Large surface area means more charge so greater ability to hold water and nutrients

Coarse textured soils have larger pores, fine textured soils have greater total pore space

Gee whiz fact:

Fine clay has ~10,000 times as

much surface area as the same

wt. med. grain sand

h Surface area h weathering

TEKSTUR TANAH

Surface area, pore volume, nutrient supply capacity, plasticity and cohesion,

swelling

Particle SizeParticle Size

ClayClay SiltSilt SandSand

Particle SizeParticle Size

ClayClay SiltSilt SandSand

Pore size, infiltration rate, drainage rate, aeration

Siklus Hidrologi dan TanahSiklus Hidrologi dan Tanah

Color

Structure

Bulk Density

Texture

pH

Temperature

Moisture

HorizonDepths

Sifat tanah yang menjadi bagian dari siklus hidrologi.

PENGARUH TEKSTUR

Pasir Debu Liat

Water-holding capacity

Aeration

Drainage

Nutrient retention

Low Medium High

Good PoorMedium

Slow Very slowFast

HighLow Medium

DENSITAS DAN PERMEABILITAS TANAH

• Kerapatan partikel = Particle density

• Bobot Isi Tanah• Porositas Tanah

DENSITAS DAN PERMEABILITAS TANAH

Permeabilitas tanah ditetapkan dalam keadaan jenuh pada contoh tanah yang tidak terganggu yang dirumuskan :

K = (QL) / t.h.A.

Dimana : K = Permeabilitas ( cm/jam ) Q = Banyaknya air setiap pengukuran ( cm3 ) L = Tebal contoh tanah ( cm ); H = Tinggi permukaan air dari permukaan tanah ( cm2 ) A = Luas permukaan contoh tanah ( cm2 ) t = Waktu ( jam )

Permeability

DENSITAS DAN PERMEABILITAS TANAH

BOBOT ISI – BULK DENSITY

• Calculate soil bulk density and % pore space

• Discuss factors influencing the above soil properties

• Identify the difference between texture and structure

Bobot isi tanah merupakan kerapatan tanah per satuan volume yang dinyatakan dalam dua batasan

berikut ini:

(1)Kerapatan partikel (bobot partikel = BP) adalah bobot massa partikel padat per satuan volume tanah, biasanya tanah mempunyai kerapatan

partikel 2,6 gram cm-3, dan

(2) Kerapatan massa (bobot isi = BI) adalah bobot massa tanah kondisi lapangan yang dikering-

ovenkan per satuan volume.

http://dasar2ilmutanah.blogspot.com/2009/04/sifat-fisika-tanah-bagian-3-bobot-isi.html

..... Diunduh 16/2/2012

• Density

• Porosity–

particle density: mass per unit volume (not pore space)

bulk density: mass per unit volume (including pore space)

the volume percentage (%) of the total bulk

soil NOT occupied by

solids

~ 2.65 Mg/m3 (Dp of quartz mineral, dominant mineral in most soils)

ranges 0.1 – 2.65 Mg/m3

BOBOT ISI – BULK DENSITY

• O.M. decreases bulk density• Compaction increases bulk

density• Increased bulk density

lowers water infiltration and restricts root growth

Por

e vo

lum

e

Particle SizeClayClay SiltSilt SandSand

Mass of dry soil per unit bulk volume, INCLUDING pore space

Bulk density is relatively high in coarse-textured

soils because total pore volume is low

BOBOT ISI – BULK DENSITY

• Histosols (0.1-0.7 Mg/m3)

• Cultivated clay and silt loams (0.9-1.5 Mg/m3)

• Cultivated sandy loams and sands (1.2-1.8 Mg/m3)

• Concrete (ca. 2.4 Mg/m3)

• Quartz mineral (2.65 Mg/m3)

LOW

HIGH

BOBOT ISI – BULK DENSITY

• OM: ~0.5 Mg/m3

• “normal” soils: Db ~ 1.2 - 1.8 Mg/m3

– Clayey soils lower than sandy soils

• Upper limit: ~2.65 Mg/m3

BOBOT ISI – BULK DENSITY

Kerapatan massa lapisan yang bertekstur halus biasanya antara 1,0-1,3 g/cm3. Jika struktur tanah kasar maka kerapatan massa 1,3-1,8

g/cm3.

Semakin padat suatu tanah makin tinggi kerapatan massa atau bulk densitynya sehingga makin sulit meneruskan air atau ditembus oleh

akar tanaman.

http://repository.usu.ac.id/bitstream/123456789/16232/4/Chapter%20II.pdf

....... Diunduh 15/2/2012

Effect varies with soil texture!

Depth

Bulk density

Forest

Clear cut

????

Depth

Bulk density

Forest

Clear cut

????

BOBOT ISI – BULK DENSITY

Soil bulk density on skid trails: does tillage help??

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

control untilled tilled

Bul

k de

nsity

(g/c

m^3

)

Texture Yrs cropped

Increase in Db due to texture and

cultivation

Loam 58

Silt loam 40

Clay 70

In general, the finer the texture, the more it compacts if aggregates are destroyed

Coarse

Fine

0.18

0.26

0.30

BOBOT ISI – BULK DENSITY

BOBOT ISI – BULK DENSITY

STRUKTUR TANAH

Tanah tidak berstruktur

• Tipe-tipe struktur tanah• Pembentuka struktur tanah

STRUKTUR TANAH

Agregasi tanah merupakan proses-proses dimana partikel tanah utama (pasir, debu, liat) terikat

bersama-sama oleh gaya alami dan bahan-bahan yang dihasilkan oleh eksudat akar dan aktifitas

mikrobia.

Agregat Suatu unit struktur tanah yang terbentuk oleh proses alami yang berlawanan dengan proses

buatan, dan biasanya berdiameter <10 mm.

Agregat yang stabil air adalah suatu agregat yang stabil dengan gaya-gaya yang diakibatkan oleh air

seperti titik hujan, atau agitasi dalam analisa saringan basah.

• Structure–

• Aggregate stability–

spatial arrangement of primary soil particles

how easily or not do the peds fall apart?

Low bulk density Lots of macroporesStable aggregates

Goal of good soil mgmt.

STRUKTUR TANAH

• The arrangement of primary soil particles into groupings called aggregates or peds

• Binding agents provided by plant roots (exudates), organic matter (OM), and clays

• Most important contributor to good structure is OM

STRUKTUR TANAH

Perbedaan antara Tekstur dan struktur

• Texture = proportions of different particle sizes (% sand, silt, clay)

• Structure = spatial arrangement of those particles

STRUKTUR TANAH

Agregasi tanah dihasilkan dari penyusunan partikel, flokulasi, dan sementasi yang diperantarai oleh bahan

organik tanah, biota tanah, jembatan ionik, liat, dan karbonat.

Struktur tanah yang baik memiliki kemantapan agregat yang diperlukan untuk meningkatkan ketersediaan hara

bagi tanaman, produktivitas tanaman, porositas, dan menurunkan tingkat erosi.

Konsep dasar dari agregasi adalah pembentukan partikel sekunder melalui penggabungan partikel mineral dengan

bahan organik dan anorganik. Dinamika agregasi sangat kompleks dan dipengaruhi oleh interaksi beberapa faktor seperti lingkungan, pengelolaan tanah, tanaman, komposisi mineral, tekstur, konsentrasi

karbon organik tanah, proses pedogenesis, aktivitas mikroorganisme tanah, ion-ion yang dapat dipertukarkan,

cadangan nutrisi di dalam tanah, dan kelembaban

Particles bind because organic compounds and some minerals are “sticky”

– Biological sources: polysaccharides, proteins, bacterial “glues”

– Mineralogical sources : oxides, carbonates, silicates (clay particles)

STRUKTUR TANAH

KARAKTERISASI STRUKTUR

• Type:– Four (4) principal shapes

• Granular (A), platy (E), blocky (B), prismatic (B)

• Size– fine, medium, coarse

• Grade:– Strong, moderate, or weak

• In general, – if lots of clay STRONG structure,

bigger blocks – If lots of OM granular structure

Shape of the aggregates

distinctness (how obvious)

TIPE STRUKTUR: Spheroidal

Structure type: Platey

Structure type: Blocky

Structure type: Prism-like

Sodium induced – disperses clays

C

B

E

A Granular

Platy

Blocky

Massive

TELADAN LABEL STRUKTUR TANAH

GRADE SIZE TYPE

• Moderate coarse subangular blocky

• Weak medium platy

• Strong very coarse prismatic

• Moderate very fine granular

AGREGAT ADALAH UNIT STRUKTUR

• Amount of OM• Type and amount of clay • Amount of stabilizing/flocculating

minerals (calcium carbonate, gypsum, etc.)

The same things that lead to strong structure make stable

aggregates!

AGREGAT

Aggregates contain many small pores; area between aggregates large pores

Total ruang pori dapat dihitung dengan menggunakan data bobot jenis partikel – partikel dan bobot isi tanah sebagai berikut:

TRP = 1 - BD/PD . 100%

Dimana: TRP = Total Ruang Pori ‘ BD = Bulk Density (g/cm3) ; PD = Partikel Density

MENGAPA AGREGAT TANAH SANGAT PENTING?

Increase porosity

Increase water infiltration, drainage, decrease runoff

Increase water holding capacity

Ruang pori tanah ialah bagian yang diduduki udara dan air.

Jumlah ruang pori sebagian ditentukan oleh susunan butir-butir padat, apabila letak keduannya cenderung erat, seperti pada

pasir atau subsoil yang padat, total porositasnya rendah.

Sedangkan agregat bergumpal seperti yang kerap kali terjadi pada tanah-tanah yang bertekstur sedang yang besar kandungan

bahan organiknya, ruang pori persatuan volume akan tinggi.

KONDISI YANG MEMPERBAIKI STABILITAS AGREGAT

1. Low disturbance

2. High root abundance

3. High fungal biomass

4. High OM

5. High clay content

Pembentukan agregat terjadi melalui beberapa cara dan dikelompokkan dalam tingkat ukuran

yaitu makroagregat (> 250 μm) dan mikroagregat (< 250 μm).

Teori agregasi yang dikemukakan Tisdall (1996) adalah mikroagregat (< 250 μm) dibentuk oleh

molekul organik (MO) yang menempel pada liat (L) dan kation polivalen (P) membentuk partikel (L-P-MO), yang saling berikatan dengan partikel (L-P-

MO) lainnya membentuk makroagregat [(L-P-MO)x]y.

EFEK BOT TERHADAP STABILITAS AGREGAT

Mekanisme agregasi melalui proses flokulasi dan fragmentasi. Flokulasi terjadi jika partikel tanah yang pada awalnya dalam keadaan terdispersi, kemudian

bergabung membentuk agregat. Sedangkan fragmentasi terjadi jika tanah dalam keadaan masif, kemudian terpecah-pecah membentuk agregat yang

lebih kecil. Semakin mantap suatu agregat tanah, semakin rendah

kepekaannya terhadap erosi (erodibilitas tanah).

Efek akar dan pengolahan tanah terhadap stabilitas agregat

Kemantapan agregat tanah dipengaruhi oleh :

(i)jumlah dan jenis bahan organik di dalam tanah, khususnya lem dan musilage, (ii) keberadaan bakteri dan fungi serta akar tanaman berukuran mikro, (iii)

pembasahan dan pengeringan, (iv) freezing dan thawing, (v) situs pertukaran kation alami, dan (vi)

aktivitas biota tanah khususnya cacing tanah.

Cara memperbaiki struktur tanah

• Reduce disturbance• Work soil when dry• Mulch soil surface• Add organic materials (crop residues, compost,

manure)• Use cover crops

http://www.seafriends.org.nz/enviro/soil/ecology.htm diunduh 15/2/2012

Wet soil Moist soil Dry soil

KONSISTENSI TANAH

Soil consistency states for a sand and a clay soil (friable soil is best for tillage).

• Compaction• Aggregate destruction• Puddling and clods• Surface crusts• Improving tilth• Soil channels

SIFAT OLAH TANAH

Kemantapan agregat tanah dapat didefinisikan sebagai kemampuan tanah untuk bertahan terhadap gaya-gaya yang

akan merusak.

Gaya-gaya tersebut dapat berupa kikisan angin, pukulan hujan, daya urai air

pengairan, dan beban pengolahan tanah.

PEMADATAN TANAH DAN PERTUMBUHAN TANAMAN

• Silt loam in Arkansas:

decreasing Db by 16% increased cotton yields 13% during a normal year59% during a dry year

• Medium textured soils in Washington

Db > 1.2 Mg/m3; positively correlated with diseases in peas and beans

(h pore space= h water storage capacity)

EFEK PEMADATAN TANAH

Increasing soil compactiong(increasing bulk density)

KERAPATAN PARTIKEL = Particle Density

• Mass of dry soil per unit volume of solids, this EXCLUDES pore space

• So if you compact a soil, does particle density change??

No!

Comparison of bulk and particle density

g/cm3 = Mg/m3

1.32g 1.32

g

Soil Pans• Lapisan tanah yang diperkeras

– Claypans– Fragipans– Plinthite– Caliche and duripans

Any harden layer is called a pan

Claypans occur with extreme illuviation

Fragipans are a hard brittle claypan

Plinthe is a tropical hardpan that can not be soften by wetting

Caliche and duripans, layer of soil cemented by lime cement leaving white hardened layer

PORI TANAH - POROSITAS

• If you compact or till a soil,

the pore space decreases.• Large pores are filled with air• Small pores are filled with water• Clay soils have greater total pore space

than sandy soils

% PS = 100 * (1-[Db/Dp])

Porositas tanah erat hubungannya dengan bulk density serta permeabilitas.

Apabila total ruang pori tinggi maka memiliki tekstur tanah yang halus yang dapat menyimpan air dan

udara dalam tanah sehingga menyebabkan kerapatan massa (bulk density) yang rendah.

% Pore Space = 100 * (1-[Db/Dp])

PORI TANAH - POROSITASPermeabilitas merupakan kemampuan tanah untuk

meneruskan air atau udara. Permeabilitas umumnya diukur sehubungan laju aliran air melalui tanah dalam

suatu massa waktu dan dinyatakan sebagai cm per jam. Hal ini mengakibatkan pergerakan udara yang

berhubungan dengan volume tanah yang kosong, bukan ukuran pori dan kesinambungan ruang pori.

40

45

50

55

60

65

1 1.1 1.2 1.3 1.4 1.5 1.6

Bulk density (Mg/m3)

Pore

spac

e (%

)

h Clay content

A pattern to note: As clay content increases, pore volume increases and bulk density decreases

PORI TANAH - POROSITAS

PORI MAKRO - MIKRO

Macropores are usually air-filled,

whereas micropores are typically water-

filled

The size of pores rather than their combined

volume is the important factor in determining soil drainage, aeration, and

other processes

HUBUNGAN TEKSTUR DENGAN PORI (data for 10 cm depth)

Texture O.M. (%)

Total pore space (%)

Micropores (%)

Macropores (%)

Sandy loam

2 42

Silt loam• good structure

• poor structure

5

5

50

50

17 25

27 23

40 10

• Color as a guide to soil use– Dark brown to black– White to light gray– Light brown, yellow to red– Bluish-gray– Mottled colors

• Describing soil color

WARNA TANAH

http://www.egyptastic.co.uk/_25.html …. Diunduh 15/2/2012

• Hue (e.g., 5R) tells you general shade; DOES NOT tell you how dark the soil is

• Value (e.g., 5R 5/ ) tells you how dark the soil is: (0 darkest) may indicate current moisture status (dark = wet) and/or amount of organic matter

• Chroma (e.g., 5R 5/8) tells you color intensity (0 = gray). Indicator of hydrologic regime (well drained = O2 = high chroma)

“quantified” using the Munsell system

WARNA TANAH

Hue, Value & Chroma

WARNA TANAH

WARNA TANAH

Tanah-tanah coklat tua hingga hitam

• O.M. can reach high level in waterlogged soil• Usually smells sour, oily• O.M. can also reach high level in aerated soil. It smells

earthy• Dark parent materials can affect color of soil..smells

chalky

Soil color Soil attributes Environmental

conditions

Brown to black (surface horizon)

accumulation of organic matter (OM), humus

low temperature, high annual precipitation

amounts, soils high in soil moisture, and/or litter from coniferous trees favor an

accumulation of OM

Tanah-tanah Putih hingga Kelabu Muda

Light color may indicate the presence of chemicals such as gypsum or other salts

Munsell soil color chart. http://www.soils.wisc.edu/courses/SS325/morphology.htm#color

diunduh 15/2/2012

Tanah-tanah Coklat muda, Kuning, Merah

• Indicate iron oxides, indicates good drainage• Blue-gray soils indicate a lack of oxygen in the

soil• Mottled wetland soils indicate waterlogged soil

for at least part of the year

Bright-light Eluvial horizon

(E horizon)

In environments where precipitation >

evapotranspiration there is leaching of sequioxides, carbonates, and silicate

clays. The eluviated horizon consists mainly of silica

Yellow to reddish

Fe3+ (oxidized iron)

Well-aerated soils

Soil color Soil attributes Environmental conditions

Deskripsi Warna Tanah• The Munsell system is a widely used color I.D. system

• Hue is the color such as red or yellow

• Value is the lightness or darkness of hue noted by numbers zero to ten

• Chroma is the purity of the dominate color denoted by a number

http://vro.dpi.vic.gov.au/dpi/vro/vrosite.nsf/pages/soilhealth_prac_soil_colour

diunduh 15/2/2012

SISTEM MUNSELL• A 10YR3/6 soil has:• The hue 10YR, a yellow red• The value of 3 (dark)• Chroma of 6• This is described as a dark yellow brown soil• This would be recognized internationally

WARNA TANAH - DRAINAGE

http://www.hindawi.com/journals/aess/2012/430347/fig2/ ….. Diunduh 15/2/2012

DRAINAGE INTERNAL TANAH.

http://sis.agr.gc.ca/cansis/nsdb/detailed/name/drainage.html … Diunduh 15/2/2012

Important for proper plant growth

Permeability can be determined by the color of the subsoil.

Grey with some red or yellow streaks - poorly drained soils

Yellowish-brown or reddish brown with some grey mottling - as internal drainage improves

Uniform bright color with few or no grey streaks or mottling – good internal drainage and aeration

Poorly drained

Water is removed so slowly in relation to supply that the soil remains wet for a comparatively large part of the time the soil

is not frozen. Excess water is evident in the soil for a large part of the time.

Subsurface flow or groundwater flow, or both, in addition to precipitation are the main water sources; there may also be a

perched water table, with precipitation exceeding evapotranspiration.

Soils have a wide range in available water storage capacity, texture, and depth, and are gleyed subgroups, Gleysols, and

Organic soils.