sifat dan ciri fisika tanah
TRANSCRIPT
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.