Transcript SIFAT FISIKA TANAH BAHAN KAJIAN MK. DASAR ILMU TANAH

BAHAN KAJIAN
MK. DASAR ILMU TANAH
SIFAT
FISIKA TANAH
Dihimpun oleh
Soemarno
Jurusan Tanah FP UB Februari 2012
TEKSTUR TANAH
Efek Ukuran partikel tanah
Tipe-Tipe Struktur Tanah
Plow layer
Granular
Platy
Prismatic
Columnar
Blocky
Common to Ohio
soils just below Ap
(> 8”)
Single Grain
Sand
Massive
Deeper in profile
(>3-4’)
… Diunduh 15/2/2012
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.
TEKSTUR TANAH
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
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 diameter
Silt - 0.002 mm to 0.05 mm in diameter
Clay - <0.002 mm
Gravel - 2 mm to 2 cm
Stones - >2 cm
Particles of <0.001 mm are designated as colloids - clay, a
colloid is unique because of its large surface area.
TEKSTUR TANAH
• Klasifikasi tekstur tanah
• Penentuan tekstur tanah
TEKSTUR TANAH
• Karakteristik kelas tekstur
• Modifiksi tekstur tanah
Perbandingan ukuran partikel tanah
“Big”  smaller 
really small
Sand  silt 
clay
TEKSTUR TANAH
• Surface area per unit volume
– 1 g sand ~ 0.1 m2
– 1 g silt ~ 1 m2
lowest
– 1 g clay ~ 10-1000 m2
•
•
highest
Gee whiz
fact:
Fine clay has
~10,000
times as
much
surface area
as the same
wt. med.
grain sand
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
h Surface area h weathering
Surface area, pore volume, nutrient
supply capacity, plasticity and cohesion,
swelling
Clay
Silt
Particle Size
Sand
Clay
Silt
Sand
Particle Size
Pore size, infiltration rate, drainage rate, aeration
Siklus Hidrologi dan Tanah
Sifat tanah yang menjadi bagian dari siklus hidrologi.
Moisture
Color
Temperature
Structure
pH
Texture
Horizon
Depths
Bulk
Density
PENGARUH TEKSTUR
Pasir
Water-holding
capacity
Debu
Liat
Low
Medium
High
Aeration
Good
Medium
Poor
Drainage
Fast
Slow
Very slow
Nutrient
retention
Low
Medium
High
DENSITAS DAN
PERMEABILITAS TANAH
• Kerapatan partikel = Particle density
DENSITAS DAN
PERMEABILITAS TANAH
• Bobot Isi Tanah
• Porositas 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 )
DENSITAS DAN
PERMEABILITAS TANAH
Permeability
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 dikeringovenkan per satuan volume.
http://dasar2ilmutanah.blogspot.com/2009/04/sifat-fisika-tanah-bagian-3bobot-isi.html ..... Diunduh 16/2/2012
BOBOT ISI – BULK DENSITY
• Density
particle density: mass per unit volume (not pore
space)
• Porosity
~ 2.65
– Mg/m3 (Dp of quartz mineral, dominant mineral in most soils)
bulk density: mass per unit volume (including pore
space)
ranges 0.1 – 2.65 Mg/m3
the volume
percentage (%)
of the total bulk
soil NOT
occupied by
solids
BOBOT ISI – BULK DENSITY
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
Pore volume
• O.M. decreases bulk density
• Compaction increases bulk
density
• Increased bulk density
lowers water infiltration and
restricts root growth
Clay
Silt
Sand
Particle Size
BOBOT ISI – BULK DENSITY
• Histosols (0.1-0.7 Mg/m3)
LOW
• 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)
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
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
BOBOT ISI – BULK DENSITY
????
Clear
cut
Depth
Forest
Bulk density
Effect varies with soil texture!
Soil bulk density on skid trails: does
tillage help??
Bulk density (g/cm^3)
1.15
1.1
1.05
1
0.95
0.9
0.85
0.8
control
untilled
tilled
BOBOT ISI – BULK DENSITY
Texture
Coarse
Yrs
Increase in Db due
cropped
to texture and
cultivation
Loam
58
0.18
Silt loam
40
0.26
Clay
70
0.30
Fine
In general, the finer the texture, the more
it compacts if aggregates are destroyed
BOBOT ISI – BULK DENSITY
STRUKTUR TANAH
Tanah tidak berstruktur
STRUKTUR TANAH
• Tipe-tipe struktur tanah
• Pembentuka 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.
STRUKTUR TANAH
• Structure
–
spatial arrangement of primary
soil particles
• Aggregate stability
–
how easily or not do the
peds fall apart?
Goal of
good
soil
mgmt.
Low bulk density
Lots of macropores
Stable aggregates
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
Particles bind because organic compounds and some minerals
are “sticky”
– Biological sources: polysaccharides, proteins,
bacterial “glues”
– Mineralogical sources : oxides, carbonates, silicates
(clay particles)
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
KARAKTERISASI STRUKTUR
• Type: Shape of the aggregates
– Four (4) principal shapes
• Granular (A), platy (E), blocky (B),
prismatic (B)
• Size
– fine, medium, coarse
• Grade: distinctness (how obvious)
– Strong, moderate, or weak
• In general,
– if lots of clay STRONG structure,
bigger blocks
– If lots of OM granular structure
TIPE STRUKTUR: Spheroidal
Structure type: Platey
Structure type: Blocky
Structure type: Prism-like
Sodium induced –
disperses clays
A
Granular
E
Platy
B
Blocky
C
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
The same things that lead to
strong structure make stable
aggregates!
• Amount of OM
• Type and amount of clay
• Amount of stabilizing/flocculating
minerals (calcium carbonate,
gypsum, etc.)
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.
2.
3.
4.
5.
Low disturbance
High root abundance
High fungal biomass
High OM
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-PMO), yang saling berikatan dengan partikel (L-PMO) lainnya membentuk makroagregat [(L-PMO)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
KONSISTENSI TANAH
Wet soil
Moist soil
Dry soil
Soil consistency states for a sand and a clay soil (friable soil is best for
tillage).
SIFAT OLAH TANAH
•
•
•
•
•
•
Compaction
Aggregate destruction
Puddling and clods
Surface crusts
Improving tilth
Soil channels
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
year
59% 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
1.32
g
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
% PS = 100 * (1-[Db/Dp])
• 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
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.
PORI TANAH - POROSITAS
Permeabilitas 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.
% Pore Space = 100 * (1-[Db/Dp])
PORI TANAH - POROSITAS
A pattern to note: As clay content increases, pore
volume increases and bulk density decreases
Pore space (%)
65
60
55
50
45
40
1
h Clay content
1.1
1.2
1.3
1.4
Bulk density (Mg/m3)
1.5
1.6
PORI MAKRO - MIKRO
The size of pores rather
than their combined
volume is the important
factor in determining soil
drainage, aeration, and
other processes
Macropores are
usually air-filled,
whereas micropores
are typically waterfilled
HUBUNGAN TEKSTUR DENGAN PORI
(data for 10 cm depth)
Texture
Sandy
loam
O.M. Total pore Micropores Macropores
(%) space (%)
(%)
(%)
2
42
17
25
Silt loam
• good
structure
5
50
27
23
• poor
structure
5
50
40
10
WARNA TANAH
• 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
http://www.egyptastic.co.uk/_25.html …. Diunduh 15/2/2012
WARNA TANAH
“quantified” using the
Munsell system
• 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 = h O2 = high chroma)
WARNA TANAH
Hue,
Value &
Chroma
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
Brown to black
(surface
horizon)
Soil attributes
Environmental
conditions
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
Soil color
Soil attributes
Environmental conditions
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
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_colo
ur 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.
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.
http://sis.agr.gc.ca/cansis/nsdb/detailed/name/drainage.html … Diunduh
15/2/2012