dasar ilmu tanah

POKOK BAHASAN DASAR-DASAR ILMU TANAH
I. PENDAHULUAN:
Pengertian tanah,
Konsep tanah, dan
Linkup Kajian tanah
II. KOMPONEN TANAH
Bahan Anorganik
Bahan Organik Tanah
Udara tanah
Air Tanah
III. PEMBENTUKAN TANAH
Faktor Pembentuk Tanah (Iklim, Batuan, Organisme, Relief, Waktu),
Pelapukan
Profil Tanah
IV. SIFAT FISIKA TANAH
Warna Tanah
Tekstur Tanah
Struktur Tanah
Konsistensi tanah
Bji, BJp. Porositas Tanah
UJIAN TENGAH SEMESTER
II. KOMPONEN TANAH
Soil is dynamic resouce (sumber daya) that support plant life.
Tanah adalah sistem dispersi. It is made up of different sized mineral
particles (sand, silt, and clay) organic matter, and numerous species
of living organism.
Bahan utama penyusun tanah:
1.
Bahan mineral (anorganik) (45-50 %)
2.
Bahan organik ( 0 - 5 %)
3.
Air (20 – 30 %)
4.
Udara (20 – 30 %)
Komposisi ini berbeda untuk tiap jenis tanah ataupun tiap lapisan tanah
Soil = is a complex mixture of
weathered rock fragments, minerals, water
and the remains of dead
plants and animals air
 Rock and mineral
fragments produced by
weathering (regolith) that
supports the growth of
plants
 Humus (decayed animal and
plant remains) is a small,
but essential, component
Kering
Kapasitas lapangan
Bhn. Mineral
Bhn. Mineral
Udara tanah
50 %
Titik layu tetap
A. Anorganik
• Bahan mineral berasal dari pelapukan batuan
• Apa itu batu (rock) atau batuan (sione)?
• Batuan dikelompokkan:
1. batuan beku (ignius, batu api)
2. batuan sedimen (endapan, mendapan)
3. batuan metamorfik (alihan, malihan)
Aliran lava
Figure 4.7 A
Granite
Rhyolite
Diorite
Andesite
Gabbro
Figure 4.7 C
Basalt
Clastic Sedimentary Rocks
Breccia - fragmental
A BRECCIA is made of varying
sizes of angular fragments
cemented together. The
name is from the Italian word
for “broken stones” or
“rubble”.
Many form as the result of fault
movement; others form as the
result of rapid and short
transportation, such as
landslides.
Clastic Sedimentary Rocks
Conglomerate - fragmental
CONGLOMERATES are very
similar to breccias, but the
fragments are rounded.
The name is from the Latin
conglomeratus for “heaped,
rolled or pressed together”.
These rocks form in alluvial
fans, stream beds and
pebble beaches.
Clastic Sedimentary Rocks
Sandstone - fragmental
SANDSTONE is made up of
fine-grained particles (1/16
–2 mm). The sand grains
(often quartz) are
commonly cemented by
silica, carbonates, clay or
iron oxides. Sandstone is
identified by its sandy
texture – which often
translates into a gritty feel.
Environments in which
sandstones form include
beaches, sand bars, deltas
and dunes.
Coconino Sandstone, the
result of a Permian age
coastal dune field
Clastic Sedimentary Rocks
Shale - fragmental
SHALE is a very common
rock made of silt and clay
sized particles. It is
generally very thin-bedded
and splits along the bedding
planes. In fact, the name is
probably from the Old
English scealu, “shell or
husk”. Normally gray to
black, shale may be brown
to dark red, depending on
the amount of included iron
oxide.
Shales form in quiet environments, such as lakes,
swamps, deltas and offshore
marine.
Black shale, deposited in a offshore basin in
a Middle Cambrian sea. Wheeler Shale
with trilobite fossil (Elrathia kingii)
Fish scales
Utah
2. Biochemical Sedimentary Rocks
COAL - Biochemical
COAL is considered a rock,
although it is not composed
of minerals, but rather the
decomposed remains of
large volumes of vegetation
that accumulated in a wet,
low oxygen environment,
such as a swamp or marsh.
Peat, Lignite and SubBituminous & Bituminous
are sedimentary varieties of
coal and are used as fuels.
Biochemical Sedimentary Rocks
DIATOMITE - Biochemical
DIATOMITE, also
known as diatomaceous
earth, is composed of the
siliceous shells of
microscopic alga called
diatoms. It is light weight
and is generally white.
San Manuel, AZ
Diatomite is used as an
abrasive, insecticide,
filtering medium, and
paint “flattener”.
3. Chemical Sedimentary Rocks
Limestone -
chemical
Uses:
LIMESTONE is composed
 Manufacture of lime and Portland
primarily of calcite. Generally
cement & to neutralize smokestack
it is dense, fine-grained, and
gases.
usually white to dark gray. Its
 Finely ground, used as a functional
most distinguishing feature is
filler in products such as paint,
countertops & plastics.
its solubility in weak
 The dust on chewing gum is
hydrochloric or acetic acid
ground limestone.
accompanied by brisk
 Mild abrasive additive to
effervescence.
toothpaste.
 Soil conditioner
The environment of deposition if
 Flux in processing iron and copper
generally warm, shallow seas.
ores.
Therefore, marine invertebrate
 Building and ornamental stone.
fossils are common.
Chemical Sedimentary Rocks
Limestone - chemical
Coquina
Crystalline
Pleistocene, Rocky Point,
Mexico
Redwall Limestone
Travertine
Mayer, AZ
Fossiliferous
Chemical Sedimentary Rocks
CHERT - chemical
CHERT is crypto-crystalline
quartz. It is often the result
of the dissolution of
volcanic ash and is
sometimes found in
extensive beds, such as the
novaculite of Arkansas.
It has waxy luster, is
translucent and fractures
conchoidally. Chert can be
any color, but extensive
beds are generally white to
gray.
Chemical Sedimentary Rocks
GYPSUM - chemical
Satin Spar
Alabaster
Selenite
Gypsum & Anhydrite (water-less
calcium sulfate), Carlsbad, NM
GYPSUM (calcium sulfate) is
found in geographically widespread deposits resulting
from the evaporation of a
body of water, such as ocean
basin or playa lake.
It is soft (H=2) & usually white
to gray. Three varieties are:
Alabaster, Satin Spar and
Selenite.
Gypsum is mined for use in
wallboard and plasters, as an
agricultural amendment and
to control the set/cure time of
Portland cement.
Chemical Sedimentary Rocks
ROCK SALT - chemical
ROCK SALT (halite –
sodium chloride) is also a
deposit resulting from
evaporation of a marine
basin or playa lake.
It has cubic cleavage and
tastes salty.
Rock salt is used as a source
of chlorine and sodium, as
a food supplement, in
water softeners and as a
road de-icer.
Halite Trona, CA
SLATE - foliated
SLATE is derived from shale.
It is a dense,
microcrystalline rock, but
one in which parallel planes
are very evident in its slaty
foliation – a feature
resulting from the alignment
of clay and mica
minerals,which allows it to
split readily into sheets. It
may be gray, black, green or
red.
Uses include roofing,
flagstone, pool table tops
and “blackboards”.
Note the relatively dull luster of slate.
PHYLLITE - foliated
PHYLLITE is
somewhat more
metamorphosed than
slate. The platy
crystals of mica have
grown and the rock
displays a subtle, satiny
shine referred to as
“phyllitic sheen”. The
name comes from its
leaf-like (many fine
layers) appearance.
Note the phyllitic sheen.
SCHIST - foliated
SCHIST is medium to coarsegrained, crystalline, with
prominent parallel mineral
orientation. Typically, it is
predominately muscovite mica,
which lends a silvery white to
gray sparkly appearance. It is
not unusual for accessory
minerals (such as garnets,
staurolite, tourmaline) to grow
in the rock.
Schist is added to clay mixtures
as a strengthening material in
vitreous pipe (red sewer) and
clay roof tiles.
Crumpling of schist due to
pressure and collapse of
mica crystals
tourmaline
porphyroblast –
note alignment
garnet
porphyroblast
GNEISS - foliated
GNEISS formed under
conditions of high
temperatures and pressures
at great depth during regional
metamorphism. It is
characterized by foliation
expressed as black and white
banding. Because the rock
becomes plastic, the banding
is often contorted (squiggly).
Gneissic granite –
separation of dark
& light minerals is
just beginning
Well banded gneiss
Augen = quartz
pebble resistant to
compression
Augen Gneiss
kink in gneiss
metamorphism of shale
SHALE is the most common sedimentary rock.
Through the agents of metamorphism it changes to rocks that are stable at
higher temperatures and pressures.
These changes take place in the solid state.
GRANITE
MELTING Produces
GRANITE
Slate
Shale
Increasing Temperature and Pressure
Schist
Phyllite Gneiss
MARBLE – non-foliated
Hewitt Canyon, AZ
MARBLE is metamorphosed
limestone or dolomite. The
colors can vary from pure
white to gray, green, yellow,
brown, black, red or any
combination thereof,
depending on the
‘impurities’ in the parent
limestone. Bands or streaks
result from plastic flow
during extreme deformation,
due to high pressure and
temperature.
It is calcite or dolomite and
will fizz in weak acids.
Marble is used for building
facades, floors, countertops,
statuary, landscaping,
paving/roofing, poultry grit,
and as filler/extender for
paint, plastics, paper and
adhesives.
QUARTZITE – non-foliated
QUARTZITE is metamor-phosed quartz sand-stone. It is a very
dense,durable, massive, microcrystalline rock (but still may retain a slightly
sandy look). It can be any color, but tends to be white, tan or pink.
SERPENTINITE – non-foliated
Chrysotile
asbestos
Salt River Canyon, AZ
SERPENTINITE is
composed of one or
more minerals in the
serpentine family. It is
common where wet
basalts or mantle rocks
are metamorphosed,
such as at convergent
boundaries.
Its green colors, waxy
luster, often associated
asbestos and common
slickensided surfaces
are clues to its identity.
METACONGLOMERATE – non-foliated
Conglomerate
METACONGLOMERATE is
metamorphosed
conglomerate. It retains its
pebbly appearance, but while
a sedimentary conglomerate
will break around the pebbles,
a metaconglomerate will
break through the pebbles.
If temperatures are high enough
in the presence of pressure,
the pebbles may become
squished or flattened and will
be elongated parallel to each
other (becomes foliated).
The other rock
Primitive Rocks
“primitive rocks” formed
directly from the protosolar
nebula.
Examples of primitive rocks
include chondritic meteoritic
material. Elemental ratios are
in the same ratio as those in
the Sun. We will talk more
about these when we survey
asteroids.
Iklim,
B. Beku
relief
B. Endapan
organisme
B. Malihan
waktu
TANAH
PADATAN TANAH
…
• Terdapat dalam berbagai ukuran:
50 µm – 2.000 µm  pasir
2 – 50 µm  debu (lanau)
<2µ
 klei (liat = lempung)
Bahan mineral > 2 mm terdiri atas kerikil,
kerakal, dan bongkah
Padatan tanah
Ukuran dan Susunan
Ukuran diameter
> 2,0 mm  batu/batuan
2,0-20 mm kerikil
< 2,0 mm  bahan tanah halus (fine earth)
Bahan tanah halus
-pasir 2,00-0,02 mm
pasir kasar 2,0-0,2 mm
pasir halus 0,2-0,02 mm
Sistem International
- lanau 0,02-0,002 mm
- klei < 0,002 mm (lempung UGM+ITB, liat IPB):
Bahan tanah halus
Pasir : 0,05 – 2,00 mm
Pasir sangat kasar
Pasir kasar
Pasir sedang
Pasir halus
Pasir sangat halus
2,00 – 1,00 mm
1,00- 0,50 mm
0,50 – 0,25 mm
0,25 - 1,00 mm
0,10 - 0,05 mm
Lanau 0,05 -0,002 mm
lanau kasar 0,05 – 0,02 mm
lanau sedang 0,02-0,005 mm
lanau halus 0,005-0,002 mm
Klei < 0,002 mm
Klei kasar 0,002-0,0002 mm
Klei sedang 0,0002-0,00008 mm
Klei halus < 0,0008 mm
USDA system
Klei dapat berarti
= ukuran < 0,002 mm (org./anorg.)
= mineral (anorganik)
= tekstur
Bentuk padatan
batang
lempeng
gumpal menyudut/membulat
tidak teratur
bola
A. MINERAL PRIMER & SEKUNDER
Mineral primer: mineral yang berasal langsung dari
pembekuan magma (terdapat pada fraksi pasir dan
debu)
Mineral sekunder: mineral hasil bentukan pelapukan
dan pembentukan tanah (terdapat pada fraksi klei)
Mineral Primer dalam tanah
mineral
Formula
Keterangan
Kuarsa
SiO2
Tektosislikat
Muskovit
KAl2(AlSi3O10)(OH)2
Filosilikat
Biotit
K(Al,Fe)(AlSi3O10)(OH)2
Filosilikat
Felspar
ortoklas
mikrolin
Albit
Amfibol
(Termolin)
Filosilikat
K[AlSi3O8 ]
K[AlSi3O8]
Na[AlSi3O8]
Ca2Mg5Si8O22(OH)2
Inosilkat ganda
Piroksen
enstatit
diopsit
rhodonit
Inosilkat tunggal
MgSiO3
Ca,Mg (Si2O6)
MnSiO3
olivin
(Mg, Fe)SiO4
Nesosilkat / Sorosilikat
Epidot
Ca2(Al, Fe)3Si3O12 (OH)
Inosilikat tunggal
MINERAL PRIMER TANAH DAN UNSUR HARA
------------------------------------------------------------------------Mineral
Unsur hara
------------------------------------------------------------------------Kuarsa (SiO2)
-Kalsit
Ca
Dolomit
Ca, Mg
Feldspar: - Ortoklas
K
- Plagioklas
Na, Ca
Mika:
- Muskovit
K
- Biotit
K, Fe
Amfibol (hornblende)
Ca, Mg, Fe, Na
---------------------------------------------------------------------------
MINERAL PRIMER TANAH DAN UNSUR HARA
-------------------------------------------------------Mineral
Unsur hara
-------------------------------------------------------Piroksin
Ca, Mg, Fe
Olivin
Mg, Fe
Leusit
K
Apatit
P
--------------------------------------------------------
MINERAL SEKUNDER
Beberapa jenis mineral sekunder (mineral liat)
yang sering ditemukan di dalam tanah:
1. Kaolinit
2. Haloisit
3. Montmorilonit
4. Gibsit
5. Al-Fe oksida
Mineral Primer dan sekunder dalam tanah
Nama mineral
Formula
Mineral klei
Kaolinit
Si4Al4O10(OH)8
Monmorillonit
Mx (Al, Fe, Mg) Si8O20(OH)4
Vermikulit
Chlorit
(Al,Mg,Fe)(Si,Al)8O20(OH)4
[M,Al,(OH)6](Al, Mg)4(Si,Al)8O20(OH)4
Alofan
Si3Al4O12. nH2O
Imogolit
Si2Al4O10.5H2O
Hematit
α-Fe2O3
Maghemit
γ-Fe2O3
Goetit
FeOOH
Ferihidrit
Fe10O15.9H2O
Boehmit
γ-AlOOH
B. BAHAN ORGANIK
• Bahan organik kasar (particulate)
• Bahan organik halus (humus)
• Humus terdiri dari bahan organik halus, berasal
dari hancuran bahan organik kasar, serta
senyawa baru yang dibentuk dari hancuran
bahan organik tersebut melalui kegiatan
mikroba dalam tanah
Komponen organik
Sisa (residu) organik dan rombakan jaringan jasad
Biomasa tanah (flora dan fauna tanah)
Humus = bahan organik tanah
Akar tumbuh an hidup
10 % b kering
Humus
85 % berat
kering
Flora dan fauna tanah (edafon)
5 % berat kering, terdiri atas fungi, algae,
bakteri, aktinomicetes, cacingtanah,
makrofauna,
Manfaat Bahan Organik
Pengaruh bahan organik terhadap sifat tanah dan
pertumbuhan tanaman:
-
memperbaiki struktur tanah
sumber hara N, P, S dan unsur mikro
Menambah kemampuan tanah menahan air
Menambah kemampuan tanah untuk menahan
unsur hara
- Sumber energi bagi mikroba
Humus = BOT
Merupakan senyawa yang resisten (tidak mudah
hancur), berwarna hitam atau coklat,
mempunyai daya menahan air dan unsur hara
yang tinggi
Humus mempunyai kapasitas tukar kation yang
tinggi yang disebabkan oleh gugus funsional
(karboksil, karbonil, alkohol, dll.)
Struktur asam humat
Ukuran koloid (1 nm-10um)
Taklarut air
Tanah Organik (Gambut)
Dijumpai di daerah rawa-rawa
Bila kandungan BO > 20 % (untuk tanah pasir)
atau > 30 % (untuk tanah liat) dengan ketebalan
> 40 cm  disebut tanah organik (tanah
gambut)
Top Soil
Tanah yang banyak mengandung humus atau
bahan organik adalah tanah lapisan atas atau
top soil.
Makin ke bawah, kandungan bahan organik
makin berkurang, sehingga tanah makin kurus
(tidak subur)
I. UDARA TANAH
Susunan udara tanah berbeda dengan udara di atmosfir;
1.
2.
3.
Kandungan uap air > tinggi
Kandungan CO2 lebih besar
Kandungan O2 lebih kecil
Udara dan air mengisi pori-pori tanah. Air mengisi pori-pori
mikro, sedangkan udara mengisi pori-pori makro
Udara Tanah dan Atmosfer
Komposisi
Udara tanah
(%)
Udara atmosfer
(%)
N2
O2
CO2
<78
20,6
>0,2
78
21
0,3
Ar
He
CH4
NO2
Sisa
Sisa
Sisa
sisa
Sisa
Sisa
Sisa
sisa
II. AIR TANAH
Air terdapat dalam tanah karena:
(1) Diserap (ditahan) oleh masa tanah
(2) Tertahan oleh lap. kedap air
(3) Keadaan drainase kurang baik.
Fungsi air bagi tanaman:
(1) Sebagai unsur hara  H H O
(2) Sebagai pelarut unsur hara
(3) Sebagai bagian dari sel-sel tanaman
(protoplasma)
Macam-macam Air Tanah
1.
Air tanah (H2O)
a) Air bebas = air gravitasi
b) Air Kapiler = dipegang oleh pori/kapilar tanah
c) Air higroskopis (air yang menyelimuti partikel tanah)
2.
3.
4.
Air tersediakan (KL-TLT)
Air tak tersediakan (<TLT)
Air tak berguna (air bebas)
5.
6.
7.
8.
9.
10.
11.
Kapasitas maksimum (keadaan jenuh)
Kapasitas lapangan (jumlah airtanah setelah air gravitasi
tersingkirkan)
Tara lengas (kadar air disentrifusikan 1000 g, 40 menit)
Titik layu tetap
Kering angin (kadar air setimbang dengan kadar air udara)
Kering oven
2. Larutan Tanah (H2O + solute (linarut)
Kation = Na+, K+, Ca+2, Mg+2, Fe+2, NH4+ H+, Al+3
Anion = SiO4-4, H2PO4-, HPO4-2,SO4-2, NO3-1, BO3-3
MACAM AIR TANAH …
1.
Air higroskopik
Air yang diserap tanah sangat kuat sehingga tidak dapat
digunakan tanaman
2.
Air kapiler
Air yang dapat bergerak ke samping atau ke atas karena
gaya kapiler. Sebagian besar air kapiler merupakan air
yang tersedia bagi tanaman
3.
Air gravitasi
Air yang tidak dapat diserap tanah karena adanya
pengaruh gaya gravitasi
Air kapiler (tersedia bagi tanaman)
(1) Kapasitas lapangan
Menunjukkan jumlah air terbanyak yang dapat
ditahan oleh tanah
(2) Titik layu permanen
Pada kondisi ini, akar tanaman mulai tidak mampu
lagi menyerap air dari tanah, sehingga tanaman
menjadi layu
(3) Air tersedia
Merupakan selisih antara kadar air pada kapasitas
lapang dan kadar air pada titik layu permanen
TEGANGAN AIR TANAH
Kandungan air pada kapasitas lapangan ditunjukkan
oleh kandungan air pada tegangan 1/3 bar, sedangkan
kandungan air pada titik layu permanen adalah pada
tegangan 15 bar.
Air yang tersedia bagi tanaman terletak pada tegangan
1/3 – 15 bar
Tegangan air
------------------------------------------------------------------------Kelembaban tanah
Tegangan air
Bar (atm)
pF
------------------------------------------------------------------------Jenuh air
0
0
Kapasitas lapang
1/3
2,53
Titik layu permanen
15
4,18
Koefisien higroskopik 31
4,50
Kering oven
10.000
7,0
------------------------------------------------------------------------
Soil profiles
A
AO
E
B
C
O
E
Bt
R
TUGAS
1.
Jelaskan pengertian tanah ditinjau dari segi
pertanian
2. Jelaskan perbedaan antara pedologi dan
edafologi
3. Sebutkan ilmu-ilmu yang berhubungan dengan
ilmu tanah
4. Sebutkan komponen utama tanah