Download - kompendium air – lengas tanah
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Bahan kajian pada MK DASAR ILMU TANAH
AIR – LENGAS TANAH
Disarikan oleh: SMNO.jursntnhfpub.Sept2012
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CIRI-CIRI TANAH• Tekstur Tanah
– Definition: relative proportions of various sizes of individual soil particles
– USDA classifications• Sand: 0.05 – 2.0 mm• Silt: 0.002 - 0.05 mm• Clay: <0.002 mm
– Textural triangle: USDA Textural Classes– Coarse vs. Fine, Light vs. Heavy– Affects water movement and storage
• Struktur Tanah– Definition: how soil particles are grouped or
arranged– Affects root penetration and water intake and
movement
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USDA Textural TriangleSEGITIGA TEKSTUR
TANAH
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• Bulk Density (b)
– b = soil bulk density, g/cm3
– Ms = mass of dry soil, g– Vb = volume of soil sample, cm3
• Typical values: 1.1 - 1.6 g/cm3
• Particle Density (p)
– P = soil particle density, g/cm3
– Ms = mass of dry soil, g– Vs = volume of solids, cm3
• Typical values: 2.6 - 2.7 g/cm3
b
sbVM
ps
s
MV
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• Porositas tanah ()
• Nilai-nilai yang khas: 30 - 60%
volume of poresvolume of soil
1 100%b
p
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AIR DALAM TANAH
• Kadar Air (Lengas) Tanah
– Mass water content (m)– m = mass water content (fraction)– Mw = mass of water evaporated, g
(24 hours @ 105oC)– Ms = mass of dry soil, g
s
wm
MM
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• Kadar air volumetrik (v)
– V = volumetric water content (fraction)– Vw = volume of water– Vb = volume of soil sample– At saturation, V = – V = As m
– As = apparent soil specific gravity = b/w (w = density of water = 1 g/cm3)
– As = b numerically when units of g/cm3 are used• Ekuivalen kedalaman air (d)
– d = volume of water per unit land area = (v A L) / A = v L– d = equivalent depth of water in a soil layer– L = depth (thickness) of the soil layer
vw
b
VV
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Kadar air volumetrik & Kedalaman ekuivalen
(g) (g)
(cm3)
(cm3)
Equivalent Depth
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1 in.
0.50 in.
0.15 in.
0.20 in.
0.15 in.
Soil Solids (Particles): 50%
Total Pore Space: 50%
Very Large Pores: 15% (Gravitational Water)
Medium-sized Pores: 20% (Plant Available Water)
Very Small Pores: 15% (Unavailable Water)
Kadar air volumetrik & Kedalaman ekuivalen
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Daya Simpan Air = Water-Holding Capacity of Soil
Effect of Soil Texture
Coarse Sand Silty Clay Loam
Gravitational WaterWater Holding CapacityAvailable WaterUnavailable Water
Dry Soil
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POTENSIAL AIR TANAH
• DESKRIPSI– Ukuran dari status energi air tanah– Important because it reflects how hard plants must
work to extract water– Units of measure are normally bars or
atmospheres– Soil water potentials are negative pressures
(tension or suction)
– Water flows from a higher (less negative) potential to a lower (more negative) potential
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Komponen
– t = total potensial air tanah– g = gravitational potential (force of gravity pulling on the
water)– m = matric potential (force placed on the water by the
soil matrix – soil water “tension”)– o = osmotic potential (due to the difference in salt
concentration across a semi-permeable membrane, such as a plant root)
– Matric potential, m, normally has the greatest effect on release of water from soil to plants
t g m o
POTENSIAL AIR TANAH
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Kurva pelepasan air tanah :– Curve of matric potential (tension) vs. water content– Less water more tension– At a given tension, finer-textured soils retain more
water (larger number of small pores)
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Height of capillary rise inversely related to tube diameter
Potential Matriks dan Tekstur TanahThe tension or suction created by small capillary tubes (small soil pores) is
greater that that created by large tubes (large soil pores). At any given matric potential coarse soils hold less water than fine-textured soils.
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Kapasitas Lapang= Field Capacity (FC or fc)1. Soil water content where gravity drainage becomes negligible2. Soil is not saturated but still a very wet condition3. Traditionally defined as the water content corresponding to a
soil water potential of -1/10 to -1/3 bar
Titik Layu Permanen: Permanent Wilting Point (WP or wp)4. Soil water content beyond which plants cannot recover from
water stress (dead)5. Still some water in the soil but not enough to be of use to
plants6. Traditionally defined as the water content corresponding to -
15 bars of SWP
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Relasi-relasi Lengas Tanah
Diunduh dari: Soil Water Phases - N. Sivakugan
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Menghitung masa (atau bobot) dan volume dari tiga fase yang berbeda
soil
air
water
Vs
Va Ma=0
Ms
MwMt
Vw
Vv
Vt
Diagram Fase
NotationM = mass or weightV = volumes = soil grainsw = watera = airv = voidst = total
• Diunduh dari: Soil Water Phases - N. Sivakugan
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DefinisiKadar air (w) merupakan ukuran air yang
ada dalam tanah.
soil
air
water
Vs
Va Ma=0
Ms
MwMt
Vw
Vv
Vt
Phase Diagram
S
W
MMw
Expressed as percentage.
Range = 0 – 100+%.
X 100%
• Diunduh dari: Soil Water Phases - N. Sivakugan
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Definisi:Void ratio (e) is a measure of the void volume.
soil
air
water
Vs
Va Ma=0
Ms
MwMt
Vw
Vv
Vt
Phase Diagram
S
V
VVe
• Diunduh dari: Soil Water Phases - N. Sivakugan
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Definisi:Porosity (n) is also a measure of the void volume, expressed as
a percentage.
soil
air
water
Vs
Va Ma=0
Ms
MwMt
Vw
Vv
Vt
Phase Diagram
T
V
VVn X 100%
Theoretical range: 0 – 100%
Diunduh dari: Soil Water Phases - N. Sivakugan
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DefinisiDerajat kejenuhan (S): persentase pori yang terisi air .
soil
air
water
Vs
Va Ma=0
Ms
MwMt
Vw
Vv
Vt
Phase Diagram
V
W
VVS
Range: 0 – 100%
X 100%
DrySaturated
• Diunduh dari: Soil Water Phases - N. Sivakugan
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Contoh sederhana:
water
air
soil
Dalam ilustrasi ini:
e = 1
n = 50%
S = 50%
• Diunduh dari: Soil Water Phases - N. Sivakugan
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DefinisiBobot Isi (m) adalah kerapatan tanah dalam kondisi apa
adanya.
soil
air
water
Vs
Va Ma=0
Ms
MwMt
Vw
Vv
Vt
Phase Diagram
T
Tm V
M
Units: t/m3, g/ml, kg/m3
• Diunduh dari: Soil Water Phases - N. Sivakugan
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DefinisiSaturated density (sat) is the density of the soil
when the voids are filled with water.
Submerged density (’) is the effective density of the soil when it is submerged.
’ = sat - w
• Diunduh dari: Soil Water Phases - N. Sivakugan
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DefinisiKerapatan kering (d) : kerapatan tanah pada kondisi
kering.
soil
air
water
Vs
Va Ma=0
Ms
MwMt
Vw
Vv
Vt
Diagram Fase
T
Sd V
M
Units: t/m3, g/ml, kg/m3
• Diunduh dari: Soil Water Phases - N. Sivakugan
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DefinisiBulk, saturated, dry and submerged unit weights ()
are defined in a similar manner.
= g
Here, use weight (kN) instead of mass (kg).
Berat jenis (kerapatan jenis) partikel tanah (Gs) biasanya berkisar antara 2.6 dan 2.8.
kg/m3N/m3 m/s2
• Diunduh dari: Soil Water Phases - N. Sivakugan
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Hubungan FasePerhatikan fraksi tanah dimana Vs = 1.
soil
air
water
1 Gsw
SewSe
e
Diagram Fase
The other volumes can be obtained from the previous definitions.
Massa = Kerapatan x Volume
volumes masses
The masses can be obtained from:
• Diunduh dari: Soil Water Phases - N. Sivakugan
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Hubungan FaseDari definisi sebelumnya:
soil
air
water
1 Gsw
SewSe
e
Phase Diagram
SS
W
GSe
MMw
ee
VVnT
V
1
Diunduh dari: Soil Water Phases - N. Sivakugan
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Hubungan Fase
soil
air
water
1 Gsw
SewSe
e
Diagram Fase
WS
T
Tm e
SeGVM
1
WS
T
Tsat e
eGVM
1
WS
T
Sd e
GVM
1
• Diunduh dari: Soil Water Phases - N. Sivakugan
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AIR TANAH TERSEDIA
• Definisi:1. Water held in the soil between field capacity and
permanent wilting point 2. “Tersedia” untuk digunakan oleh tanaman
Kapasitas Air Tersedia: Available Water Capacity (AWC)3. AWC = fc - wp
4. Units: depth of available water per unit depth of soil, “unitless” (in/in, or mm/mm)
5. Measured using field or laboratory methods (described in text)
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Sifat Hidraulik Tanah & Tekstur Tanah
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• Fraksi air-tersedia yang hilanbg dari tanah (fd)
– (fc - v) = soil water deficit (SWD)– v = current soil volumetric water content
• Fraksi air-tersedia yang tertinggal (fr)
– (v - wp) = soil water balance (SWB)
wpfc
vfcdf
wpfc
wpvrf
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• Total Air Tersedia: Total Available Water (TAW)
TAW = (AWC) (Rd)1. TAW = total available water capacity within the plant
root zone, (inches)2. AWC = available water capacity of the soil,
(inches of H2O/inch of soil)3. Rd = depth of the plant root zone, (inches)4. If different soil layers have different AWC’s, need to sum up
the layer-by-layer TAW’s
TAW = (AWC1) (L1) + (AWC2) (L2) + . . . (AWCN) (LN) - L = thickness of soil layer, (inches) - 1, 2, N: subscripts represent each successive soil layer
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Horizontal movement due to capillarityVertical movement
due largely to gravity
Gravity vs. Capillarity
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Infiltrasi Air :Masuknya air ke dalam tanah
Faktor-faktor yang mempengaruhi:• Tekstur tanah• Kandungan-awal lengas tanah• Kerak permukaan (structure, etc.)• Soil cracking• Praktek pengolahan tanah• Metode aplikasi air (e.g., Basin vs. Furrow)• Suhu air.
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Infiltrasi Kumulatif vs. Tekstur Tanah
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Laju Infiltrasi vs. WaktuUntuk tekstur tanah yang berbeda
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Laju Infiltrasi dan Tekstur Tanah
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Laju infiltrasi vs. Laju irigasi konstan
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Laju infiltrasi vs. Laju irigasi beragam
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Kedalaman Penetrasi Air
1. Can be viewed as sequentially filling the soil profile in layers
2. Deep percolation: water penetrating deeper than the bottom of the root zone
3. Pencucian : transport of chemicals from the root zone due to deep percolation
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Simpanan lengas (air) dalam profil tanah yang berlapis-lapis
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Kekuatan ikatan antara molekul air dengan partikel tanah dinyatakan dengan TEGANGAN AIR TANAH. Ini merupakan
fungsi dari gaya-gaya adesi dan kohesi di antara molekul - molekul air dan partikel tanah
Partikel tanahH2O
Adesi Kohesi
Air terikat Air bebas 43
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Air Tersedia untuk pertumbuhan tanaman
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Status Air Tanah
Perubahan status air dalam tanah, mulai dari kondisi jenuh hingga titik layu
Jenuh Kap. Lapang Titik layu
100g 8g udara
Padatan Pori
100g 20g udara
100g 10 g udara
100g air 40g tanah jenuh air
kapasitas lapang
koefisien layu
koefisien higroskopis 45
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TEGANGAN &
KADAR AIR
PERHATIKANLAH proses yang terjadi kalau tanah basah dibiarkan mengering. Bagan berikut melukiskan hubungan antara tebal lapisan air di sekeliling partikel tanah dengan tegangan air
Bidang singgung tanah dan air Koef. Koef. Kapasitaspadatan tanah higroskopis layu lapang
10.000 atm 31 atm 15 atm 1/3 atm
10.000 atm Mengalir krn gravitasi
Tegangan air
1/3 atm
tebal lapisan air
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JUMLAH AIR DALAM TANAH
The amount of soil water is usually measured in terms of water content as percentage by volume or mass, or as soil water potential. Water
content does not necessarily describe the availability of the water to the plants, nor indicates, how the water moves within the soil profile. The only information provided by water content is the relative amount of
water in the soil.
Soil water potential, which is defined as the energy required to remove water from the soil, does not directly give the amount of water present in the root zone either. Therefore, soil water content and soil water potential
should both be considered when dealing with plant growth and irrigation.
The soil water content and soil water potential are related to each other, and the soil water characteristic curve provides a graphical
representation of this relationship.47
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TEGANGAN vs
kadar air
Kurva tegangan - kadar air tanah bertekstur lempung
Tegangan air, bar
31 Koefisien higroskopis
Koefisien layu
Kapasitas lapang 0.1 Kap. Lapang maksimum
persen air tanah
Air kapilerAir Air tersediahigros-kopis Lambat tersedia Cepat tersedia Air gravitasi
Zone optimum
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Hubungan antara kadar air tanah dan tegangan air tanah untuk tekstur lempung
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STRUKTUR &
CIRI
POLARITASMolekul air mempunyai dua ujung, yaitu ujung oksigen yg elektronegatif dan ujung hidrogen yang elektro-positif.Dalam kondisi cair, molekul-molekul air saling bergandengan membentuk kelompok-kelompok kecil tdk teratur.Ciri polaritas ini menyebabkan plekul air tertarik pada ion-ion elektrostatis. Kation-kation K+, Na+, Ca++ menjadi berhidrasi kalau ada molekul air, membentuk selimut air, ujung negatif melekat kation.Permukaan liat yang bermuatan negatif, menarik ujung positif molekul air.
Kation hidrasi Tebalnya selubung air tgtpd rapat muatan pd per-mukaan kation.
Rapat muatan = Selubung air muatan kation / luas permukaan
50
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STRUKTUR &
CIRI
IKATAN HIDROGEN Atom hidrogen berfungsi sebagai titik penyambung (jembatan) antar molekul air.Ikatan hidrogen inilah yg menyebabkan titik didih dan viskositas air relatif tinggi
KOHESI vs. ADHESIKohesi: ikatan hidrogen antar molekul airAdhesi: ikatan antara molekul air dengan permukaan padatan lainnyaMelalui kedua gaya-gaya ini partikel tanah mampu menahan air dan mengendalikan gerakannya dalam tanah
TEGANGAN PERMUKAAN Terjadinya pada bidang persentuhan air dan udara, gaya kohesi antar molekul air lebih besra daripada adhesi antara air dan udara.
UdaraPermukaan air-udara
air
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ENERGI AIR TANAH
Retensi dan pergerakan air tanah melibatkan energi, yaitu: Energi Potensial, Energi Kinetik dan Energi Elektrik.Selanjutnya status energi dari air disebut ENERGI BEBAS, yang merupakan PENJUMLAHAN dari SEMUA BENTUK ENERGI yang ada.Air bergerak dari zone air berenergi bebas tinggi (tanah basah) menuju zone air berenergi bebas rendah (tanah kering).
Gaya-gaya yg berpengaruhGaya matrik: tarikan padatan tanah (matrik) thd molekul air; Gaya osmotik: tarikan kation-kation terlarut thd molekul airGaya gravitasi: tarikan bumi terhadap molekul air tanah.
Potensial air tanahKetiga gaya tersebut di atas bekerja bersama mempengaruhi energi bebas air tanah, dan selanjutnya menentukan perilaku air tanah, ….. POTENSIAL TOTAL AIR TANAH (PTAT)PTAT adalah jumlah kerja yg harus dilakukan untuk memindahkan secara berlawanan arah sejumlah air murni bebas dari ketinggian tertentu secara isotermik ke posisi tertentu air tanah.PTAT = Pt = perbedaan antara status energi air tanah dan air murni bebas
Pt = Pg + Pm + Po + …………………………
( t = total; g = gravitasi; m = matrik; o = osmotik)
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Hubungan potensial air tanah dengan energi bebas
Energi bebas naik bila air tanah berada pada letak ketinggian yg lebih tinggi dari titik baku pengenal (referensi)
+
0
-
Poten-sial
positif
Poten-sial
negatif
Energi bebas dari air murni Potensial tarikan bumi
Menurun karena pengaruh osmotik
Menurun karena pengaruh matrik
Energi bebas dari air tanah
Potensial osmotik (hisapan)
Potensial matrik (hisapan)
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POTENSIAL AIR TANAH
POTENSIAL TARIKAN BUMI = Potensial gravitasi
Pg = G.hdimana G = percepatan gravitasi, h = tinggi air tanah di atas posisi ketinggian referensi.Potensial gravitasi berperanan penting dalam menghilangkan kelebihan air dari bagian atas zone perakaran setelah hujan lebat atau irigasi
Potensial matrik dan OsmotikPotensial matrik merupakan hasil dari gaya-gaya jerapan dan kapilaritas.Gaya jerapan ditentukan oleh tarikan air oleh padatan tanah dan kation jerapanGaya kapilaritas disebabkan oleh adanya tegangan permukaan air.Potensial matriks selalu negatifPotensial osmotik terdapat pd larutan tanah, disebabkan oleh adanya bahan-bahan terlarut (ionik dan non-ionik).Pengaruh utama potensial osmotik adalah pada serapan air oleh tanaman
Hisapan dan Tegangan Potensial matrik dan osmotik adalah negatif, keduanya bersifat menurunkan energi bebas air tanah. Oleh karena itu seringkali potensial negatif itu disebut HISAPAN atau TEGANGAN.Hisapan atau Tegangan dapat dinyatakan dengan satuan-satuan positif.Jadi padatan-tanah bertanggung jawab atas munculnya HISAPAN atau TEGANGAN.
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Cara Menyatakan
Tegangan Energi
Tegangan: dinyatakan dengan “tinggi (cm) dari satuan kolom air yang bobotnya sama dengan
tegangan tsb”.Tinggi kolom air (cm) tersebut lazimnya dikonversi menjadi logaritma dari sentimeter tinggi kolom air,
selanjutnya disebut pF.
Tinggi unit Logaritma Bar Atmosferkolom air (cm) tinggi kolom air (pF)
10 1 0.01 0.0097 100 2 0.1 0.0967 346 2.53 0.346 1.3 1000 3 110000 4 10 9.674915849 4.18 15.8 1531623 4.5 31.6 31100.000 5 100 96.7492
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KANDUNGAN AIR DAN
TEGANGAN
KURVA ENERGI - LENGAS TANAH Tegangan air menurun secara gradual dengan meningkatnya kadar air tanah.Tanah liat menahan air lebih banyak dibanding tanah pasir pada nilai tegangan air yang samaTanah yang Strukturnya baik mempunyai total pori lebih banyak, shg mampu menahan air lebih banyakPori medium dan mikro lebih kuat menahan air dp pori makro
Tegangan air tanah, Bar 10.000
Liat
Lempung
Pasir
0.0110 Kadar air tanah, % 70
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Tekstur tanah dan air tersedia
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Hubungan antara kadar air tanah dengan tegangan air tanah
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Jelaskan bagaimana tektur tanah mempengaruhi jumlah air tersedia bagi tanaman? Sebanyak 250 kata
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Jelaskan tanah-tanah yang tekturnya halus mampu menahan lebih banyak air dibandingkan dgn tanah-tanah yang teksturnya kasar? Sebanyak 250 kata
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Kapasitas air tersedia dalam tanah yang teksturnya berbeda-beda
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Gerakan Air Tanah
Tidak Jenuh
Gerakan tidak jenuh = gejala kapilaritas = air bergerak dari muka air tanah ke atas melalui pori mikro.Gaya adhesi dan kohesi bekerja aktif pada kolom air (dalam pri mikro), ujung kolom air berbentuk cekung.Perbedaan tegangan air tanah akan menentukan arah gerakan air tanah secara tidak jenuh.
Air bergerak dari daerah dengan tegangan rendah (kadar air tinggi) ke daerah yang tegangannya tinggi (kadar air rendah, kering).Gerakan air ini dapat terjadi ke segala arah dan berlangsung secara terus-menerus.
Pelapisan tanah berpengaruh terhadap gerakan air tanah.Lapisan keras atau lapisan kedap air memperlambat gerakan air Lapisan berpasir menjadi penghalang bagi gerakan air dari lapisan yg bertekstur halus.Gerakan air dlm lapisan berpasir sgt lambat pd tegangan
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Gerakan Jenuh
(Perkolasi)
Air hujan dan irigasi memasuki tanah, menggantikan udara dalam pori makro - medium - mikro. Selanjutnya air bergerak ke bawah melalui proses gerakan jenuh dibawah pengaruh gaya gravitasi dan kapiler.Gerakan air jenuh ke arah bawah ini berlangsung terus selama cukup air dan tidak ada lapisan penghalang
Lempung berpasir Lempung berliat
cm 0
15 mnt 4 jam 30 60
90 1 jam 24 jam
120 24 jam 48 jam
150 30 cm 60 cm Jarak dari tengah-tengah saluran, cm
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Pola Penetrasi dan Pergerakan Air pada tanah Berpasir dan tanah Lempung-liat
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PERKOLASI
Jumlah air perkolasiFaktor yg berpengaruh:
1. Jumlah air yang ditambahkan2. Kemampuan infiltrasi permukaan tanah3. Daya hantar air horison tanah4. Jumlah air yg ditahan profil tanah pd kondisi kapasitas lapang
Keempat faktor di atas ditentukan oleh struktur dan tekstur tanah
Tanah berpasir punya kapasitas ilfiltrasi dan daya hantar air sangat tinggi, kemampuan menahan air rendah, shg perkolasinya mudah dan cepat
Tanah tekstur halus, umumnya perkolasinya rendah dan sangat beragam; faktor lain yg berpengaruh:1. Bahan liat koloidal dpt menyumbat pori mikro & medium2. Liat tipe 2:1 yang mengembang-mengkerut sangat berperan
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LAJU GERAKAN
AIR TANAH
Kecepatan gerakan air dlm tanah dipengaruhi oleh dua faktor:1. Daya dari air yang bergerak2. Hantaran hidraulik = Hantaran kapiler = daya hantar
i = k.fdimana i = volume air yang bergerak; f = daya air yg bergerak dan k = konstante.
Daya air yg bergerak = daya penggerak, ditentukan oleh dua faktor:1. Gaya gravitasi, berpengaruh thd gerak ke bawah2. Selisih tegangan air tanah, ke semua arah
Gerakan air semakin cepat kalau perbedaan tegangan semakin tinggi.
Hantaran hidraulik ditentukan oleh bbrp faktor:1. Ukuran pori tanah2. Besarnya tegangan untuk menahan air
Pada gerakan jenuh, tegangan airnya rendah, shg hantaran hidraulik berbanding lurus dengan ukuran poriPd tanah pasir, penurunan daya hantar lebih jelas kalau terjadi penurunan kandungan air tanahLapisan pasir dlm profil tanah akan menjadi penghalang gerakan air tidak jenuh
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Gerakan air tanah
Gerakan air tanah dipengaruhi oleh kandungan air tanah
Penetrasi air dari tnh basah ke tnh kering(cm) 18
Tanah lembab, kadar air awal 29%
Tanah lembab, kadar air awal 20.2%
Tanah lembab, kadar air awal 15.9%
0 26 156
Jumlah hari kontak, hariSumber: Gardner & Widtsoe, 1921.
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Pengukuran Air Tanah
• Metode Gravimetrik1. Mengukur kandungan massa air (m)2. Take field samples weigh oven dry weigh3. Advantages: accurate; Multiple locations4. Kelemahan: memerlukan tenaga dan waktu
• Metode Perasaan: Feel and appearance1. Take field samples and feel them by hand2. Advantages: low cost; Multiple locations3. Disadvantages: experience required; Not highly
accurate
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• Pencaran neutron (attenuation)– Measures volumetric water content (v)– Attenuation of high-energy neutrons by hydrogen nucleus– Advantages:
• samples a relatively large soil sphere • repeatedly sample same site and several depths • accurate
– Disadvantages: • high cost instrument • radioactive licensing and safety • not reliable for shallow measurements near the soil surface
• Konstante dielektrik1. A soil’s dielectric constant is dependent on soil moisture2. Time domain reflectometry (TDR)3. Frequency domain reflectometry (FDR)4. Primarily used for research purposes at this time
Pengukuran Air Tanah
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Pengukuran Air Tanah: Neutron Attenuation
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• Tensiometer– Measure soil water potential (tension)– Practical operating range is about 0 to 0.75 bar of tension
(this can be a limitation on medium- and fine-textured soils)
• Electrical resistance blocks– Measure soil water potential (tension)– Tend to work better at higher tensions (lower water
contents)
• Thermal dissipation blocks– Measure soil water potential (tension)– Require individual calibration
Pengukuran Air Tanah
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Tensiometer untuk mengukur potensial air tanah
Porous Ceramic Tip
Vacuum Gauge (0-100 centibar)
Water Reservoir
Variable Tube Length (12 in- 48 in) Based on Root Zone Depth
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Electrical Resistance Blocks & Meters