bahan kajian mk. dasar ilmu tanah
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Bahan Kajian MK. Dasar Ilmu Tanah. REAKSI PERTUKARAN ION & KETERSEDIAAN HARA. Smno.agroekotek.fpub.okt2013. Muatan listrik pd Komponen Tanah. Humus » 200 cmol c /kg Smectite /Vermiculite » 100 cmol c /kg Illite » 25 cmol c /kg Kaolinite » 10 cmol c /kg - PowerPoint PPT PresentationTRANSCRIPT
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Bahan Kajian MK. Dasar Ilmu Tanah
Smno.agroekotek.fpub.okt2013
REAKSI PERTUKARAN
ION &
KETERSEDIAAN HARA
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• Humus » 200 cmolc/kg
• Smectite/Vermiculite » 100 cmolc /kg
• Illite » 25 cmolc /kg
• Kaolinite » 10 cmolc /kg
• Fe and Al oxides » 5 cmolc /kg
Muatan listrik pd Komponen Tanah
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ColloidNegativecharge
Positivecharge % constant % variable
Humus 200 0 10 90Vermiculite 120 0 95 5Smectite 100 0 95 5Illite 40 0 80 20Kaolinite 12 4 5 95Fe & Al Oxides 5 5 0 100
Asalnya Muatan Listrik
cmol / Kg
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Penjerapan Ion
Muatan negatif pada partikel tanah
dinetralkan oleh anion dari larutan tanah
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Kation Yang Dijerap (Kation-Tukar)
(a) arid region soils = "basic" cations Ca2+, Mg2+, K+, Na+
(b) humid region soils = “acidic” cations as well
Ca2+, Mg2+, H+ and Al3+
(c) Kekuatan Jerapan Al3+> Ca2+ = Mg2+ > K+ = NH4
+ > Na+
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Pertukaran Kation
Exchange process Ca2+-colloid + 2 Na+ ¬¾® 2 Na+-colloid + Ca2+
= Na+ replaces Ca+2 adsorbed to soil colloids
Ca-x + 2 Na+ ¬¾® 2 Na-X + Ca2+
X = the soil solid phase
Dispersion
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Saline Soils
EC > 4 ds/m = osmotic stress
* salt sensitive plants (EC = 2 ds/m) 3 bean, onion, potato, raspberry, carrot,
dogwood, larch, linden, peach, rose, tomato
* salt tolerant plants (EC = 10 ds/m) 3 sugarbeets, barley, cotton, rosemary,
wheat grass, wild rye
(see table 10.2 - 13th ed. or 10.3 – 12th ed.)
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Sodic Soils (ESP > 15)
flocculation
poorwater
infiltrationdispersion
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Sodium Ion Effect
flocculation dispersion
è attraction ç
Ca2+ & Mg2+
ç repulsion è
Na+
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SAR Parameter
SAR is measured ESP/ESR is estimated in water or extract for soil solids
ESR = 0.015(SAR) - 0.01
Good quality irrigation water: 4 for salt hazard = EC < 2 ds/m 4 for Na+ hazard = SAR < 15
Predict sodium effect from saturated soil extract or irrigation water
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Sources of Acidity
á Water: H2O ¬® H+ + OH-
á CO2 from soil respiration CO2 + H2O ¬® H2CO3 ¬® H+ + HCO3
-
carbonic acid
á Organic acids from O.M. decomposition RH ¬® R- + H+
á Oxidation of S and N S ¾® H2SO4 ¾® 2 H+ + SO4
2-
NH3 ¾® HNO3 ¾® H+ + NO3-
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Human-Induced Acidity
* Chemical fertilizers ü ammonium-based N materials
NH4+ ¾(O2)® HNO3
ü Ferrous-Fe materials
Fe2+ ® Fe3+ ¬(+ 3 H2O)® Fe(OH)3 + 3 H+
ü Elemental Sulfur 2 So + 3 O2 + 2 H2O ¾® 4 H+ + 2 SO4
2-
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ü Acid Rain: N and S gases emitted from combustion processes SO2 ¾(O2, H2O)® H2SO4
NOx ¾(O2, H2O)® HNO3
mining wastes, wetland drainage
- oxidation of sulfide (S2-) mineral
S2- ¾(O2, H2O)® H2SO4
Human-Induced Acidity
http://www.physicalgeography.net/fundamentals/8h.html
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Phases of Soil Acidity
bound acidity exchangeable acidity soluble acidity
As acidity is removed from or added to soil solution Ø maintain equilibrium within system Ø must change all forms to change pH
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Acid Soils: Role of Aluminum
Al3+ ¨ Al(OH)2+ ¨ Al(OH)2+ ¨ Al(OH)3
|¬ strongly ¾®|¬ moderately ¾¾¾®|¬ alkaline acid soils acid soils soils
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Al3+ + H2O Al(OH)2+ + H+
K = 10-4.93
Al(OH)2
+ + H2O Al(OH)2+ + H+
K = 10-4.97
Al(OH)2+ + H2O Al(OH)3
o + H+
K = 10-5.7
Al(OH)3o + H2O Al(OH)4
- + H+
K = 10-7.4
Acid Soils: Role of Aluminum
http://www.landfood.ubc.ca/soil200/interaction/acidity.htm
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Al+3 ¨ Al(OH)+2 ¨ Al(OH)2+ ¨ Al(OH)3
Changes in Al Speciation
- - - - - -
- - - - - -
Clay Interlayer Soil Solution
pH 4 pH 6
H+
H+
Why [Al3+] ~ [H+] in Acid Soils
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Fe3+ + H2O <--> Fe(OH)2+ + H+ K = 10-2.19
Fe(OH)2
+ + H2O <--> Fe(OH)2+ + H+ K = 10-3.5
Fe(OH)2+ + H2O <--> Fe(OH)3
o + H+ K = 10-7.4
Fe(OH)3
o + H2O <--> Fe(OH)4- + H+ K = 10-8.5
Why Not Iron?
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Liming Materials
Carbonate forms(a) "limestone" deposits and
industrial byproducts
(b) calcite = (CaCO3) = calcium carbonate and
dolomite = CaMg(CO3)2
(c) dolomitic limestone maintains Ca:Mg balance
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Liming Materials
Oxide and Hydroxide forms(a) oxides formed by heating limestones
CaCO3 ¾(heat)® CaO + CO2calcite gas
burned lime or quicklime
(b) add water to oxides to form hydroxides CaO + H2O ¾® Ca(OH)2
hydrated lime
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Reaksi Kapur dalam Tanah1. Neutralize acidity
2 H-X + CaCO3 ¾® Ca-X + H2CO3 + H2O
2. Base Saturation increases
BS = (CEC – [Al3+][H+]) / (CEC) * 100
BS = {[Na]+[K]+[Ca]+[Mg]}/CEC *100
3. Soil pH increases
4. Al solubility decreases Al+3 + 3 OH- ¾® Al(OH)3
soluble insoluble (toxic) (not toxic)
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Ciri-ciri Tanah Masam
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Wetland (Hydric) Soilsand
Redox Conditions
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CH2O
CO2
O2
H2O
NO3-CH2O
CO2 N2
Fe(OH)3CH2O
CO2 Fe2+
CH2O
CO2
SO42-
H2S
Energy YieldsDonor Acceptor
700
400
100
Eh (mV)* Condition
oxic
suboxic
anoxic
*pH 7
MnO2CH2O
CO2 Mn2+
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Soil Colors
Yellow -> Orange -> Red Fe(III) minerals
Black (veneer) Mn(IV) minerals
Dark Brown (disseminated) Organic Matter
Aerobic Environments
Gray -> Green -> Black Fe(II) minerals
Dark Brown (disseminated) Organic Matter
Anaerobic Environments
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Iron massesRedox depletions
Root linings
MottlingNodules
Gleyed colors
Redoximorphic Features
Histic Horizons
“Rotten Eggs”
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Plant Effects on Redox Conditions
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FeIII(OH)3
deposit
O2(g)
Pembentukan Plaque pada Akar Tanaman
Fe(OH)3
O2
H2O
Fe2+