Download - Bahan Kajian MK. Dasar Ilmu Tanah
Bahan Kajian MK. Dasar Ilmu Tanah
Smno.agroekotek.fpub.okt2013
REAKSI PERTUKARAN
ION &
KETERSEDIAAN HARA
• 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
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
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+
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
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.)
Sodic Soils (ESP > 15)
flocculation
poorwater
infiltrationdispersion
Sodium Ion Effect
flocculation dispersion
è attraction ç
Ca2+ & Mg2+
ç repulsion è
Na+
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
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-
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-
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
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
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
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
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
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?
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
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
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)
Ciri-ciri Tanah Masam
Wetland (Hydric) Soilsand
Redox Conditions
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+
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
Iron massesRedox depletions
Root linings
MottlingNodules
Gleyed colors
Redoximorphic Features
Histic Horizons
“Rotten Eggs”
Plant Effects on Redox Conditions
FeIII(OH)3
deposit
O2(g)
Pembentukan Plaque pada Akar Tanaman
Fe(OH)3
O2
H2O
Fe2+