soil acidity and ph causes, remediation, and implications sumber:...
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Soil Acidity and pH
Causes, remediation, and implications
Sumber: cahe.nmsu.edu/directory/.../Powerpoint/14%20Nov%20soil%20chem.ppt
KEMASAMAN TANAH & pH
http://www.msichicago.org/ed/learninglabs/imgs/waters_ph_chart.jpgSumber: cahe.nmsu.edu/directory/.../Powerpoint/14%20Nov%20soil%20chem.ppt
The relationship between pH, pOH, and the concentrations of hydrogen and hydroxyl ions in water solution
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pH is a ‘master’ variable
1. affects chemical, physical, and biological properties of soils
2. Nutrient availability (optimum pH for most crops is 5.5 - 7)
3. Metal toxicity and solubility e.g., Al toxicity at pH <5.5 (also Mn solubility and toxicity)
4. Microbial activity (especially important in the N cycle)
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http://www.traylorchemical.com/images/faqs/phchart.jpg
Most nutrients are highest and most toxins are lower at pH 5.5-7
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Relationships existing in mineral soils between pH
and the availability of plant nutrients.
A pH range of about 5.5 to 7.0 seems to be best to
promote the availability of plant nutrients. In short, if
the soil pH is suitably adjusted for phosphorus,
the other plant nutrients, if present in adequate
amounts, will be satisfactorily available in
most cases.
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Kemasaman Aktif
acidity that is in solution(H+) that is measured with a pH ‘specific ion’ electrode (best), color indicators, dyes, litmus papers.
Includes Al+3 in solution that hydrolyzes to form H+ and Al(OH)x species
Relatively speaking, active acidity is only a small amount compared to reserve acidity
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http://www.biconet.com/testing/GIFs/st-t2.jpghttp://img.alibaba.com/photo/51008043/Soil_pH_Meter.jpg
Methods for measuring soil pH
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Kemasaman Cadangan
Exchangeable or KCl-extractable acidity [(Al+3 + H+) / CEC]
Mostly Al+3 on clay mineral sites
Organic acid groups:
RCOOH = RCOO- + H+
Residual or non-exchangeable acidity (H+ and Al+3 not displaced by KCl or salt solution):
SOM-Al complexes
Solid phase Al+3 + H+ in soil minerals
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http://hubcap.clemson.edu/~blpprt/acid_photos/Buffering2.jpgSumber: cahe.nmsu.edu/directory/.../Powerpoint/14%20Nov%20soil%20chem.ppt
http://www.landfood.ubc.ca/soil200/images/15_3acidity.jpgSumber: cahe.nmsu.edu/directory/.../Powerpoint/14%20Nov%20soil%20chem.ppt
http://www.landfood.ubc.ca/soil200/interaction/acidity.htmSumber: cahe.nmsu.edu/directory/.../Powerpoint/14%20Nov%20soil%20chem.ppt
Perubahan pH tanah (Alamiah dan Buatan)
• Management dan land use– Fertilizers, organic matter, and other amendments– Submergence and subsequent uplift of land exposing
reduced sediments to oxidation processes • Pencemaran
– Acid rain– Mining
• Iklim– Weathering and leaching– Rainfall leaching– Plant growth: uptake of cations and release of protons
• Hidrolisis Logam
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Pupuk dapat menurunkan pH tanah
• Oxidation of Ammonium, or ‘Nitrification’
NH4+ + 2O2 NO3
- + H2O + 2H+
• Phosphate fertilizers:
Triple superphosphate hydroxyapatite + H+
Ca(H2PO4)2 Ca5OH(PO4)3 + H+
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Bahan Organik
Organic acid groups deprotonate:
RCOOH = RCOO- + H+
http://www.rsc.org/ej/gt/2000/b001869o/b001869o-f3.gifSumber: cahe.nmsu.edu/directory/.../Powerpoint/14%20Nov%20soil%20chem.ppt
Bahan Amendment yg menurunkan pH tanah
Oxidation of elemental sulfur produces sulfuric acid which
dissociates easily
S0 + 3/2O2 + H2O H2SO4
Some growers even use sulfuric acid – but it is very dangerous,
expensive, and doesn’t last long in arid zone soils
Alum, KAl(SO4)2 is a commercial product for lowering pH
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http://www.latrobe.edu.au/envsci/assets/images/publicity/amd2-edit.jpg
http://web.missouri.edu/~umcsnrsoilwww/290_2003/images/gillpic1.gif
Acid sulfate soilsDredging waterways, draining swamps, spoil piles, mine tailings
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Iron staining is often a good indicator of disturbed acid sulfate soils.
When acid sulfate soils are disturbed and undergo oxidization, the sulfuric acid produced mobilizes iron,
aluminum and heavy metals present in the soil.
Toxic amounts of dissolved iron can then be washed into waterways.
This iron can precipitate when in contact with less acid water, such as rainwater or seawater.
This results in a rust-colored iron oxide scum or ‘floc' which
can smother vegetation and stain concrete and soil.
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Hujan Asam
1. Oxidation of sulfur (SO2) in coal (power plants) and NOx (car exhaust) to sulfuric and nitric acid
2. pH 4-5 (pure rainfall = pH 5.6) 3. Extensive in heavily populated areas with
heavy rainfall (soils already slightly acid)4. Recent regulations have improved some
conditions.5. Lakes and forests impacted, low buffering
capacity
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http://www.maine.gov/dep/air/acidrain/images/ARAIN1.jpgSumber: cahe.nmsu.edu/directory/.../Powerpoint/14%20Nov%20soil%20chem.ppt
http://www.newsroom.ucr.edu/releases/images/257_3.gifSumber: cahe.nmsu.edu/directory/.../Powerpoint/14%20Nov%20soil%20chem.ppt
Oksidasi Sulfida
FeS2 + H2O + O2 4H+ + 2SO4-2 + Fe(OH)3
Most metal ores are in sulfide form (ZnS, PbS, CuS, etc) that oxidizes when exposed to air in tailings piles once exhumed from below ground.
Same concept as exposed submerged soil in coastal zones (acid sulfate soils)
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http://www.agf.gov.bc.ca/clad/britannia/images/acid_mine_fig1.jpgSumber: cahe.nmsu.edu/directory/.../Powerpoint/14%20Nov%20soil%20chem.ppt
Acid mine drainage
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Efek Iklim
• Excessive rainfall: Leaching of cations through the soil profile by rain, weathering of the soil– Carbonation; hydrolysis; hydration…
• Excessive irrigation: unlikely cause of acidity since most irrigation occurs in arid or semi-arid regions with accumulated salts, carbonates, etc (buffer pH)– Most irrigated regions are neutral to alkaline (they are
irrigated because there isn’t enough rain to support crops, therefore the salts and cations don’t leach out of soils)
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Pembentukan Asam Karbonat
• forms in rainwater or soil water
CO2 + H2O H2CO3
H2CO3 H+ + HCO3-
----------------------------
CO2 + H2O H+ + HCO3-
• [CO2] is higher in soils than aboveground
• Most unpolluted rainfall is slightly acidic
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As CO2 concentration
increases, proton (H+) production
increases and pH decreases
Soda pop or carbonated
beverages have pH 3 - 4
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Hidrolisis Logam
1. Polyvalent metals go through several hydrolysis steps releasing protons
2. Alum (KAl(SO4)2) is a commercial product for lowering pH
http://www.wou.edu/las/physci/ch412/hydrxn2.jpgSumber: cahe.nmsu.edu/directory/.../Powerpoint/14%20Nov%20soil%20chem.ppt
Hydrolysis of Al+3
H2O OH- + H+
Al+3 + H2O Al(OH)+2 + H+
Al(OH)2+ + H2O Al(OH)2+1 + H+
Al(OH)2+1 + H2O Al(OH)3 + H+
Al(OH)3 + H2O Al(OH)4-1 + H+
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• Burning plant residues or adding ashes– Wood ashes are a source of K, Ca, Mg CO3’s
• Liming materials (pure calcium carbonate or dolomitic lime) will increase soil pH.– Lime is a certified organic product – Slow-release product. Do not add every year. – 15-25 lbs lime per 1000 sq ft is recommended
• Gypsum is calcium sulfate. – It is not a substitute for lime, and has very little effect on
soil pH. Gypsum only improves structure in soils that have extremely high sodium contents
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Peningkatan pH Tanah
Bahan Kapur
1. CaCO3 calcic limestone
2. CaMg(CO3)2 Dolomite3. CaO: Quick lime4. Byproducts: ground shells, cement
factory5. Gypsum is NOT a liming material, as it
has very slight effect on pH, but can provide Ca as a nutrient or exchange with Na
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• Karakteristik Kapur– cost – purity – speed of effect (fine ground vs coarse) – ease of handling
• Kebutuhan Kapur– depends on pH, CEC and buffer capacity of the
soil
• Aplikasi apur: small amounts split and incorporated into the soil
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Pengapuran untuk menaikkan pH Tanah
http://wwwlb.aub.edu.lb/~webeco/SIM215acidsoilsandlimimg_files/image002.gif
Untuk menaikkan pH dari 6 menjadi 7 memerlukan lebih banyak kapur, dibandingkan dengan kenaikkan pH dari 4 menjadi 5
Sumber: cahe.nmsu.edu/directory/.../Powerpoint/14%20Nov%20soil%20chem.ppt
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