soil acidity and ph

Soil Acidity and pH

Causes, remediation, and implications

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KEMASAMAN TANAH & pH

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The relationship between pH, pOH, and the concentrations of hydrogen and hydroxyl ions in water solution


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)


http://www.traylorchemical.com/images/faqs/phchart.jpg

Most nutrients are highest and most toxins are lower at pH 5.5-7


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.


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


http://www.biconet.com/testing/GIFs/st-t2.jpghttp://img.alibaba.com/photo/51008043/Soil_pH_Meter.jpg

Methods for measuring soil pH


Kemasaman CadanganExchangeable or KCl-extractable acidity [(Al+3 + H+) /

CEC]Mostly Al+3 on clay mineral sitesOrganic acid groups:

RCOOH = RCOO- + H+

Residual or non-exchangeable acidity (H+ and Al+3 not displaced by KCl or salt solution):

SOM-Al complexesSolid phase Al+3 + H+ in soil minerals


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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


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+


Bahan Organik

Organic acid groups deprotonate:RCOOH = RCOO- + H+

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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


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


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.


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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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)


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


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)


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


As CO2 concentration

increases, proton (H+) production

increases and pH decreases

Soda pop or carbonated

beverages have pH 3 - 4


Hidrolisis Logam1. Polyvalent metals go through several hydrolysis

steps releasing protons 2. Alum (KAl(SO4)2) is a commercial product for

lowering pH

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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+


• 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


Peningkatan pH Tanah

Bahan Kapur

1. CaCO3 calcic limestone2. 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


• 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


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


soil acidity and ph

Documents

ph soil acidity

soil chem

ph causes

pptkemasaman tanah ph

metal toxicity

water solutionsumber

hydroxyl ions

concentrations of hydrogen