Sumber : classes.uleth.ca/200801/geog3080a/ SOILS %20PART%20V%202008. ppt

Sumber: classes.uleth.ca/200801/geog3080a/SOILS%20PART%20V%202008.ppt

KEMASAMAN TANAH

&Permasalahannya

1. Asam KarbonatCarbon dioxide gas from soil air dissolves in waterRoot respiration and soil decomposition provide extra CO2

CO2 + H2O H2CO3 HCO3- + H+

2. Asam-asam dari Metabolism BiologisMicrobes break down organic matter, producing organicacids such as citric acid, carboxylic acids and phenolic acids

RCH2OH… + O2 + H2O RCOOH RCOO- + H+

3. Akumulasi Bahan Organik(i) Loss of cations by leaching due to soluble humic complexes combining with non-acid nutrient cations (eg. Ca2+)(ii) Organic matter is a source of H+ ionsSumber: classes.uleth.ca/200801/geog3080a/SOILS%20PART%20V%202008.ppt

Proses-proses Pengasaman Tanah

4. Oksidasi Nitrogen (Nitrification)Nitrogen memasuki tanah sebagai NH4

+

Diubah menjadi asam nitrat .

NH4+ + 2O2 H2O + H+ + H+ + NO3

-

5. Oksidasi Sulphur6. Asam-asam dalam air hujan

H2SO4 SO42- + 2H+

HNO3 NO3- + H+

7. Plant Uptake of CationsPlants exude H+ ions or take up anions (eg. SO4

2-) tobalance off cation uptake


Proses-proses Pengasaman Tanah

Kation H+ yang dijerap pada permukaan liat dapat merusak struktur mineral dan melepaskan Al3+ dalam prosesnya

Aluminium sangat toksik bagi kebanyakan jenis tanaman

Al memacu hidrolisis H2O

Al bergabung dnegan OH-, meninggalkan H+ dalam larutan tanah

Tolerant plants secrete organic acids into the soil around the root. Organic acids such as (eg. malate or citrate) are able to chelate the Al that is in the soil solution near the root tip. Al that is bound to organic acids cannot enter the plant root.


Toksisitas Al.

1. Acids are neutralized in soils with available bases2. Canadian Shield severely affected in central and eastern Canada


H+ + HSO3-

SO2 SO3

sun

O2

H2SO4 2H+ + SO4

2-

H+ + NO3-

2N20 + O24NO

H2O

4NO2 2HNO3 + 2HNO2

2O2 2H2O


• Weathering of non-acid cations from minerals An example is the weathering of calcium from silicates

Ca-silicate + 2H+ H4SiO4 + Ca2+

• Soil maintains its alkalinity if the release of cations from weathering minerals exceeds leaching losses

• Tanah-tanah masam berkembang pada kondisi:

(i) Lingkungan dengan curah hujan tinggi(ii) Bahan induk miskin Ca, Mg, K , Na(iii) where there is a high degree of biological

activity, resulting in H2CO3 formation


Kepekaan terhadap Pengasaman

Efek pH tanahTerhadap KTK

KTK meningkat dengan pH karena:

(i) Binding and release ofH+ ions on pH-dependent charge sites

(ii) Hydrolysis reactionsinvolving Al


Persen Kejenuhan Basa (KB)

= cmol of exchangeable Ca2+ + Mg2+ + K+ + Na+

cmolc of CEC

= 100 – persen kejenuhan asam.Note: Percent acid saturation, though less often cited, is determined by cmolc Al3+ & H+ ions divided by cmolc of CEC. This is actually moremeaningful, because Ca, Mg, K and Na ions are not true bases!


1. Soils with high clay or organic content tend to have the highest buffering capacity

2. Why? Importance of exchangeable and residual acidity

Contoh Proses Penyangga:(i) Aluminium hydrolysis (in very acid soils)

Al(OH)2+ + H2O Al(OH)3 + H+

Adding more H+ ions will drive the reaction to the left.


Proses-proses Penyangga dalam tanah

(ii) Protonation and deprotonation of organic matter

H+ ions dissociate when a base is added, preventingpH from rising as much as expected.

CEC increases as the H+ ions are removed, increasingthe negative charges

(iii) pH-dependent charge sites in clays

Again, adding a base dissociates H+ ions from hydroxylgroups and oxygen atoms

(iv) Cation exchange

As H+ ions are added, most end up attracted to negative charge sites so that pH changes less than expected. If abase is added, they are replaced by H+ ions or Al ionsfrom exchange sites. (most effective when pH>6).

(v) Carbonate dissolution and precipitation (Eq. 9.18)



LimingLime reacts with CO2 and H2O, to produce bicarbonate (HCO3

-)

Example:CO3

- + 2H+ CO2 + H2O

CaMg(CO3)2 + 2H2O + 2CO2 Ca2+ + 2HCO3- + Mg2+ + 2HCO3

-

•Bicarbonate is reactive with exchangeable and residual soil acidity

•Ca2+ and Mg2+ replace H+ and Al3+ on clay colloids

H+ Soil Colloid + CaCO3 Soil Colloid-Ca++ + H2O + CO2

H+


PENGAPURAN


Proses-proses yang mempengaruhi pH tanah


Efek Pengapuran terhadap pH tanah

Efek pH tanah terhadap kandungan Hara dan Mikroba Tanah


(i) Metode Zat PewarnaCertain organic compounds change colour inresponse to pHDrops of dye solution can be placed on white spot plate (in contact with soil)

(ii) Metode PotentiometrikDifference between H+ ion activity in soil suspension and glass electrode gives pH


Penentuan pH tanah

Sumber : classes.uleth.ca/200801/geog3080a/ SOILS %20PART%20V%202008. ppt

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