Cation Exchange Capacity

Understanding Cation Exchange Capacity

One of the chemical properties of the soil are closely associated with the availability of nutrients to plants and soil fertility is an indicator of Cation Exchange Capacity ( CEC ) or Cation Exchangable Cappacity ( CEC ) . CEC is the total amount of exchangeable cations (cation exchangable ) on the surface of the negatively charged colloid . CEC is a unit of measurement results milliequivalen cations in the soil or to 100 grams per 100 g of soil cations .

Some terms CEC

Based on the type of colloid is negatively charged surface , CEC can be grouped into three , namely :
1 . CEC inorganic colloids or clay soil known as CEC ,
2 . CEC organic colloids known as CEC or soil organic matter , and
3 . Total CEC or CEC .

CEC CEC or clay Inorganic Colloids

CEC clay is the amount of exchangeable cations on the surface of inorganic colloids ( colloidal clay ) which are negatively charged .
Clay CEC value depends on the type of clay , for example :
a. Kaolinite clay CEC value = 3 s / d 5 me/100 g .
b . Clay and Clay Chlorite Illit , has a value of CEC = 10 s / d 40 me/100 g .
c . Montmorillonite clay , CEC value = 80 s / d 150 me/100 g .
d . Vermikullit clay , CEC value = 100 s / d 150 me/100 g .

CEC Organic Colloids

CEC organic colloids often referred to as CEC of soil organic matter is the amount of exchangeable cations on the surface of negatively charged organic colloids .
Organic colloids CEC value is higher than the value of the colloidal inorganic CEC . CEC value of organic colloids ranged from 200 g to 300 me/100 me/100 g .

The total CEC or CEC Land

A total CEC CEC value of the soil is the total amount of exchangeable cations from the soil , either cations on the surface of colloidal organic ( humus ) and cations on the surface of inorganic colloids ( clay ) .


Differences CEC Land Based Sources Negative Charge

Based on the negative charge of land resources , soil CEC values ​​are divided into 2 , namely :
1 . CEC permanent charge , and
2 . CEC is not a permanent charge .


Permanent Load CEC

Permanent charge CEC is the sum of exchangeable cations on the surface of colloidal clay with a negative charge originating source of isomorphic substitution mechanism . Isomorphic substitution is the replacement mechanism between the position of the cation with the size or diameter of the cation is almost the same but different content. The isomorphic substitution occurs from high divalent cations with lower valence cations in the structure of the clay plates , both plates clay Si - Al - tetrahedron and octahedron .

Examples of the negative charge above events are : ( a) . isomorphic substitution of Si position with 4 + charge on the clay plate structure by Si - tetrahedron charged Al 3 + , resulting in an excess of negative charge , ( b ) . the isomorphic substitution of Al positions are charged 3 + on clay Al - octahedron structure by Mg 2 + -charged , also occurred one negative charge , and ( c ) . isomorphic substitution of the position of the Al 3 + -charged isomorphic substitution of previous results on Si - tetrahedron clay plates that have been charged neatif one , was replaced by Mg 2 + -charged , then it happens again the addition of a negative charge , thus forming a negative charge on the two plates the Si - tetrahedron clay . The negative charge is formed is not affected by changes in soil pH . Measured soil CEC is a permanent charge CEC .


CEC Payload Not Permanent

CEC charge is not permanent or CEC depending on the pH of the soil is the sum of exchangeable cations on the surface of colloidal clay with a source of negative charge of clay is not derived from the mechanisms of substitution isomorphic but derived from the mechanism of fracture or pop-up on the surface of colloidal clay , so it depends on the concentration of H + and OH - from the soil solution .


Soil CEC Measurement Results

Based on the measurement and calculation techniques in the laboratory soil CEC , the CEC values ​​are grouped into two , namely :
1 . Effective CEC
2 . The total CEC .