Join Date: Jun 2011
Location: Dorset, SW England, UK
What is CEC?
What is CEC?
The Exchange Capacity of soil and growing mediums is a measure of its ability to hold and release various chemical elements and compounds that include nutrients for plant growth.
If you study chemistry you will learn that elements and compounds are ions, which means a charged particle. These particle ions can either be positively charged or negatively charged. Positive charged ions are called cations, and negatively charged ions are called anions.
Positive charged ions are attracted to the surface of a negatively charged medium and held there in a condensed layer where they may come into contact with plant roots. This “holding” prevents the cations from leeching out of the medium.
In agriculture a soil low in CEC would have its nutrients washed and carried away every time it rained. In the aquarium a low CEC substrate would have its nutrients leech into the water column.
Positive charged cations
Cations include some macro nutrients and all trace mineral nutrients. Other macro nutrients are anions. The most critical nutrients for CEC are Calcium, Magnesium, Potassium, Sodium, and trace minerals including iron.
Soil Organic Matter
Soil organic matter is the chief component of top soils and potting soil. This is decomposed organic material from compost, manure and humus. SOM is both positively charged and negatively charged so it will attract both cations and anions. Clay particles are almost always positively charged and attract only cations.
Cation Exchange Capacity is the measure of how many negatively charged sites are available in the soil or medium. Clay and other inert materials will continue their CEC indefinitely while SOM will last only until the organic material breaks down from further decomposition.
Please also add CFL (Compact Fluorescent Lamp) to the list - I had to Google that too.
Last edited by sewingalot; 07-21-2012 at 08:23 PM.
Reason: removed dead link