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Hydroponics Cation & Anion Exchange Capabilities (intro.)!

© a.k.a. MBR

One of the great mysteries of the universe that has been elucidated by modern-day chemists, horticulturists, and other scientists is the wondrous intrinsic capability that certain compounds exhibit which allows them to adsorb (that's right, aDsorb!) other ions and molecules onto their surfaces. In an agricultural context, this allows for a greater understanding of the processes by which nutrients are stored and distributed in rhizobial regions (around the roots).

Adsorption is basically defined as the physical attraction between two separate bodies, allowing for one body to be held on the other's surface, kind of like the way a balloon will stick to a wall after you rub it on something hairy, like a cat or dog. This attraction technically involves electrical (electrostatic) charges and magnetic fields, etc. and is quantified according to charge capacity. Different types of soils and natural or synthetically produced soil-less plant growth media constituents (like clays, organic matter, zeolites, etc.) can have a net positive or negative charge on their surface due to differential ionic substitution during their formation making them colloidal. These charges allow for the substances to gather a certain amount of complementary and oppositely charged particles on their surfaces. Without getting into the sub-atomic nuclear physical relationships between the quarks and neutrinos involved, depending on the pH (acidity or alkalinity) of the sample, the net charge available can vary a great deal due to variations in ionic concentrations.

A Cation is defined as a positively charged ion (in solution for our purposes), such as Calcium (Ca2+), Potassium (K+), Magnesium (Mg2+), et cetera.

An Anion is defined as an ion that has an overall negative charge, examples being Sulph(f)ates, Phosphates, and the like.

Thus, the acronyms CEC & AEC were coined for Cation Exchange Capability and Anion Exchange Capability respectively in order to describe the relative levels of attractive forces attributable to samples with differing charge types.

For more info, please visit these juicy web sites:

http://www.agronomy.psu.edu/Courses/SOIL...

http://soils.ag.uidaho.edu/soils205/note...

http://syllabus.syr.edu/esf/rdbriggs/for...

http://www.gsaresources.com/cationexchan...

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