Skip to main content

Understanding the Importance of Cation Exchange Capacity


I was recently asked to provide a simplified explanation on the importance of Cation Exchange Capacity (CEC) values.


My Response: 
  • CEC is the ability of a soil to hold onto plant nutrients.  
  • The finer the particle size the higher CEC value, generally speaking. For example sand particles are course and visible to the naked eye, where as clay particles are fine and are not visible to the naked eye. So clay will have a higher CEC value than sand. It is obvious to most of us that sand cannot hold onto water or nutrients as well as a soil with a finer texture. Therefore, soils rich in Clay and Loam size particles are universally recognized as being better for farming - CEC explains this. 
  • The numerical value for CEC represents how much nutrition can be held by a given amount of soil. For example one pound of a clay loam soil with a CEC value of 20 will hold 4 times as many nutrients as a sandy soil with a CEC value of 5. 20/4 = 5. 
  • It's all about math, for example Nitrogen in a cation form (not all nitrogen fertilizers are in a cation form) can be stored in a soil. Here is a simplified calculation - A CEC value of 20 can hold 200 pounds of cation nitrogen, 200/20 = 10. Where a sand with a CEC value of 5 can only hold 50 pounds of cation nitrogen,  50/5 = 10.  
  • Well decomposed organic matter may have a higher CEC value than sand or clay, but it is insignificant when organic matter represents a tiny percentage of the soil.  See the attached chart on the potential CEC values of various substances!  For example, if your soil is only 1% organic matter it does not contribute significantly to CEC values, when compared to the massive volume of the soil itself.  This is often called the buffering capacity of the soil and is also related to any attempt to change the pH of the soil!   On the chart you will notice that Humus and the organic matter of compost are not the same thing, as Humus is referring to the recalcitrant (persistent and resistant to decay) soil carbon substances that are powerful biologic chemicals containing the active ingredient of Humic Acids.  These substances have a huge CEC value and are very significant when it comes to plant nutrient availability.   If the Humic Acid is Supramolecular, the molecules are capable of amazing characteristics, including how they perform as a CEC factor.    The best way to increase CEC is to increase Humic Acid levels in your soil. This is good because Humic Acids are part of the recalcitrant soil carbon pool, which is resistant to decay; meaning Humic Acids are capable of lasting thousands of years in an undisturbed soil. Where as organic matter is labile carbon, which is subject to rapid changes; because labile carbons are unstable they decay easily and disappear from the soil quickly. 
  • CEC may be the limiting factor for having a fertile soil.  In order to improve the fertility of your soil when CEC is limiting you, add Humic Acids as the most effective tool.  However, don't be fooled by "New and Improved" formulations of Humic Acids that claim you only need a few gallons or pounds per acre, as that's not how the math works and CEC and the ability to hold onto the hundreds of pounds of nutrients needed by a crop is all about math.  


Please leave comments!



    Comments

    Post a Comment

    Popular posts from this blog

    Soil Health: Level 2 - Description of Terms (Carbon Compounds)

    The  Labile Carbon  is also known as the 'Rapid Cycling Carbon' and its composed of all the Soil Organic Matter that is dead and actively decomposing.  It's benefit to the soil is that it provides a source for minerals that are being recycled as potential plant nutrients, so in a sense it's Nature's fertilizer.  Active Carbon   also known as Reactive Carbon is more complex than the Labile Carbon in that its composed of all the dead and actively decomposing organic matter plus all the living soil microbial community that will eventually die and begin decomposing.   For example, the hyphae of mycorrhizae only live about 5 to 7 days before they die and start to decompose, while the fungus organism itself may live far longer.  Recalcitrant Carbons   are the Humic substances made up of complex organic chemistry, some of which is inert and some of which is very reactive and are powerful biologics, such as the Humic Acids.  Recalcitran...
    9 comments
    Read more

    Fertilizers formulated for alkaline soils of the Southwest

    Recently I was in an Albuquerque retail nursery where a fertilizer was being sold that stated it was formulated for alkaline soils of the Southwest.  It contained high levels of iron and sulfur, plus the N, P and K major nutrients.  Do any of the readers care to comment on this type of product?    Pros, Cons, etc.  I have my take on it, but I'll entertain what you want to say about it.  Michael Martin Meléndrez
    9 comments
    Read more

    Growing Pecan Trees in Western Alkaline Soil

    It's common to see nutrient and water inhibition compromise the production of pecans in the arid western states, particularly where the soils are high pH, which can tie up nutrients such as zinc, iron, phosphorus and more. Keeping soils moist is also a problem because the regions were we grow pecan are not wet bottomland soils where pecan is native, but are high and dry desert soils where irrigation is essential. If the irrigation water is high in dissolved solids, the problem is made worse. There are many good things Soil Secrets can offer pecan growers that can overcome these obstacles, by improving the moisture management of the soil, improving nutrient solutioning and availability of both the native minerals as well as the purchased minerals, and improving the porosity of the soil so that water and oxygen can penetrate meters deep without the need to subsoil with machinery. How's this done? By using the power of Nature's own bio-chemical called the Carbon Matrix. Starti...
    Post a Comment
    Read more