Thread: CEC formula?
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Old 03-12-2013, 09:43 AM is offline
LawnSite Member
Join Date: Oct 2011
Posts: 16
Amount of organic matter is going to increase your CEC the easiest/cheapest/fastest. CEC is calculated with this formula: K(Potassium) + Mg(Magnesium) + Ca cmol/kg (Calcium centimoles per kilogram) + H (Hydrogen). CEC can also be calculated using Organic Matter and clay, but this is the standard formula.

The formula for determining CEC based on clay is this (this is an example):
If you have a soil that is roughly 20% clay, you can calculate the CEC coming from the clay like this:
0.2 (% clay in soil) x 40 (CEC of clay) = 8cmol/kg soil

Now you must use the same formula to determine how many CECs are coming from the organic matter in your client's soil:

We care going to assume that there is 5% organic matter (just for this example calculation):
0.5 (% humus/organic matter in this soil) x 200 (CEC of humus) =10cmol/kg of soil

8 cmol/kg (clay's CEC in this example) + 10 cmol/kg of soil (CEC from o.m.) = 18 cmol/kg soil

So from this example you can see that the addition of organic matter will increase your client's CEC much faster than anything else, being that o.m. has a much higher CEC than anything else. Hope this helps
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