# Low CEC with clay soil



## CLT49er (Jun 19, 2020)

I dont know much about CEC. From what Ive google is that a low CEC number in your soil test typically means you have sandy soil that doesnt hold nutrients well. I have purely clay soil and my soil test says 5. Doesnt that contradict each other? What does this mean?

I am outside Charlotte NC and have a new build house. Contractor plowed away all organics and layed bermuda sod on it. Soil test came back with low P and high K. So I started the year off a high P starter fertilizer. And I laid lime. Since then Ive been using Cx diy, Next RGS, Microgreen, and Green Pop (high P).


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## Ridgerunner (May 16, 2017)

CEC (Cation Exchange Capacity is a measurement of a soil's ability to hold Cations (e.g. positively charged elements Potassium, Calcium, Magnesium, Sodium, Hydrogen, etc) to certain soil particles/substances. More specifically, It is the result of the electro-magnetic (like a magnet) characteristics of negatively charged clay and humic substances in the soil that adsorb Cations. So CEC is a reflection of the amount of clay and humic substances in a soil. Humic substances have a very high capacity to hold Cations (100-500+ meq per 100 grams), but most soils don't have a high percentage of humic content, nor would that be desirable. Normally, clay has a lesser, but still substantial capacity (25-50 meq per 100 g). So a soil with no Humic substance and no clay content would have a 0 CEC. Some clays however are so weathered by time that they have lost much of their CE capacity (mostly through an absorption process where their actual physical structure has changed resulting in less negative charge). This is most common in the U.S. Southeast, particularly in what is known as the "Piedmont Region. Soil in that region typically has low Humic content and high weathered clay content, so their CECs can be quite low. Consequently a CEC of 5 is common.


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## Gilley11 (Nov 3, 2019)

@Ridgerunner is there an optimal CEC range to be in?


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## Ridgerunner (May 16, 2017)

Gilley11 said:


> @Ridgerunner is there an optimal CEC range to be in?


That's a near impossible question to answer. IMO it depends. As Roseanne Roseannadanna would say: "It's always something."
For instance:
On the low threshold end of CEC, to meet the minimum requirements of nutrient availability levels per MSLN guidelines, you'd need a CEC of about. 3.5, but the ratios of the major Cations and hydrogen would need to be spot on-not likely to be achieved. Therefor, you'd want a fudge factor of at least another 2 meq of CEC to have a chance of reaching the minimum nutrient values for each of the major Cations.
On the high end, you'd think the higher the CEC, the better, as the soil would hold massive amounts of nutrients, but increased CEC would mean higher OM/humic substances or higher clay content. High OM can result in higher soil moisture retention which can increase incidence of disease and promote root rot etc. Higher clay content can impede rooting. (This is the likely reason recommended sufficiency levels are higher for clay soils than for sandy soils.)
So, ideally you'd want a soil with a texture ("loam") that doesn't impede rooting, allows for good drainage (prevent water logging) while still retaining enough moisture to supply the turf for an extended period of time between irrigation applications, and enough OM and clay content to produce sufficient CEC to hold the amount of nutrient needed to supply the turf with it's needs between fertilizer applications without producing poor turf performance (subjective) and without adversely affecting the soil characteristics of drainage, moisture content or rooting. 
It's been my observation that any CEC greater than 7-8 produces "banking" sufficient to result in good performing turf with standard fertilizing practices. Less than 6-7 will usually require some form of spoon feeding to make up for the lack of soil "banking."


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