Details for Cracking the Code: How to Use CEC and Base Saturation Information from Composite Soil Tests

Great question! Your CEC won’t change in your life time. It’s basically a reference of soil texture with single numbers being sandier soil, low teens a loam and anything higher than 20 being silt loam on up to clays. Base saturation is an indicator of cation balance. Watch %Na especially. If your %Mg is too high, your soil is probably hard with little water infiltration. There’s not much you can do with certain ratios but building your Ca:Mg ratio close to 6 is a good goal. Don’t get too caught up with ratios however, stick to sufficiency ranges and soil pH as to how much fertilizer to apply.

CEC not only tell you how many cations it can hold it can also dictate how much soil active herbicide you need to apply to make them work correctly. The combination of organic matter and clay it determines the holding capacity of the soils. You sample indicates a high holding capacity but some low organic sands may only have 4-8 CEC and means nitrogen has to be split applied and even potassium needs to be applied as close to plant use as possible.

Cec is critical because it tells you how much fertilizer you can use, especially your cations base saturation covers a lot Of bases such as proper ratios of things like K & Mag, do we have the right amount of calcium. We recently did a podcast series on the importance of each essential nutrient. If you’d like to check it out let me know if not no big deal 

I’m certain there are more & better scientific explanations from members more educated in this field, but here is my response as ret’d farmer & crop advisor. 1st off yours in in good shape. Low CEC usually indicates sandier soil (loose, larger soil partials) & high, a. higher clay content ( more likely to compact & higher water-holding capacity. The BALANCE in important (see suggested ranges on your test). The closer your Ca, Mg & K are to suggested levels, the better. Low sodium indicates well drained soil. Hi Na or H likely will require some amendment(s) like lime, gypsum or elemental S, etc. I would advise a QUALIFIED soil advisor & more testing before spending $ on an amendment. If soil drainage is inadequate, any amendment other than possibly tiling may be ineffective. I’ve witnessed soils with low Ca and Hi Mg, and usually that interferes with other nutrient availability, usually K deficiency in fruit formation and maturation. A quick look at CEC and BS%’s can be a very good tool to understand if you are considering renting or buying a piece of ground. It could help avoid disappointment.

CEC helps know how much you can hold on the soil but knowing soil texture (sand silt clay %) and OM will tell you this too. The base saturation ratio doesn’t really tell you much unless your CEC is low. However as long as you have enough of the nutrients the ratios don’t matter. If my plate has only 5% meat but it’s the size of a table there more than enough food for me. Lots of veggies and potatoes may go to waste but I’ll have enough meat.

This requires a session. But, think of CEC as chairs in the soil. The Chairs come from OM and clay. Think of Base Saturation as the arrangement of nutrients on those chairs. So too many Mg's might not allow K's to sit in the chairs. Hence why we watch K:Mg ratios.