How does cation exchange capacity (CEC) impact my lawn/garden?

What do chemistry and lawn care have in common? A lot actually. If you recall the term cation from any previous chemistry class, then you may already be familiar with cation exchange capacity (CEC for short). In case you need a refresh, a cation is an element/molecule that has a positive charge. In terms of lawn care, you want to make sure your lawn has enough cation nutrients like calcium, magnesium, and potassium and a lower percentage of things like sodium and aluminum. This is why it is important to understand cation exchange capacity and how exactly it affects your lawn.

What is cation exchange capacity? Well, according to Mr. Buck Farrior, agronomist at Agritech, CEC is defined as “the measurement of positive charge per kilogram of soil.” Mr. Farrior continued, “clay particles and organic matter are negatively charged. The cations are positively charged. This holds the cations in place and makes it possible for the plant roots to take a solution of water and cations into the plant.” This is why soils with large amounts of organic matter tend to have a higher CEC.

How to Test

How exactly is it measured? Before deciding whether or not to get a lab test involved, it is relatively easy to pinpoint less favorable CEC. Texture is a huge factor. It is important to understand the amount of sand, silt, and clay present in your soil to determine its CEC. Mr. Farrior suggests, “you can often tell by the texture. If you roll [the soil] in your fingers and it crumbles down or falls away, that indicates a gritty sandy soil.” These sandy soils tend to have a lower CEC of around 3-5 cmol(+)/kg. Mr. Farrior explains that this is not necessarily harmful, per se, it just requires more maintenance. If your soil is gritty like this, it will just require you to mediate your fertilizer, meaning, don’t fertilize all at once.

Mr. Farrior offers a solution. “You can manage low CEC sand soils with the addition of water and nutrients.” Doing things like adding organic matter will improve a low CEC. If you send your sample to a lab, they will check for conductivity and for the amount of cations present, but generally they will suggest similar solutions, making it fairly easy to tackle the problem yourself.

Testing Soil Composition by Hand

CEC Scale

The cation exchange capacity scale runs anywhere from 3 to 50 cmol(+)/kg or meq/100g (centimoles positive charge per kilogram of soil OR milliequivalents positive charge per 100 grams of soil, which are equivalent units). As Mr. Farrior explains, “If you are in the midwest or northwest with glacier soils, the CEC is 20-25.” Usually, the lower the CEC, the harder your lawn is to manage. Sandier and highly weathered soils tend to be at the lower end of the range, 3-5. Soils that are heavy in organic matter typically tend to be in the higher ranges. Maintaining an optimal soil pH (usually around a 6) and adding organic matter would help to manage and/or raise a low CEC. Also, Mr. Farrior explains, “if you reduce the amount of tillers that you do that would help. They are useful to manage weeds but are destructive to soil structure and quality.” According to Mr. Farrior, some of the desirable percentages of nutrient cations found in the CEC are about 60-80% calcium and 10-15% magnesium. 

To conclude, cation exchange capacity is an important aspect of any soil, and you can increase it by adding organic matter. As it turns out, chemistry and lawn care have a lot more in common than you would think!