cation exchange capacity by walts organic fertilizersThis is a complicated subject, and we don’t claim to be experts, but here is a quick and dirty explanation.

A soil’s ability to react with positively charged molecules is called it’s cation exchange capacity (CEC). The higher the CEC, the higher the negative charge of the soil and the more cations that can be held. The most common soil cations are: calcium, magnesium, potassium, ammonium, hydrogen and sodium.

Generally soils with more clay silt and organic matter have a higher CEC and the CEC decreases with increased sand content.

The most basic thing to remember is CEC indicates how well your soil will hold onto anything, including nutrients and water.

Below are some practical implications of your soil’s Cation Exchange Capacity:

 

 

  • Low CEC soils need quick but frequent waterings, while high CEC soils need slow water applyed less often.
  • When applying fertilizers and soil conditioners to low CEC soil, it is best to apply a little at a time to avoid the risk of leaching them through the soil and into ground water.
  • When applying nutrients to high CEC soils it is best to incorporate them, if they are placed on the surface they are more prone to run-off due to the slow infiltration rate.
  • The lower the CEC of a soil, the faster the soil pH will decrease with time.
  • Soils with a low CEC are more likely to develop deficiencies in calcium, potassium & magnesium.
  • Because they are resistant to leaching, high-CEC soils generally do not need to be limed as frequently as low-CEC soils; but when they do become acid and require liming, higher lime rates are needed to reach optimum pH.

How do I increase my CEC?

Depending on the scale of your growing operation this can be a difficult task.

For smaller areas compost, worm castings and biochar are a great ways to add organic matter and increase your CEC.

If you are dealing with large fields realistically your best approach would be to adjust your management to account for the low CEC according to the implications outlined above.\

 

 

Sources:

https://www.extension.purdue.edu/extmedia/ay/ay-238.html

http://nmsp.cals.cornell.edu/publications/factsheets/factsheet22.pdf

http://msue.anr.msu.edu/news/what_is_your_soil_cation_exchange_capacity