In the efforts to improve our soils often we focus exclusively on adding nutrients to improve vegetation performance, when really there is another soil process that must come into consideration as well. This process has the intimidating name of the soil’s cation exchange capacity- but is actually quite an easy concept to understand. And by understanding this process at work in all soils we can improve our vegetation efforts and reduce costs on our site.
For nutrients to be taken up by plants they must be dissolved. Nutrients that are dissolved are referred to as cations and anions. Cations are the positively charged particles(1) and include most nutrients vital to plant success. So, in layman’s terms the Cation Exchange Capacity (CEC) of soils is its ability to retain those vital nutrients and ensure they are available and in a form the plant can utilize.
What does that mean? Consider a parking lot analogy. The nutrient cations, “cars”, need somewhere to go if they are going to be able to park and stay in the soil. The higher the Cation Exchange Capacity in your soil the more “parking spaces” are available to hold those nutrients. The more parking spaces, the more cars… thus the higher your soil’s nutrient holding capacity- which means the more nutrients available for plants to utilize. The easy takeaway is this: If you are adding soil nutrients through soil amendments, but NOT also focused on raising your CEC levels then you are basically throwing your money away as the nutrients will simply leach out of your soils and will not proving the benefit you intended for your soils.
Another problem that may be encountered is if you also added organic matter as well as nutrients, but are still not seeing an increase in Cation Exchange Capacity and nutrient holding capabilities in your soil then the issue may be an organic material that is not being broken down correctly. This can be the result if you add organic matter without paying attention to cation exchange and added too much high carbon material all at once (for example, wood chips.)
Good cation exchange levels are generally considered to be ideal if they reach or exceed 20 meq/100 g. Peat moss provides a Cation Exchange Capacity ranged from 108 to 162 meq/100 g. (2), making it an ideal addition for both soil tithe improvement as well as dramatically improving a soil’s Cation Exchange Capacity. This makes it an excellent soil amendment and explains it’s long and successful usage by multiple industries that have growing plants as part of their business model. Humus and compost also have high cation exchange levels, but are short lived in soils and need replacement often, unlike sphagnum peat moss, which is very long lasting.
Cation Exchange Capacity should be something we consider hand in hand with adding nutrients to our soils to promote better and longer lasting vegetation success. The ability for soils to absorb more nutrients and hold onto them longer ensures lower maintenance requirements and costs through the reduction in the number and frequency of fertilizer applications.
- Soil-Nutrient Relationships.. Soil Nutrion Management Program for Maui County. University of Hawai’I at Manoa. September, 2015.
- Cation Exchange Capacity and Base Saturation Variation among Alberta, Canada, Moss Peats. Janet F.M. Rippy and Paul V. Nelson. Department of Horticultural Science, Box 7609, North Carolina State University, Raleigh, NC 27695