Understanding Soil Cation Exchange Capacity (CEC) and How to Improve It
Cation Exchange Capacity (CEC) is a fundamental concept in soil science that plays a crucial role in determining soil fertility and its ability to support plant growth. Whether you are managing sports turf, agricultural fields, or garden soil, understanding CEC can help you make informed decisions about soil management practices. In this post, we'll explain what CEC is, why it matters, and how you can improve it to enhance soil health and productivity.
What is Cation Exchange Capacity (CEC)?
CEC describes the total number, or the soil’s ability to hold and exchange positively charged ions, known as cations - examples include calcium (Ca²⁺), magnesium (Mg²⁺), potassium (K⁺), and ammonium (NH₄⁺). You’ll recognise these elements throughout the turf industry as Trace Elements (TE). The higher the CEC, the higher the negative charge of the soil, and therefore greater numbers of cations can be held. CEC is measured in millequivalents per 100 grams of soil (meq/100g) which can be numerically proportionate to cmolc/kg, another metric used.
Soils with a high CEC are therefore more fertile because they can hold onto more nutrients. Conversely, soils with low CEC may struggle to retain nutrients, leading to potential deficiencies and requiring more frequent fertilization.
In the early days of sports turf, fertiliser inputs were characterised by the three basic inputs – Nitrogen, Phosphorus and Potassium. Today we have developed a deeper understanding of what exactly is needed to produce immaculate playing surfaces all year round and sports turf managers have to take a holistic approach to not only the grass plant, but the health of the underlying soil as well.
On a ‘push up’ golf green, or one constructed of ‘natural’ soil, the annual Nitrogen input could be in the region of 8kg – 14kg /Ha per year and Trace Elements need only be applied occasionally. On a green constructed to USGA specifications, a normal range could be between 25kg – 30kg Nitrogen per year, and with the understanding of CEC and nutrient leaching above we know that USGA spec constructions need Trace Elements to be applied more frequently as well
Factors Influencing CEC
CEC is primarily determined by the composition of the soil. Sand has a very low CEC, again, capacity to hold on to nutrients, whereas a clay and organic matter have a much higher CEC. Adjusting the balance of soil composition is not easy after construction, especially in a soil with a high sand content. Generally, the addition of the Trace Elements and/or applications of humic acid can raise the CEC in the short term. Increasing the organic matter or clay content within the soil is the most sustainable way to keep CEC high long term. Optimum organic matter levels within the soil will not only increase it’s CEC but enhance the soil structure, increase moisture retention, and boost microbial activity too. The addition of clay amendments such as bentonite or zeolite will also boost the CEC of the soil.
Soil pH also plays a role in a soil’s, but perhaps more specifically the clay or organic matter’s ability to provide nutrients to turf. Optimal soil pH should be between 6-7 and can be adjusted up with applications of Calcium Carbonate, or down with sulphur (beware black-layer!) or organic matte..
Cation Exchange Capacity (CEC) is a key indicator of soil health, reflecting the soil's ability to retain and supply essential nutrients to plants. By understanding and managing CEC, you can create a more productive and sustainable growing environment. Improving CEC through organic matter additions, pH adjustments, and appropriate soil amendments can lead to better soil structure, increased nutrient availability, and healthier plants.