What is Cation Exchange Capacity (CEC)?

What is CEC?

Cation Exchange Capacity (CEC) is a vital property of soil or rootzones, measured to develop suitable nutritional programmes.

This measurement informs the selection and frequency of product applications, ensuring optimal plant health.

Essentially, CEC can be described as the soil or rootzone’s ability to hold onto positively charged ions, known as cations.

By holding these cations, the soil prevents their rapid movement out of the rootzone, making them available for plant uptake.

Key Cations in Soil

The primary cations relevant to soil health and plant nutrition include potassium, calcium, magnesium, and ammonium.

Other cations that may be present, include sodium (particularly in saline conditions), iron, aluminium, and hydrogen. The balance of these cations in the soil significantly influences the overall nutrient availability to plants.

Understanding CEC Values

CEC values are influenced by the amount of reactive surfaces in the soil, primarily clay and certain types of organic matter, which carry an overall negative charge. In sports turf settings, sand is commonly used for its drainage properties but has a very low CEC.

Pure sand can have CEC values as low as 2 to 5. Adding organic matter or clay can increase CEC values to around 10, and typical soils can range into the 20s or mid-20s. Pure clay or high organic matter content can result in even higher CEC values, though these are rare in isolation.

Improving CEC

CEC can be influenced both during construction and through ongoing maintenance. During construction, sand is often amended with materials like peat, sandy soil, or stabilised compost to increase CEC.

These amendments add reactive surfaces that enhance the soil’s ability to hold and release nutrients.

In maintenance or renovation, top dressing with organic matter or inorganic amendments, such as zeolite (a mined mineral with high CEC), can also improve soil CEC. However, these methods require careful mixing to ensure uniform distribution and can add costs to the process.

Nutritional Strategy Based on CEC

Understanding CEC is crucial for developing an effective nutritional strategy. Soils with low CEC are not as effective at retaining nutrient cations, requiring more frequent application of nutrients to prevent plant deficiencies.

Liquid nutrition and regular spoon feeding are common practices during the summer, along with selecting slow-release or controlled-release nutrients to ensure continuous availability for plant uptake.

Debunking CEC Myths

There are claims in the industry that fertilisers can influence soil CEC.

However, in practical terms, the application of fertilisers at typical rates (e.g., 30-50g/m2) is unlikely to significantly change the CEC of the bulk rootzone, which weighs around 100kg/m2 of turf.

Any theoretical increase in CEC from fertilisers would be negligible.

These misconceptions often arise from the confusion between the effects of organic amendments used in construction or renovation (applied at much higher volumes) and regular fertiliser applications.

Conclusion

Understanding and managing CEC is essential for effective soil and plant health management.

By considering CEC values, adjustments can be made to both construction and maintenance practices to optimise nutrient availability.

While CEC is not the only factor in developing a nutritional programme, it plays a significant role in ensuring the effective delivery of nutrients to plants.