What is Soil Cation Exchange Capacity?
Soil cation exchange capacity (CEC) is a measure of the soil’s ability to store or hold groups of nutrients, specifically, elements that have a positively charged ion, more commonly known as cations. Soil CEC is a critical soil property which impacts buffering capacity, nutrient availability and reactions to applied nutrients like nitrogen fertilizers.
While soil CEC is a critical component for soil and nutrient management, there are common misconceptions when it comes to its relationship with nutrients. To understand the relationship between soil CEC and nutrients, we first need to understand the chemistry behind the soil and the nutrients found or applied to the soil.
Common cations found in the soil include calcium, magnesium, potassium, ammonium, hydrogen and sodium.
Soils with high CECs are generally soils with high clay and organic matter content. Clay surfaces are negatively charged meaning the cations in the soil are adsorbed to these negatively charged particles. While cations are attracted to clay or organic matter, they are not permanently bound, so plant roots can exchange cations, like hydrogen, for the nutrient cations that are needed for plant growth and development, like ammonium. This exchange of nutrients is charge-based. For example, for one Mg2+ it would require 2H+ for the exchange to occur.
What about the nutrients that are negatively charged ions (anions), such as nitrate? Since a negative does not attract a negative, anions are not held by the soil CEC, making nitrate more susceptible to leaching.
Common Soil CEC Myths
Some growers view soil CEC as a measure of nitrogen holding capacity and many believe that soils with lower CECs do not have the ability to hold higher rates of nitrogen. As a result, some advisors and growers may be basing their nitrogen rates on soil CEC, following the old rule of thumb of 10 lbs of nitrogen per unit of CEC per application and opting to lean more heavily on practices like split-applied nitrogen, which can lend to operational inefficiencies, higher costs, and a different suite of risks.
The truth of the matter is soils with low CEC can hold more nutrients than one may think. According to the University of Illinois, one unit of CEC in the topsoil can hold up to 360 lbs of ammonium1. To limit nitrogen application rates based on soil CEC can potentially limit the nutrients a crop may need or expose the grower to risks that later-applied nitrogen is never taken up by the plant.
In addition, soil CEC has no bearing on anions or negatively charged ions, such as nitrates which is another form nitrogen plants can uptake. So, regardless of soil CEC, nitrate is still susceptible to loss via leaching and denitrification.
We encourage growers to work with state and local extension services or advisors to best determine application rates for nitrogen and other nutrients.
Protecting Nitrogen – No Matter the CEC
So how do nitrogen stabilizers fit in? We’re glad you asked.
Nitrogen stabilizers, such as ANVOL® and CENTURO®, can help protect nitrogen applications from above- and below-ground loss, respectively. These solutions provide growers peace of mind when it comes to maximizing a fertilizer investment. By protecting the nitrogen applied, growers may be able to reduce the number of applications, improving efficiency, reducing cost, and mitigating uptake risks – even with low soil CEC.
As mentioned earlier, no matter the soil CEC, nitrate does not adhere to the soil and is susceptible to losses via leaching and denitrification. CENTURO is a proven nitrification inhibitor for anhydrous ammonia and UAN that slows the nitrification process - the conversion of ammonia, a more stable form of nitrogen, to nitrate – capitalizing on the substantial capacity of the CEC to hold ammonium and allowing more time for crop uptake. By keeping nitrogen in the ammonium form longer than without an inhibitor2, growers can get the most out of their fertilizer investment.
ANVOL offers the longest-lasting protection against ammonia volatilization over a wider range of soil environments. ANVOL features dual active ingredients - NBPT which slows down the hydrolysis of urea as soon as it’s applied, then Duromide, Koch’s patented molecule, which extends the protect even longer. And with a lower treatment rate for more efficient coating and a drier finish to urea, ANVOL can help reduce labor demands.
To learn more about soil CEC, the relationship with nitrogen management or nitrogen stabilizer solutions, reach out to your KAS representative today.
1 Nafziger, E. "Soil Nitrogen and N Management Following the 2016 Crop." Department of Crop Sciences, University of Illinois at Urbana-Champaign, November 14, 2016.
2The underlying data is based on third-party laboratory studies funded by Koch Agronomic Services; results may vary based on a number of factors, including environmental conditions.
CENTURO is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Results may vary based on a number of factors, including environmental conditions. Improvements in nutrient use efficiency, yield and nitrate leaching may not be observed in all cases.