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The Important Role of Cation Exchange Capacity in Soil

April 29, 2019

The Important Role of Cation Exchange Capacity in Soil

Maintaining healthy soil on your farm, garden, lawn, or landscape is the key to a consistently good crop and plant productivity and quality, but it can often feel like a near-impossible balancing act. You’re trying to keep your soils nourished, fertilized, hydrated, and at a pH of at least five while dealing with elements out of your control like the soil’s natural structure, erratic weather, and other environmental circumstances. Not all soils are created equal, and you may be wasting resources trying to over-nourish your soil when its structure, or chemical makeup, is the real problem. If you need to fix a problem of nutrient leaching, water retention, or low pH, reassessing your soil’s cation exchange capacity is a good way to start.

What Is Soil Ion Exchange Capacity?

Soil exchange capacity refers to the total capacity of soil to hold exchangeable ions and it influences the soil’s ability to hold onto essential nutrients and provide a buffer against soil acidification.

Cation exchange capacity (CEC) is a soil’s total capacity for exchangeable cations, which are positively charged ions. The main ions associated with CEC are calcium (Ca2+), magnesium (Mg2+), sodium (Na+), and potassium (K+). These cations are heavily basic, so if the soil becomes increasingly acidic, they will be replaced by other ions.

Your soil’s CEC is essentially determined by clay mineral and organic matter components of soil, which both possess negatively charged sites on their surfaces to absorb positively charged ions through electrostatic force. Many cations function as essential nutrients for many plants, so soil with lots of clay and organic matter that can absorb large amounts of positive ions is typically more fertile.

Anion exchange capacity (AEC) is the capacity of a soil to adsorb or release anions under normal soil conditions. Anions are negatively charged ions. Within the soil, they increase with low pH and decrease with high salt concentration. It’s not as heavily studied or emphasized as cation exchange, but it does impact your soil’s ability to remain properly nourished.

What Impact Does Soil Ion Exchange Capacity Have On Plant Quality and Productivity?

Plant Quality Impacted By Soil Ion Exchange CapacityCEC heavily influences important features like soil structure stability, nutrient availability, soil pH and the soil’s reaction to fertilizers and other ameliorants. Having low CEC can accelerate the deterioration of your soil’s pH, as it becomes more vulnerable to things like nitrogen fertilizer and nitrate leaching.

Soils with low CEC will very often suffer from a deficiency in important nutrients like potassium and magnesium, which slip through the cracks of the soil rather than attaching to negatively charged sites. Soils with higher levels largely resist this harmful leaching, thus allowing them to retain essential nutrients and maintain a higher water-holding capacity.

Soil doesn’t retain anions like nitrate or sulfate at significant levels, which leaves phosphate as the primary anion of importance within your soil. Anion exchange is important in the process of releasing fixed phosphate within the soil to make it available to plants. This process occurs within the replacement of the clay minerals; OH ions.

How Can Farmers Manage Their Soil Cationic Exchange Capacity?

Because the CEC is so reliant on your soil’s natural structure and composition, and because of the complexity of the biological system found in soils, it can be difficult to dramatically alter ion exchange capacity in soil. Pure sand, for instance, has a relatively low CEC, while clay structures generally have higher levels. If you have less than optimal CEC levels, you can still improve your crop yields and plant productivity and quality.

The most obvious solution to soils with low CEC is to raise the organic matter in their composition. Organic matter will increase your soils CEC levels, nutrient and water retention, and resistance to fluctuating or declining pH levels.

You can estimate your soil’s CEC by assessing its texture and color, but for a more comprehensive understanding, you’ll need to send it along to a laboratory. Labs test the soil using one of two methods—direct or summation. The direct method requires the mixture of cations on the exchange sites to be replaced with a single cation such as ammonium (NH4+). That exchangeable NH4+ is replaced with another cation and then the amount of NH4+ exchanged is measured.

The summation method is more common, done by summing the calcium, magnesium, and potassium in soil test and estimating the exchangeable hydrogen obtained from the buffer pH. These CEC numbers will usually be lower than those obtained through the direct method.

How Does Cool Terra Help Soil Ion Exchange Capacity?

Cool Terra For Soil Ion Exchange CapacityCool Terra® Organic is a biochar-based, fixed carbon, material that optimizes key soil performance characteristics for greater productivity and sustainability. Cool Terra is specifically engineered to strict criteria to ensure that it works consistently and predictably when easily applied to the soil root zone. Through a patented production process, Cool Terra is engineered to be neutral pH, hydrophilic (which means water-loving) instead of hydrophobic (which means water repelling) as most raw biochars are, and contain high ionic exchange capacity.

Cool Terra’s high ion exchange capacity (both CEC and AEC) can promote nutrient exchange and availability, holding nutrients in the root zone longer. For soils with limited cation and anion exchange capacities, the addition of Cool Terra can help to optimize the soil and promote plant growth and quality.

Improve Soil Quality with Cool Terra®

If you’re here doing the research as to how to improve your soil’s ion capacity, you’re already taking a step in the right direction. Soil is the foundation for consistently high-quality crop yields, and monitoring its CEC is integral to keeping yours healthy. Adding organic matter to your soils like Cool Terra is a great step towards soil health, and it’s one of the keys to making sure your land is able to resist external threats that might negatively impact the ion exchange capacity and pH levels of your soil. On top of that, Cool Terra builds soils structure, optimizes water and nutrient efficiencies, provides a beneficial habitat for soil microbes, all the while sequestering carbon. Revitalize your soil, grow with Cool Terra, and support a healthier environment.


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