Calculating Cation Change Potential, Ft Saturation, and Calcium Saturation

Calculating Cation Change Potential, Ft Saturation, and Calcium Saturation

The goal of this particular fact layer should be to explain floor cation replace strength, feet saturation and you may calcium saturation, and you will demonstrated just how this type of beliefs is calculated into the floor test account.

Cation Change Capability (CEC)

Cation exchange ability (CEC) are a simple ground possessions familiar with anticipate plant nutrient availability and maintenance on soil. This is the potential away from available nutrient have, maybe not a direct dimension of offered nutrients. Soil CEC typically expands given that clay blogs and organic count increase because the cation exchange happen towards counters away from clay vitamins, natural number, and root. Earth in Kansas normally involve a broad CEC diversity, but normally fall approximately 5 so you’re able to 25 meq/a hundred grams soil (Dining table 1). Values over twenty five meq/100 grams floor are located which have heavier clay earth, natural, or muck soils.

Cation exchange capacity is defined as a soil’s total quantity of negative surface charges. It is measured commonly in commercial soil testing labs by summing cations (positively charged ions that are attracted to the negative surface charges in soil). Exchangeable cations include base cations, calcium (Ca 2+ ), magnesium (Mg 2+ ), potassium (K + ) and sodium (Na + ), as well as acid cations such as hydrogen (H + ), aluminum (Al 3+ ) and ammonium (NH4 + ).

(Ca 2+ + Mg 2+ + K + + Na + ) + (H + + Al 3+ + NH4 + )

Figure 1 illustrates a reduced CEC surface, that have a small number of bad charge and you can related cations (left) and you may a premier CEC surface which have a much bigger amount of negative charges, occupied because of the a lot more overall cations (right).

Legs Saturation

Foot saturation is determined due to the fact part of CEC filled because of the base cations. Figure 2 suggests one or two earth with the same CEC, although surface to the right keeps a lot more legs cations (inside blue). Therefore, this has a high feet saturation. Ft saturation try directly about pH; since legs saturation develops, pH develops.

Similarly, we are able to determine the base saturation each personal foot cation. Calcium supplements feet saturation are determined due to the fact portion of CEC occupied of the calcium supplements cations. In the Profile dos, the latest soil off to the right keeps doubly of several calcium cations (California 2+ ), ergo a top calcium saturation.

Figuring CEC from a dirt Decide to try

CEC is actually claimed just like the milliequivalents each one hundred g of ground (meq/100g), otherwise costs per pounds out of soil. Milliequivalents can be used in the place of pounds due to the fact charge is far more of good use whenever these are ion change.

Very, how do we grab the concentration of diet inside a dirt test (ppm) and you can become charges (meq/100g floor)? Ground assessment labs usually give these beliefs already on crushed test declaration, or deliver him or her through to request. But not, attain a far greater understanding of the new relationship, the newest procedures to do this type of calculations is in depth below.

Step one: Influence brand new gram equivalent lbs of each and every base cation. Each foot cation possess an atomic pounds and you can valence matter (charge) regarding the unexpected desk out of issues. Shape 3 shows the base cations. Having calcium, brand new atomic pounds try

40 grams for every mole while the costs was dos. I split per nuclear lbs (40) because of the fees (2) in order to determine brand new gram comparable lbs (20). The benefits for every single ft cation is intricate inside the Table 2.

3. Proliferate the latest gram equivalent weight from the ten to convert so you’re able to meq/100g from soil. Once more, having calcium supplements, new gram comparable weight out of 20 g increased from the ten gives us 2 hundred meq/one hundred g surface. That it meq/100g surface well worth is utilized while the a sales grounds towards the nutrient amount viewpoints (ppm) obtained when you look at the a dirt take to. The fresh bolded philosophy in the last line when you look at the Dining table dos can be be studied just like the a conversion process foundation when and does not alter.

Step 4. Transfer crushed shot mineral concentration in order to fees. Dining table 3 brings a typical example of regular floor attempt account in Ohio (during the ppm). We could determine the fresh new cumulative costs each cation uses up for the replace web sites by using the costs calculated when you look at the Table 2 (history column) and you can dividing them by soil sample account. To own calcium, a soil decide to try level of 2000 ppm, split up of the two hundred translates to ten.0 meq/a hundred grams surface. This is accomplished each cation myself.

Action 5. Determine collective fees away from feet cations. Next, i make sense the newest fees of each and every base cation. For this analogy, the sum of legs cations translates to several.4 meq/100g crushed (Desk step three).

Action six. Estimate exchangeable acidity, using the shield pH with the empirically derived conversion equation (Table step three). In the event the floor has a beneficial pH more than eight.0, you basically have no exchangeable acidity and you may CEC is just the amount of foot cations. A soil which have a shield pH of six.6 implies that acidic cations consume 4.8 meq each a hundred grams out-of ground.


Cation change capability and you can legs saturation are very important floor specifications you to help determine how a soil is actually addressed and you can fertilized. Whenever you are standard floor analysis laboratories commonly assess and you can statement this type of viewpoints inside surface attempt accounts, it’s beneficial to has actually a solid comprehension of CEC and you will base saturation calculations.


Reganold and you may Severe. (1985). Declaring cation change capability within the milliequivalents for every single a hundred g and also in Si equipment. Record of Agronomic Education 14(2): 84–90.

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