## What is an exchangeable cation?

Exchangeable cations refer to the positively charged ions which are loosely attached to the edge of clay particles or organic matter in the soil. The cations include Calcium, Magnesium, Potassium, Sodium, Hydrogen and Aluminium.

### What is exchangeable cation exchange capacity?

Cation exchange capacity (CEC) is the total capacity of a soil to hold exchangeable cations. It influences the soil’s ability to hold onto essential nutrients and provides a buffer against soil acidification. Soils with a higher clay fraction tend to have a higher CEC. Organic matter has a very high CEC.

How is the cation exchange capacity of soil determined?

To determine the cation exchange capacity (CEC), calculate the milliequivalents of H, K, Mg, and Ca per 100g of soil (meq/100g soil) by using the following formulas: H, meq/100g soil = 8 (8.00 – buffer pH) K, meq/100g soil = lbs/acre extracted K ÷ 782. Mg, meq/100g soil = lbs/acre extracted Mg ÷ 240.

What are the major exchangeable cations in soils?

The five most abundant exchangeable cations in the soil are calcium (Ca++ ), magnesium (Mg++), potassium (K+), sodium (Na+) and aluminium (Al+++). Cations are held by negatively charged particles of clay and humus called colloids.

## Why Does clay have a high CEC?

CEC is an inherent soil characteristic and is difficult to alter significantly. It influences the soil’s ability to hold onto essential nutrients and provides a buffer against soil acidification. Soils with a higher clay fraction tend to have a higher CEC. Organic matter has a very high CEC.

### What is a good CEC for soil?

Typical CEC Values in Soils

Table 1. Cation exchange capacities at pH 7.0 of different soil types, textures and soil organic matter.
Fine Sandy Loam 5-10
Loam 5-15
Clay Loam 15-30
Clay >30

What are the basic cations?

Ammonium, calcium, magnesium, potassium, and sodium are known as the ‘base cations,’ while aluminum and hydrogen are known ‘acid cations. ‘ * Unlike the other base cations, sodium is not an essential element for all plants.

What’s an example of a cation?

Cations are positively charged ions. They are formed when a metal loses its electrons. Therefore, they possess a net positive charge. Some examples of cations are Calcium (Ca2+), Potassium (K+), hydrogen (H+).

## Which clay mineral has highest CEC?

Soil type and CEC Pure sand has a very low CEC, less than 2 meq/100 g. Clays such as kaolinite have a CEC of about 10 meq/100 g, while illite and smectite have CECs ranging from 25 to 100 meq/100 g. Organic matter has a very high CEC, ranging from 250 to 400 meq/100 g.

### What does the CEC mean in soil sample?

Cation exchange capacity
Cation exchange capacity (CEC) is a measure of the total negative charges within the soil that adsorb plant nutrient cations such as calcium (Ca2+), magnesium (Mg2+) and potassium (K+). As such, the CEC is a property of a soil that describes its capacity to supply nutrient cations to the soil solution for plant uptake.

Is a high CEC good or bad for plants?

Cations on the soil’s exchange sites serve as a source of resupply for those in soil water which were removed by plant roots or lost through leaching. The higher the CEC, the more cations which can be supplied. This is called the soil’s buffer capacity.

What are some examples of cations?

They are formed when a metal loses its electrons. They lose one or more than one electron and do not lose any protons. Therefore, they possess a net positive charge. Some examples of cations are Calcium (Ca2+), Potassium (K+), hydrogen (H+).

## How to calculate base cation exchange capacity in soil?

Table 2. The meq/100g soil constants for the base cations Ca, Mg, K, and Na. Base Cation Atomic Weight Charge (Valence) Gram Equivalent Weight (g) Milliequivalent/ 100 g soil Calcium (Ca) 40 2 20 200 Magnesium (Mg) 24 2 12 120 Potassium (K) 39 1 39 390

### How are CEC and exchangeable bases determined in calcareous soils?

The determination of CEC and exchangeable bases in calcareous soils has always been very difficult, because partial dissolution of the phases (e.g. CaCO3) is observed in these matrices as a result of interaction with the exchange solution rich in electrolytes.

What is the detection limit for cation exchange?

The method has detection limits of approximately of 1 ppm or 0.01 meq/100g for each cation. The estimation of cation exchange capacity is reported as the sum of the results for K, Ca, Mg, and Na.

How to calculate the exchangeable acidity of soil?

Calculate exchangeable acidity, using the buffer pH with the empirically derived conversion equation (Table 3). If the soil has a pH greater than 7.0, you essentially have no exchangeable acidity and CEC is just the sum of base cations.