CEC, or Cation Exchange Capacity, is a measure of how well soil can retain and supply cations to plant roots. It is an important indicator of soil fertility and is determined through various methods, with the most common approaches being:
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Soil Sampling: Collect a representative soil sample from the area of interest. Typically, samples are taken from the topsoil (0-15 cm depth).
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Sample Preparation: Air-dry the samples and remove large debris. It may also require grinding to obtain a uniform particle size.
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Cation Exchange Procedure: The soil is saturated with a solution of a known cation, usually ammonium (NH4+) or sodium (Na+). This is done by adding a solution of ammonium acetate, which replaces the cations attached to the soil particles.
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Wash and Displace: After saturation, the soil is leached with distilled water to wash away excess cation solution, ensuring that only the cations held by the soil are retained.
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Extraction of Cations: The retained cations are then extracted using a specific leaching solution.
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Analysis: The extracted solution is analyzed using methods like atomic absorption spectrophotometry (AAS) or inductively coupled plasma (ICP) to determine the concentration of the cations (e.g., calcium, magnesium, potassium, sodium).
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Calculation of CEC: The total cation concentration is calculated and expressed in milliequivalents per 100 grams of soil (meq/100g), which represents the CEC of the soil.
This laboratory method helps assess the soil's nutrient-holding capacity and its ability to supply essential cations to plants, thereby informing soil management practices.