Adsorb means to attract and hold molecules, ions, or particles on the surface of a material rather than absorbing them into its interior. In soils, negatively charged clay minerals and organic matter adsorb positively charged nutrient ions such as potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), and ammonium (NH₄⁺), helping prevent them from being washed away by water.
Adsorption is a key process behind cation exchange capacity (CEC), which determines how well a soil or growing medium can retain and release nutrients for plant roots. Materials with a high surface area and many charged sites, such as clay and organic matter, generally have a greater ability to adsorb nutrients.
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