Nitrate Adsorption Model for Georgia Variable Charge Subsoils
Qafoku, Nikolla P.
Sumner, Malcolm E.
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Nitrate adsorption in subsoil affects nitrate leaching, which in tum can affect water quality. A model to describe the adsorption of nitrate in acidic variable charge subsoils in Georgia and other tropical and subtropical areas is proposed. In the first step, a portion of the effective charge that vanishes as a result of the overlapping of oppositely charged diffuse layers on different colloids, termed "the mutually neutralized charge", σ[subscript M]. is established. The "newly developed charge", σ [subscript N], is developed during the second step, in response to ionic strength increase in subsoil solution. The reestablishment of these two components of the effective charge causes "salt adsorption". The last step is "ionic exchange" with the corresponding effective charge component σ EX. The separation of ''temporarily effective" (σ[subscript M] + σ [subscript N]) from "permanently effective" (σ [subscript EX) portions of the effective charge is very crucial when displacement and transport of ions like N₃- are considered, in order to understand that these ions are only temporarily adsorbed and can be immediately leached out by rain.