Potassium and Ammonium Fixation by Vermiculitic Soils

Abstract

Abstract The fixation of potassium (K) and ammonium (NH 4 ) against removal by unbuffered salts under wet and air‐ and oven‐dry (110C) conditions by vermiculitic soils is reported. Under wet conditions, the soils exhibited a rather definite capacity to fix NH 4 and K; amounts of NH 4 and K fixed were essentially equal. Exchange capacity reductions accompanying wet fixation demonstrated that an irreversible exchange adsorption mechanism would account for practically all of the NH 4 and K fixed. The amount of NH 4 and K fixed under air‐ or oven‐dry conditions was comparable to the amount fixed under wet conditions where the amount of NH 4 and K added did not exceed the fixing capacity observed under wet conditions. However, when the amount added to soils to be subjected to oven drying exceeded the fixing capacity established for soils under wet conditions, NH 4 and K were fixed without a further reduction in the cation exchange capacity, indicating the occurrence of a fixation process or processes not associated with the cation exchange capacity.