Five representative soils with contrasting physical, chemical, and mineralogical characteristics from the Chaouia and Gharb regions of northwestern Morocco were selected for a study of the effects of wetting and drying cycles (W‐D), temperature, amount of K+added, and extracting solution on the determination of K‐fixation. With drying at 40°C and the use of of 0.2 M CaCl2for K+extractions, the measured amount of K+fixed increased with increased number of W‐D cycles when high quantities of Kwereadded. The drying, however, caused release of K+when no or small amounts of K+were added even for soils not containing mica (illite). With 2 W‐D cycles, measured K+fixation decreased with increasing drying temperature from 40oC to 100oC regardless of the extracting solution when the calculated fixation was based on the initial extractable K+rather than the quantity extracted from the zero treatment after wetting and drying. Also, significant differences in K+fixation existed between extracting solutions at any given temperature. Because of the different drying temperatures and extracting salts used it is difficult to compare results of K+fixation reported in different studies. Frequent changes in temperature and soil water content during the growing season in Mediterranean climates may have an important influence on K+availability.