SummaryIn the various types of loess soils, represented in the form of a catena, migration and alterations of 2: 1 layer‐minerals are the essential cause of a differentiating influence on the phenomena of K‐fixation. The K‐fixation is much greater in river alluvial than in loess soils. The high values of fixation are due to the large contents of clay consisting mainly of expanded 2:1 layer minerals. The river alluvial soils in the delta generally fix much more K than those in the region of the headwaters. By means of pot experiments the alterations of exchangeable‐ and fixed‐K have been examined in their dependence on the varying degree of soil exhaustion by cropping. Although an alluvial soil with K fertilizer showed a large amount of exchangeable‐K, fixed‐K partly diffused into the exchangeable form, and hence precise distinction between exchangeable‐ and fixed‐K was not possible. In contrast, the quantity of exchangeable‐K in the B horizon of a grey‐brown podzolic soil had to be exhausted to the level of the unfertilized soil before fixed‐K was released. In this case the difference in binding strength between exchangeable and fixed‐K could be clearly shown. The release of non‐exchangeable‐K from unfertilized soils was accompanied by a corresponding increase of fixation. Thus, when fertilizer is omitted, charges are set free in the 2:1 layer mineral which will fix an