Increasing doses of K were applied to 3 fields for eight years (1975-1983) conducted to obtain four potassium levels in soil (very poor, poor, medium rich and rich). Four doses of K (0, 70, 140, 280 kg K/ha) were applied on each of K soil level in 1983-1988, and after-wards. Residual effects of K were studied. Since 1975 3 corps (barley s., coksfoot, potatoes) on 3 fields crop rotation were grown every year. The influence of the above treatments on K exchange and K fixed in soil, yields, uptake of K by plants and K balance were studied. The similar K level in soil has been observed for many years, if negative K balance has not exceeded 50 kg K/ha/year. The increase of K exchanged is observed when potassium fertilization was provided for six years with the dose of 140 or higher kg K per hectare. After three year period without any potassium fertilization, yields of plants, K content in plant and soil on plots previously fertilized with high K dose, were still higher.