Abstract <p>We tracked the effect and 2-year aftereffect of potassium fertilizers with a one-time application under sugar beet at the rates of 70‒240 kg/ha K₂O in the Central Federal District in six farming trials conducted in Voronezh oblast and Lipetsk oblasts on soils with increased and high soil potassium supply. The contribution of potassium to the yield increase over 3 years averaged 14‒15%. The content of exchangeable potassium during trials accounted for a higher level of potassium supply compared to the mobile form, by one or two grades. The use of the potassium balance indicator is advisable for calculating the applied fertilizer rates in years favorable for the crop growth. Calculation of optimal rates of potassium fertilizers obtained using multicriteria assessment allows us to consider 140 kg/ha K₂O with a possible increase to 210 kg/ha in years favorable for crop growth optimal for application under sugar beet in Voronezh oblast, and from 210 to 280 kg/ha K₂O in Lipetsk oblast. A promising approach to determine potassium rates involves taking into account combination the indicators of the effect and aftereffect of fertilizers in yield increase, economic efficiency, and the possibility of achieving a positive balance. The use of calculations based on only one of the above criteria, as well as on grades or direct assessments of soil potassium supply levels based on standard methods, leads to a significant overestimation or underestimation of the results due to the temporal instability of the determined indicators. Existing calculation methods for rates of potassium fertilizers require both the correction of the existing grades of mobile potassium supply and the consideration of the potassium balance.</p>