Optimization of potassium fertilizer rates applied to sugar beet on potassium-rich soils of the Central Chernozem zone

We tracked the effect and two-year aftereffect of potassium fertilizers with a single application under beet in rates of 70-240 kg∙ha-1 K2 O in six farming trails of the Central Federal District, conducted in the Voronezh and Lipetsk Regions with sugar beet on soils with increased and high soil potassium levels. The contribution of potassium to the yield increase on average over three years was 14-15%. The content of exchangeable potassium during the experiments corresponded to a higher level of potassium supply compared to the available form, by one or two classes. The use of the potassium balance indicator for calculating the rates of fertilizers applied is advisable in years favorable for crop development. Calculation of optimal rates of potassium fertilizers obtained using multicriteria estimation allows to consider 140 kg∙ha-1 K2 O with a possible increase to 210 kg∙ha-1 in years favorable for crop development as the optimal for application to sugar beet in the Voronezh Region, and from 210 to 280 kg∙ha-1 K2 O in the Lipetsk Region. A promising approach to determine potassium rates to jointly take into account the indicators of the effect and after-effect of fertilizers in terms of yield growth, 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 classes 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 methods for calculating rates of potassium fertilizers require both the correction of the proposed classes of potassium availability and the consideration of the emerging potassium balance.