The crop rotation productivity depends on the crops and chemicals used, especially fertilizers. Cultivation of crops makes it possible to obtain environmentally safe products due to biologically correctly selected predecessors and with the correct alternation of crops in space and time. This allows for savings in plant protection products and differentiated use of fertilizers. Based on the results of 28-year research into the yield and productivity of crop rotation with the use of various doses of fertilizers, the regularities of changes in the content of mobile phosphorus and exchangeable potassium in the soddy-podzolic medium loamy soil of Vologda Oblast were revealed, and regression models that reflect their relationship with the productivity of crop rotation were built. The results made it possible to build a non-linear regression model that reflects quantitative features of the dependence of crop rotation productivity on the levels of mobile phosphorus and exchangeable potassium. With an increase in the content of mobile elements in the soil in the case of mobile phosphorus, the productivity of crop rotation will increase with a slight slowdown with each single dose, and in the case of exchangeable potassium it will increase evenly.