Abstract <p>The effect of long-term application of increasing doses of mineral (from N90P75K100 to N360P300K400) and organic (cattle manure, from 25 to 100 t/ha) fertilizers on the fertility of gray forest soil has been studied in a micro-plot experiment. Over 9 years, 0.81–3.24 t/ha of nitrogen, 0.68–2.70 t/ha of P₂O₅, and 0.90–3.60 t/ha of K₂O were applied with mineral fertilizers. The manure was supplied with 43–173 t/ha of dry matter, 16–65 t/ha of C_org, 0.85–3.41 t/ha of N_tot, 0.65–2.59 t/ha of P₂O₅, and 0.86-3.46 t/ha of K₂O. On average, the mineral fertilizer system was 29% more effective than the organic one with respect to the yield. At extreme doses (N360P300K400 and 100 t/ha of cattle manure), mineral fertilizers reduced crop productivity more significantly than organic fertilizers. A direct linear relationship has been found between doses of mineral and organic fertilizers and the increase in the content of available P₂O₅ and K₂O in the soil. Application of extreme doses of fertilizers has not led to the saturation of the soil with available forms of phosphorus and potassium. Long-term application of organic fertilizers has increased the soil pH(KCi) by 0.4–1.3 units and that of mineral fertilizers has decreased it by 0.8–1.4 units. Annual application of mineral fertilizers has increased the soil C_org content by an average of 0.02–0.04% per year and that of organic fertilizers by an average of 0.08–0.17% per year. Manure application at a dose of 100 t/ha over the 9 years has led to the saturation of the soil with organic carbon. The C:N ratio in the soil under the mineral fertilizer system has decreased, while it has increased under the organic system. An approach to calculating the carbon sequestration efficiency for assessing different agronomic practices is proposed. It is shown that the carbon sequestration efficiency of organic fertilizers was 15% higher than that of mineral fertilizers.</p>