Biological CO2 cycle and organic carbon balance in maize (Zea mays) – soybean (Glycine hispida (Moench) Maxim.) agrocenosis in sod-podzolic soil

Topicality. Today, the search for ways to accumulate organic carbon and restore soil fertility, as well as increase crop yield, is a topical issue for the sod-podzolic soils of Western Polissia. Purpose. To determine the intensity of CO2 emission and the organic carbon balance on sod-podzolic soil at different fertilizer rates in the maize-soybean link against the background of chemical amelioration with incorporation of by-products. Methods. We used such methods as a stationary field trial, comparative and calculation method to determine the accumulated and emitted CO2 by plants, analytical and calculation methods to determine the organic carbon balance. Results. The CO2 emissions from organic matter mineralization amounted to 5.01–5.45 t/ha by the recommended fertilizer rate and calculated by the normative method on the background of dolomite and limestone powder, which was 23.4–34.2 % higher than the control (without fertilizers). The CO2 emission into the atmosphere through plant mass mineralization, depending on fertilization and chemical amelioration, was in the range of 18.6–24.7 t/ha and exceeded the control (without fertilizers) and the background of 1.0 Hh (hydrolytic acidity) CaMg(CO3)2 by 1.2–2.0 times, which is associated with improved soil conditions, higher by-products mass and CO2 accumulation by plants. The highest amount of CO2 was accumulated by maize (64.8–65.0 t/ha) and soybean (15.0–15.8 t/ha) at combination of the fertilizer rate calculated by the normative method with microfertilizers on the background of dolomite flour. The application of calculated fertilizer rates on the background of 1.0 Hh CaMg(CO3)2 provided an advantage in the formation of organic carbon in the soil, which formed a positive balance of 0.12 and 0.15 t/ha. In the variant without fertilizers and chemical amelioration, the ratio of total CO2 emissions into the atmosphere per 1 t of grain yield in the maize-soybean link was 4.65 and 4.62 units, while the application of the fertilizer rate calculated by the normative method against the background of 1.0 Hh CaMg(CO3)2 decreased to 3.78 and 3.89 units, respectively. Conclusions. For increasing the maize and soybean productivity on sod-podzolic loamy sandy soil, incorporation of plant mass into the soil with applying the fertiliser rates calculated by the standard method against the background of 1.0 Nh CaMg(CO3)2 is an effective method to control soil degradation that ensures the inclusion of additional organic carbon into the cycle, which is aimed at its fixation by forming a deficit-free balance of 0.12 and 0.15 t/ha. Key words: emission, organic carbon, productivity, fertilization, land amelioration, plant mass