Sequestration capacity of crop rotation with long rotation in the central part of the Forest Steppe

Abstract

Goal. To establish regularities in the formation of CO2 emission volumes by agrophytocenoses of 7–10 field crop rotations and deposition of carbon dioxide in the system «soil — atmosphere — crops» to assess the potential sequestration capacity of agrocenoses of crop rotations with a long rotation for the conditions of the central part of the Forest Steppe of Ukraine. Methods. Field, agrochemical (selection of samples and determination of total humus), statistical calculation (to justify the reliability of the results and develop statistical models of relationships). The research was carried out on the Drabiv experimental field in a stationary experiment, which was established in 1967 and included 29 different crop rotations. Results. During crop rotation with a long rotation, the content and reserves of total humus, humus carbon, and in terms of Cg and Corg-CO2 reserves (in terms of deposited CO2) in the 0–20 cm layer were higher by 0.14 and 0.08%, respectively, than under short crop rotations, in the soil layer of 20–30 cm — by 0.13 and 0.07%, respectively, according to the content of humus Cg, while the reserves of Cg and Corg-CO2 were equal. In the 0–30 cm layer, for 7–10 field crop rotations, the humus content was higher by 0.13%, Cg by 0.08%, Cg and Corg-CO2 reserves — by 15.6 t/ha compared to crop rotations with a short rotation. For 7–10 field crop rotations, the value of the parameters of the humus state was higher on the median compared to the average value and tended to the upper typical value of the humus content in the normalized interval of values, which indicated an increase in the content and stocks of humus. As an evaluation criterion of the sequestration capacity and productivity of crop rotation, they adopted the ratio between the deposition of Corg-CO2 in the main products to C-CO2 from the mineralization of humus and by-products. It was found that CO2 from mineralization varied within 18–31 t/ha. Conclusions. Deposition of Corg-CO2 for 7–10 field crop rotations was 31–54 t/ha. The ratio of Corg-CO2 to Cmin-CO2, which should exceed 1.5:1 in favor of the deposition of organic carbon in the main products and humus, was adopted as an evaluation criterion of the sequestration capacity and productivity. In the general series of crop rotations for 7–10 field crop rotations, the most effective were: No. 5 (50% — cereals, 20 — row crops, 30 — annual grasses); No. 9 (50% — cereals, 10 — legumes, 20 — row crops, 20% — annual grasses); No. 2 (50% — cereals, 20 — technical, 20 — peas, 10% — annual grasses); No. 17 (40% — cereals, 20 — legumes, 30 — technical, 10% — annual grasses).