Objective The paper aimed to explore the effects of tillage methods on soil organic carbon content and storage in the black soil area at the southern foot of the Daxing'an mountains, which has important guiding significance for the selection of suitable tillage methods and scientific management of carbon (C) pool in this region.

Method The study was based on the tillage positioning experiment conducted in 2018 at the test base in Arong Banner, Hulunbuir. The treatments of deep tillage with straw returning (DTS), deep loosening and shallow with straw returning (DSS), subsoiling tillage with straw returning (STS), heavy harrowing straw returning (SHS), rotary tillage with straw returning (RTS), and no-tillage straw returning (NTS), with shallow tillage without straw returning (CK) were set up to conduct field experiment. The effects of tillage methods on soil bulk density, porosity, organic C content, organic C storage (equal mass method), organic C stratification rate and maize yield of seven treatments were systematically analyzed during the mature period of maize in 2020 and 2021.

Result ① The bulk density of 0 - 60 cm soil increased with the deepening of the soil layer, and the change trend of total porosity was opposite. Compared with CK, the decrease of 0 - 60 cm soil bulk density under DTS treatment was 4.41% to 9.42%. The growth of total porosity was 3.59% - 11.09%. The bulk density of 10 - 60 cm soil was reduced best by DTS. ② All tillage methods under straw returning could increase soil organic C content in different degrees. In 0 - 20 cm soil layer, compared with CK, the soil organic C content of each tillage method under straw returning was significantly increased by 4.38% - 22.62% and 7.50% - 32.14% in all soil layers in 2020 and 2021, respectively. The soil organic C content of DSS treatment was the highest. In the 20 - 100 cm soil layer, the soil organic C content of DTS treatment was the highest, followed by that under DSS treatment. Compared with CK, the soil organic C content was significantly increased in 2020 and 2021, with an increase of 25.61% - 109.44% and 20.00% - 109.86%, respectively. The organic C stratification rate continuously increased as the soil layer deepens, with DTS treatment having the best effect on reducing soil organic C stratification rate, followed by DSS, which helps to evenly distribute organic C vertically and prevent nutrient accumulation on the surface. Moreover, DSS and DTS have higher organic C storage than other treatments, which is conducive to soil C pool management. ③ Compared with CK, all tillage treatments except for NTS could increase maize yield. In 2020, DSS treatment had the highest the economic and biological yield of maize, with an increase of 0.91% - 40.84% compared to other treatments, and a significant increase of 7.45% - 72.95% in maize biological yield. In 2021, DTS treatment had the highest economic and biological yield of maize, followed by DSS treatment. Compared with other treatments, the maize biological yield of DTS treatment significantly increased by 15.81% to 55.07%.

Conclusion The two tillage methods of deep tillage with straw returning and deep loosening and shallow with straw returning in black soil area are more beneficial for enhancing soil physical structure, increasing organic C pool storage and maize yield.