Opencast coal mining results in high loss of soil organic carbon (SOC), which may be restored via recultivation. Common strategies include liming, topsoil application, and phytoremediation. It remains unclear, however, which parameters determine the effectiveness of these varying recultivation strategies especially regarding SOC sequestration. This meta-analysis analyses the effect of varying recultivation strategies on SOC sequestration under different climate and soil conditions (pH, texture, depth) as well as in relation to time, based on 404 data entries from 51 studies. All included climatic regions recorded increases in SOC stocks, with tropical soils showing the highest potential for relative gains at up to 637%. We demonstrate that loamy soils sequester twice as much newly introduced SOC than sand. Strategy-wise, the highest mean rate of SOC sequestration is achieved by forest after topsoil application (3.9 Mg ha−1 a−1), agriculture after topsoil application (2.3 Mg ha−1 a−1), and agriculture with topsoil and fertiliser application (1.9 Mg ha−1 a−1) with a response ratio of 304%, 281%, and 218%, respectively. Soils analysed to less then 40 cm depth show higher SOC sequestration rates (< 10 cm: 0.6 Mg ha−1 a−1, < 20 cm: 1.0 Mg ha−1 a−1, and 20–40 cm: 0.4 Mg ha−1 a−1; response ratio of 123%, 68%, and 73%, respectively) than those analysed to a depth of 41–80 cm (0.1 Mg ha−1 a−1; response ratio of 6%). In terms of pH, strongly acidic soils (pH < 4.5) and alkaline conditions (pH > 7) offer the most beneficial environment for SOC sequestration at 0.4 Mg ha−1 a−1 and 0.8 Mg ha−1 a−1, respectively (185% and 273% response). Given comparable SOC sequestration potentials of forest after topsoil application, agriculture without amendments, and forest without amendments, we recommend to weigh these strategies against each other. Potentially decisive aspects are short- vs. long-term economic gains, food security concerns, and—in case of agriculture—the risk of overintensification leading to losses in SOC. Our data suggests that amendments exert considerable influence on SOC sequestration and need to be introduced under careful consideration.

Opencast coal mining results in high loss of soil organic carbon (SOC), which may be restored via recultivation. Common methods include liming, topsoil application, and phytoremediation. It remains unclear, however, which parameters determine the effectiveness of varying recultivation strategies especially regarding SOC sequestration. We, therefore, analysed the relationship between SOC stock changes in abandoned coal mines and the recultivation method, soil properties (pH, texture, depth), climate, and time under recultivation in 51 studies (404 data entries). All included climatic regions recorded increases in SOC stocks, with tropical soils showing the highest potential for relative gains of up to 468%. With respect to soil texture, clay content is the main factor promoting SOC sequestration. Strategy-wise, the largest positive effect was achieved by forest with liming (1.5 Mg ha− 1 a− 1), fallow after topsoil and fertiliser addition (1.1 Mg ha− 1 a− 1), agriculture after topsoil addition (1.0 Mg ha− 1 a− 1), and forest with fertiliser (1.0 Mg ha− 1 a− 1) with a response ratio of 35%, 58%, 140%, and 48%, respectively. Soil depths < 10 cm, < 20 cm, and 21–40 cm stored more SOC (0.6 Mg ha− 1 a− 1, 1.0 Mg ha− 1 a− 1, and 0.4 Mg ha− 1 a− 1; response ratio of 123%, 68%, and 73%, respectively) than soils at a depth of 41–80 cm (0.1 Mg ha− 1 a− 1; response ratio of 6%). In terms of pH, strongly acidic soils (pH < 4.5) and alkaline conditions (pH > 7) offered the most beneficial environment for SOC sequestration at 0.4 Mg ha− 1 a− 1 and 0.8 Mg ha− 1 a− 1, respectively (44% and 67% response).

&lt;p&gt;The decline in organic carbon (OC) stocks after conversion from grassland to cropland under conventional soil tillage practices was 24-32% for American prairie soils. The respective decreases in OC stocks ranged from 27% to more than 40% for steppe soils of the European part of Russia and was about 31% in semi-arid steppe soils of South Siberia. Here, we present results on the soil OC stocks in steppe soils of Northern Kazakhstan, which partly were converted to arable land over the last 60 to 90 years. We sampled soils by genetic horizons along a north-south transect, where precipitation increased towards north but negligible variation in temperature. Soil samples were analyzed for organic and inorganic carbon as well as bulk density.&lt;/p&gt;&lt;p&gt;Surprisingly, we found along the transect on average only 3.5% smaller OC stocks at 0-10 cm depth in arable than in natural soils. Even more astonishing, all arable soils tested had larger OC stocks in the layers beneath 10 cm depth than the natural steppe soils. On average, the OC stocks in 10-100 cm depth were 34% larger in soils under arable management than in natural steppe soils. We credit the enhanced deep soil accumulation of OC in arable soils of Northern Kazakhstan to colloidal translocation of OC-rich particles along vertical pores. The cause of the increased in colloidal transport under arable management is still under evaluation but appears connected to the clayey soil texture and the large abundance of expandable clay minerals. We conclude that despite of the intense land use and severe climatic conditions accumulation of subsoil carbon is possible even after many decades of cultivation history. Our findings stress the importance of considering whole soil profiles for analyzing the consequences of land use change on the net carbon balance of soils.&lt;/p&gt;