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Recommended management practices (RMPs, e.g., manuring, no-tillage, crop residue return) can increase soil organic carbon (SOC), reduce greenhouse gas emissions, and maintain soil health in croplands. However, there is no consensus on how RMPs affect the SOC storage potential of cropland soils for climate change mitigation. Here, based on 2301 comparisons from 158 peer-reviewed papers, a meta-analysis was conducted to explore management-induced SOC stock changes and their variations under different conditions. The results show that SOC stocks in the 0–20 cm layer were increased by 31.8% when chemical fertilization combined with manure application was compared with no fertilizer; 9.98% when no-tillage was compared with plow tillage; and 10.84% when straw return was compared with removal. The RMPs favorably increased SOC stock in arid areas, and in alkaline and fine-textured soils. Initial SOC, carbon-nitrogen ratio, and experimental duration could also affect SOC storage. Compared with the initial SOC stock, RMPs increased the SOC sequestration potential by 2.6–4.5% in the 0–20 cm soil depth, indicating that these practices can help China achieve targets to increase SOC by 4.0‰. Hence, it is essential to implement RMPs for climate change mitigation and soil fertility improvement. • RMPs can increase SOC stock and mitigate climate change. • RMPs-induced SOC changes depend on local environmental conditions. • The SOC storage potentials were decreased with the increase of soil depth. • RMPs can achieve targets to increase SOC by 4.0‰ in Chinese croplands. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) is of great importance in the global carbon cycle. Distribution patterns of SOC in various regions of China constitute a nation-wide baseline for studies on soil carbon changes. This paper presents an integrated and multi-level study on SOC stock patterns of China, and presents baseline SOC stock estimates by great administrative regions, river watersheds, soil type regions and ecosystem. The assignment is done by means of a recently completed 1: 1,000,000 scale soil database of China, which is the most detailed and reliable one in China at the present time. SOC densities of 7292 soil profiles collected across China in the middle of the 1980s were calculated and then linked to corresponding polygons in a digital soil map, resulting in a SOC Density Map of China on a 1: 1,000,000 scale, and a 1km×1km grid map. Corresponding maps of administrative regions, river watersheds, soil types (ST), and ecosystems in China were also prepared with an identical resolution and coordinate control points, allowing GIS analyses. Results show that soils in China cover an area of 9.281×106 km2 in total, with a total SOC stock of 89.14Pg (1Pg=1015 g) and a mean SOC density of 96.0tC/ha. Confidence limits of the SOC stock and density in China are estimated as [89.23Pg, 89.08Pg] and [96.143tC/ha, 95.981tC/ha] at 95% probability, respectively. The largest total SOC stock (23.60Pg) is found in South-west China while the highest mean SOC density (181.9tC/ha) is found in north-east China. The total SOC stock and the mean SOC density in the Yangtze river watershed are 21.05Pg and 120.0tC/ha, respectively, while the corresponding figures in theYellow river watershed are 8.46Pg and 104.3tC/ha, respectively. The highest total SOC stocks are found in Inceptisols (34.39Pg) with SOC density of 102.8tC/ha. The lowest and highest mean SOC densities are found on Entisols (28.1tC/ha), and on Histosols (994.728.1tC/ha), repectively. Finally, the total SOC stock in shrub and forest ecosystem classes are 25.55 and 21.50Pg, respectively; the highest mean SOC density (209.9tC/ha) was recorded in the wetland ecosystem class and the lowest (29.0tC/ha) in the desert ecosystem class. Among five forest ecosystem types, Evergreen conifer forest stores the highest SOC stock (6.81Pg), and Deciduous conifer forest shows the highest SOC density (225.9tC/ha). Figures of SOC stocks stratified by Administrative regions, river watersheds, soil types and ecosystem types presented in the study may constitute national-wide baseline for studies of SOC stock changes in various regions in the future. [Copyright &y& Elsevier]