Simulated Soil Organic Carbon Density Changes from 1980 to 2016 in Shandong Province Dry Farmlands Using the CENTURY Model

The changes in cultivated soil organic carbon (SOC) have significant effects on soil fertility and atmospheric carbon dioxide (CO 2 ) concentration. Shandong Province is an important agricultural and grain production area in China. Dry farmland accounts for 74.15% of the province’s area, so studies on dynamic SOC changes would be helpful to understand its contribution to the Chinese national carbon (C) inventory. Using the spatial overlay analysis of the soil layer (1:10,000,000) and the land use layer (1:10,000,000), 2329 dry farmland soil polygons were obtained to drive the CENTURY model to simulate SOC dynamics in Shandong Province from the period 1980 to 2016. The results showed that the CENTURY model can be used to simulate the dry farmland SOC in Shandong Province. From the period 1980 to 2016, the soil organic carbon storage (SOCS) and soil organic carbon density (SOCD) showed an initial increase and then decreased, especially after reaching a maximum in 2009. In 2016, the SOCS was 290.58 × 10 6 t, an increase of 26.99 × 10 6 t compared with 1980. SOCD in the dry farmland increased from 23.69 t C ha −1 in 1980 to 25.94 t C ha −1 in 2016. The dry farmland of Shandong Province was a C sink from 1980 to 2016. Among the four soil orders, inceptisols SOCD dominated, and accounted for 47.81% of the dry farmland, followed by >entisols > vertisols > alfisols. Entisols SOCD growth rate was the highest (0.23 t C ha −1 year −1 ). Compared to 1980, SOCD in 2016 showed an increasing trend in the northeast, northwest and southeast regions, while it followed a downward trend in the southwest.