Driving factors of cultivated land soil organic carbon density change rate in Middle-Lower Reaches of the Yangtze River Region

Agricultural production emission is responsible for 23% of all anthropogenic greenhouse gas emissions in China in recent years. Particularly, a large number of parts are accounted for the carbon dioxide equivalent of China’s greenhouse gas emissions in global emissions. Among them, arable land also serves as a significant carbon sink. It is also crucial to explore novel techniques for soil organic carbon sequestration in cultivated land. Numerous agricultural strategies have been proposed to promote carbon sequestration and carbon sinks in cultivated land in modern agriculture. At the same time, future research can be required to determine the primary driving factors, and then to systematically evaluate the soil carbon sequestration. However, it is still lacking on systematic research on the characteristics and driving factors of soil organic carbon stock in cultivated land. Taking the middle-lower reaches of the Yangtze River Region (the typically agricultural regions of China) as the study areas, this study aims to achieve carbon sequestration and sinks in great agriculture. The observation data of organic carbon stock was collected from 59 positioning experimental stations. The soil organic carbon density change rate was also quantified in the different cultivated land. A random forest (RF) model was then used to explore the driving factors on the soil organic carbon density change rate. The results show that: 1) The variation ranges of soil organic carbon density change rate were −1 548.15-3 577.10 kg/(hm²·a) and −261.89-3 245.01 kg/(hm²·a), respectively, in the paddy fields and dry lands. But there was no significant difference between the paddy fields and dry lands. Besides, different crop rotation patterns posed different potentials for organic carbon sequestration. Specifically, the rice-wheat and oilseed rape-cotton rotation patterns performed better than the rest. 2) There was a great effect of the organic fertilizer nitrogen content, soil pH value, chemical fertilizer nitrogen, and straw nitrogen content on the soil organic carbon density change rate in the paddy field. The mean decrease accuracy (MDA) values were 0.49, 0.32, 0.23, and 0.15, respectively. By contrast, some effect was found in the mean annual precipitation, soil organic carbon content, mean annual temperature, multiple cropping index, paddy, and dry crop rotation. Furthermore, the organic and chemical fertilizer nitrogen content shared a great effect on the soil organic carbon density change rate in the dryland. The MDA values were 0.98, and 0.10, respectively. There were no major factors in the soil pH value, mean annual temperature, clay fraction, multiple cropping index, and straw nitrogen content. 3) Partial dependence analysis showed that the increasing soil organic carbon stock in the paddy fields tended to occur when combining the application of organic and chemical fertilizer, or the soil pH value to the neutral, and the straw returning to the field. The application of organic and chemical fertilizer tended to increase the organic carbon stock in the drylands. The soil organic carbon stock increased in cultivated land when the proportion of organic fertilizer nitrogen accounted for 10% to 30% of the total nitrogen fertilizer. Therefore, it was recommended that the soil pH value should be reasonably regulated to combine the application of organic and chemical fertilizers for conservation and carbon sequestration in the paddy fields. Therefore, the neutral pH value can be expected to achieve cultivated land carbon sequestration and high crop yield in tandem. This finding can provide a strong reference for the soil organic carbon sequestration and sink enhancement in cultivated land in the middle-lower reaches of the Yangtze River Region.