Anthropogenic soil management performs an important role in increasing soil organic carbon content in northeastern China: A meta-analysis

The black soil region of northeastern China stores large amounts of soil organic carbon (SOC), so understanding the changes of SOC content and its influencing factors is necessary for understanding the global carbon cycle. These changes, however, vary with tillage, fertilization, cropping system and other soil management methods. Synthesizing and evaluating these studies is necessary to understand the mechanism of change in SOC content and for predicting future SOC content in cropland ecosystems in this region. We therefore used a meta-analysis of 666 observations from 91 publications to clarify the effects of type of soil management (tillage, fertilization and cropping system) on SOC content. The results indicated that soil management significantly increased SOC content by 8.3% compared to the initial content. SOC content increased significantly by 16.2% with organic fertilizer (OF) and by 19.6% with organic fertilizer combined with chemical fertilizer but decreased significantly by 3.9% without fertilization compared to the initial experiments (P < 0.05). SOC content increased significantly by 9.3% and 5.6% under conventional and deep tillage, respectively. SOC content increased significantly by 13.5% and 4.0% under crop monoculturing and crop rotation, respectively. The effect size of SOC content was significantly correlated with mean annual precipitation, mean annual temperature, the contents of clay and soil nutrients. The results will help us to understand the responses of SOC content to various types of soil management and to identify the most suitable soil management type in northeastern China.