Dynamics of soil organic carbon mineralization and enzyme activities after two months and six years of biochar addition

Applying biochar to agricultural soils has been proposed as a means of sequestering carbon while simultaneously enhancing soil health and agricultural sustainability. While, our understanding of the long-term effects of biochar on soil organic carbon mineralization and enzyme activities under field conditions is limited. In our study, soil samples, which were improved by biochar after two months and six years, were collected from biochar-amended treatments with seven biochar application rates (0, 2.5, 5, 10, 20, 30, and 40 t ha−1, respectively) in upland red soil. The results showed that the soil chemical properties (available P, pH, soil organic carbon, total nitrogen, and C/N ratio) after two months of biochar addition increased more significantly than those after six years of biochar addition. The cumulative soil organic carbon mineralization (Cm) was increased rapidly at first and then decreased gradually and finally flattened out in the late incubation. The Cm/SOC ratios were significantly lower in C1 to C6 treatments than in C0 treatment. High application rates (40 t ha−1) of biochar inhibited the carbon mineralization, while the effects diminished after six years of biochar addition. The multiple linear model and correlation analysis suggested that the effects of invertase activity and total nitrogen on Cm were more significant than other indexes.