Soil carbon dynamic characteristics of coal gangue-filled reclaimed cropland and forest land under time series

In order to clarify the intrinsic mechanism between soil quality and soil carbon cycling after reclamation and to reveal the characteristic patterns of carbon dynamics of reclaimed soils under time series, the cultivated soils of 3, 6, 9 and 12 a reclaimed Dongtan mine area in Zoucheng, Shandong Province and the forested soils of 3 a and 12 a reclaimed were selected for this study, and the normal cultivated and forested soils within the mine area that were not affected by the collapse were used as controls. Soil carbon dynamics characteristics of reclaimed reconstructed soils under two different utilization methods of cropland and forest land under time series and its correlation relationship with soil physicochemical properties were investigated by field sampling and testing soil total carbon (TC), total nitrogen (TN), soil organic carbon (SOC), soil microbial quantity carbon (MBC) and soil physicochemical properties (pH, AN, AP).The results of the study showed that the soil organic carbon content of both cultivated land and forest land after reclamation increased gradually with the increase of reclamation time, and compared with the cultivated land and forest land after reclamation for 3 a and 12 a, the soil organic carbon content of cultivated land at all soil depths was higher than that of forest land soil at the corresponding depths; the organic carbon content of cultivated land soil 0-20 cm after reclamation for 12 a was not significantly different from that of the control, and the forest land soil 40-60 cm after reclamation for 12 a could reach the control level. The organic carbon content of 40-60 cm of forest soils reclaimed for 12 a was not significantly different from that of the control. The total carbon content of both cropland and forest soils was higher than the control at all reclamation years, which was related to the higher proportion of soil inorganic carbon content in the reclaimed soils.The soil microbial carbon content of cultivated soils was significantly higher than that of forested soils in the same reclamation period, and the rate of increase was faster; the soil microbial carbon content of cultivated soils was no longer significantly different from that of the control at 9 a of reclamation, while the soil microbial carbon content of cultivated soils reached 362.59 mg/kg at 12 a of reclamation, which was significantly higher than that of the control. The soil microbial carbon content of the forest land was 110.94 mg/kg, which was still significantly lower than that of the control. The trends of soil microbial entropy of cultivated land and its soil microbial carbon content after reclamation were similar, both showing a gradual increase.The microbial entropy of cultivated soils at 6, 9 and 12 a of reclamation were significantly higher than the control; the microbial entropy of forest soils at 3 a and 12 a of reclamation were significantly lower than the control. Reclamation soil SOC was highly significantly positively correlated with MBC, TN, and AN (p< 0.01), significantly positively correlated withq(MBC) and AP (p< 0.05), and significantly negatively correlated with pH (p< 0.05); MBC was highly significantly positively correlated with TN and AN (p< 0.01), significantly positively correlated withq(MBC) and AP (p< 0.05), and significantly correlated with TC pH showed highly significant negative correlations with AN and AP (p< 0.01) and significant negative correlations with TN (p< 0.05). The main conclusion was that along with the duration of reclamation, soil organic carbon and microbial carbon contents accumulated and recovered to different degrees under both land use methods after reclamation, and reasonable agricultural farming activities after reclamation contributed more to the continuous improvement of soil quality.