Soil properties and carbon sequestration of afforested pastures in reclaimed minesoils of Ohio

Land-use change affects many soil properties, including soil organic carbon (SOC) pool, and the transfer of atmospheric CO2 to terrestrial landscapes. The objective of this study was to evaluate the effects of converting pastureland to Australian pine (Casuarina spp) and Black locust (Robinia pseudoacacia L) forest on selected soil physical and chemical properties and SOC sequestration in reclaimed minesoils (RMS) of southeastern Ohio. The study sites were surface mined for coal, reclaimed and managed as pasture, and then converted into woodland 10 yr before the present study. Soil pH and electrical conductivity (EC) were higher in the RMS than in a nearby undisturbed hardwood forest. Conversion to Australian pine decreased soil pH and EC in the top 20 cm. Bulk densities of the RMS ranged from 1.24 to 1.82 Mg m(-3), and only minor changes were observed in soil bulk density after land-use conversion. Mean weight diameter (MWD) and root biomass increased significantly (P < 0.05) with conversion of pasture to Australian pine or Black locust. In addition, aggregate stability was greater in RMS under hardwood forest than under pasture. Conversion to the Australian pine forest increased the SOC pool in the top 50 cm by 6 Mg ha(-1) (11%) in 10 yr. However, the N pool in the top 50 cm was not affected by the land-use conversion from pasture to Australian pine. Conversion to Black locust increased the SOC pool in the top 50 cm by 24 Mg ha(-1) (42%), while the N pool increased by 10% under Black locust in 10 yr. The increase in the SOC pool was accompanied by an increase in the C/N ratios and root biomass in both Australian pine and Black locust sites in the 20- to 50-cm depth. Establishment of tree plantation has a greater potential for SOC sequestration than pastures in the RMS.