Soil carbon and nitrogen dynamics during conversion of agricultural lands to natural vegetation in central Korea

Changes in land use can affect the distribution and cycling of soil organic matter and nutrients. Soil organic carbon (C) and nitrogen (N) concentrations, soil CO₂ evolution, litter decomposition, and soil N availability under the three types of conversion of agricultural lands to natural vegetation (rice field conversion to forest, crop field conversion to shrub, and indigenous forest) in central Korea after 20 years of fallow were compared. There was no significant change in soil organic C and N concentrations among the three types at the three soil depths, and soil organic C and N increases were confined to the topsoil (0 - 10 cm). Soil CO₂ evolution tracked seasonal soil temperature, however, there was no difference among conversion types. Annual soil CO₂ evolution (Mg CO₂/ha/yr) was 36.0 ± 3.7 for the rice field conversion to forest site, 33.8 ± 4.1 for the crop field conversion to shrub site, and 40.7 ± 4.1 for the indigenous forest site, respectively. After decomposing for one year, 55.8% for the rice field conversion site, 64.9% for the crop field conversion site, and 66.3% for the indigenous forest site of the original leaf litter mass remained. The soil moisture condition seemed to limit the rate of decomposition in the study area. Resin NO₃ ^- -N concentration was higher at the rice field conversion site.