Do different land use changes in a deciduous forest ecosystem result in alterations in soil organic C and total N stocks?

Aims: This study sought to evaluate how soil organic carbon (SOC) and total nitrogen (STN) stocks vary following the conversion of a deciduous natural forest (DNF) to a paddy rice farm (PRF), a seventy-year-old Pinus koraiensis monoculture (CP70), a mixed forest (MF) plantation, and a P. koraiensis monoculture resulting from the re-plantation of a portion of the CP70 attacked by bugs. Methods: Soil samples (0–30 cm) were collected from DNF, PRF, CP7, CP70 and MF in the Gwangneung experimental site located in Gyeonggi-do (South Korea), and analyzed for bulk density, pH, SOC, STN content and stocks (0–30 cm). Results: The conversion of DNF into PRF showed 23.9% SOC stocks and 54.5% STN stocks increases. However, there were no significant changes in STN or SOC stocks after DNF was reforested for seven or 70 years or when PRF was reforested to MF. Conclusions: The conversion of a DNF to a PRF increased the SOC and STN stock, which might be due to over 63 years’ fertilizations with urea and diammonium phosphate, but reforestation with a P. koraiensis monoculture for 70 years and/or mixed forest was enough time to restore SOC and STN stocks to natural levels.