Carbon and nitrogen dynamics as affected by land-use and management change from original rice paddies to orchard, wetland, parking area and uplands in a mountain village located in Shonai region, Northeast Japan

This study investigated the effect of land-use and management change (LUMC) on carbon (C) and nitrogen (N) dynamics after 15-40 years. LUMC constituted change from rice paddies to chestnut orchard, wetland, and buckwheat upland fields in Shonai region, Yamagata Prefecture, Northeast Japan. Soil samples were collected from the top - (0-15 cm) and sub-layers (15-30 cm) for analysis of soil organic C (SOC) and its delta C-13 value, total N (TN), and their stocks. C decomposition (Dec-C) and net N mineralization (Net Min-N) were determined according to the production of CO2 and NH4+ + NO3- by aerobic incubation and CO2 + CH4 and NH4+ by anaerobic incubation, respectively. The results reveal that 40 years after change from rice paddy to orchard and wetland, the SOC and TN contents in the top-layer were not significantly altered. However, in buckwheat upland fields and in the parking area where vegetation was absent, the SOC content decreased significantly. Conversion of rice paddies to amur silver grass wetland altered the soil delta C-13 the most, leading to an increase of 5.1 parts per thousand and 2.9 parts per thousand for the top - and sub-layers, respectively. In general, the incubation experiment results revealed that a change to orchard and wetland did not significantly decrease the Dec-C and Net Min-N. Whereas, the change from rice paddies to parking area significantly decreased the Dec-C and Net Min-N in both aerobic and anaerobic conditions. We conclude that LUMC over decades had various effects on the SOC and TN contents and stocks as well as their mineralization potentials.