Land Use Alters the Plant-Derived Carbon and Nitrogen Pools in Terraced Rice Paddies in a Mountain Village

In Japan, terraced paddies in mountain villages are symbolic of the traditional landscape, but they are gradually being abandoned. To compare plant-derived C and N among land uses, we compared adjacent forest floor (FF), agricultural paddy (AP), and post-agricultural paddy (PP) sites. Long-term litter accumulation could explain the significantly higher litter C and belowground biomass C in FF than in AP and PP. The low-density-fraction (LF) soil C was significantly higher in FF than in PP and better reflected land use than the whole-soil C. The AP soil held more N than FF and PP at 20–30 cm, associated with higher LF soil N. Periodic tillage in AP maintains the LF soil N, but N supplied to the surface soil reduced with depth following abandonment. Differences in recycling of organic matter and nutrients among land uses are crucial to plant-derived C and N contents of soil