Soil Carbon Content and Stable Isotope Ratio in Abandoned Agricultural Fields: Land Use Change from Paddy to Upland Grass in Higashi-Hiroshima, Japan

Abstract

The aim of this study was to investigate the cessation of cultivation act as a sink or source for belowground carbon pools in former paddy fields. We measured soil carbon content and stable carbon isotopic ratio (δ¹³C) in three abandoned agricultural fields in Higashi-Hiroshima, Japan. The fields were located within 0.20 km of one another and had been abandoned for 2, 5, or 10 years (2Y, 5Y, 10Y fields). The cessation of cultivation of agricultural fields was dominated by C₄ photosynthetic type grass. The return of carbon in grass litters to the soil caused the soil δ¹³C to increase after abandoned; thus, the soil δ¹³C value was lowest in the 2Y field (-24.2‰) and highest in the 10Y field (-22.1‰). While the large root biomass in fields after the long-term cessation of cultivation is a potential source of carbon input into the soil, soil carbon content was lower in the fields abandoned for longer. Land use change (from paddy to upland grasses) may lead to a decrease in the soil carbon content in the fields after abandonment in this area.