Waterlogging accelerates the loss of soil organic carbon from abandoned paddy fields in the hilly terrain in subtropical China

Paddy soils have been widely recognized as important carbon sinks. However, paddy field abandonment is increasing in the hilly area in subtropical China. Soil waterlogging and weed burning are common practices in abandoned paddy fields, which could affect vegetation cover and carbon sequestration. An rice cultivation experiment was ceased in 2006, and four new treatments were applied as waterlogging (W), drainage (D), waterlogging combined with burning (WB), and drainage combined with burning (DB). Waterlogging altered the vegetation cover and caused an associated change in biomass. Paspalum paspaloides, Murdannia triquetra, and Bidens frondosa dominated W and WB plots, and Microstegium vimineum and Bidens frondosa dominated D and DB plots. Abandonment of paddy fields led to a rapid decrease in soil organic carbon (SOC), and waterlogging accelerates SOC loss which should be attributed mainly to alteration of the vegetation cover. Six years’ rice cultivation increased SOC content by 13.5% (2.4 g kg(−1)) on average. In contrast, six years’ abandonment reduced SOC content by 14.5% (3.0 g kg(−1)) on average. Decline rate of SOC was 0.38, 0.64, 0.30, and 0.65 g kg(−1) a(−1) for D, W, DB, and WB, respectively. Such results indicate a significant risk of SOC loss from abandoned paddy fields.