Soil samples for conventional management (CM) and intensive management (IM) practices were taken over a year at2-month intervals to determine the effect of management practices on soil organic carbon (SOC) and to quantify seasonal dynamics in SOC for bamboo (Phyllostachys pubescens Mazel ex H. de Lehaie) stands. The results with IM compared to CM showed large decreases in total organic carbon (TOC), microbial biomass carbon (MBC), water-soluble organic carbon (WSOC), and the MBC/TOC ratio in the soils. With all IM plots in the 0-20 cm depth across sampling periods,average decreases compared with CM were: TOC, 12.1%; MBC, 26.1%; WSOC, 29.3%; the MBC/TOC ratio, 16.1%;and the WSOC/TOC ratio, 20.0%. Due to seasonal changes of climate, seasonal variations were observed in MBC and WSOC. Soil MBC in the 0-20 cm depth in September compared to May were 122.9% greater for CM and 57.6% greater for IM. However, due primarily to soil temperature, soil MBC was higher during the July to November period, whereas because of soil moisture, WSOC was lower in July and January. This study revealed that intensive management in bamboo plantations depleted the soil C pool; therefore, soil quality with IM should be improved through application of organic manures.