Effects of Flooded Rice Cultivation on Soil Organic Carbon and Active Organic Carbon Content: A Microcosm Experiment

Information on carbon (C) dynamics and allocation in plant–soil system is essential to understand the terrestrial C cycle. Our aims were to determine the effects of rice growth on soil organic carbon (SOC), dissolved organic carbon (DOC) and microbial biomass carbon (MBC) content. For this a pot microcosm experiment in growth chamber was conducted with soils planted or unplanted with rice. The experiment lasted for 80 days. The SOC content increased both in unplanted and rice-planted soils over the incubation period. The increasing amount of SOC in rice-planted soil was larger than that of in unplanted soil, indicating that growing rice on bulk soil enhanced the function of soil as a carbon poo1. The DOC enhanced significantly (P < 0.05) compared to the zero time (Day 0 (CK)) both in planted soils and unplanted soils during 80 days of incubation. The DOC concentrations in planted soils were much larger than that of unplanted soils, suggesting the release of soluble root exudates from rice roots. However, MBC declined both in unplanted soil and rice-planted soil after incubation for 80 days, compared with the start of experiment. The results suggest that MBC dynamics in rice soil are largely controlled by organic substances released from rice roots.