Abstract: The ratoon rice cultivation is important to stabilize rice production under the background of double rice system shifting to single rice system. To investigate the effects of ratoon rice cultivation on soil organic carbon (SOC) and soil fertility, we analyzed the differences of soil nutrients and chemical structure of SOC among single, double, and ratoon rice systems. Soil pH of ratoon rice field was significantly lower than that of single rice field, but no difference with double rice field. The contents of main nutrients in soils generally followed the order: double rice filed>ratoon rice field>single rice field. Accordingly, soil fertility index (SFI) of three rice systems was 0.66, 0.47, and 0.40, with significant difference among each other. The chemical structure of SOC was significantly different among the three rice cultivation systems. The proportion of soil Alkyl-C in ratoon rice field was significantly higher than that in single rice field but lower than that in double rice field. In contrast, the proportion of soil O-Alkyl-C in ratoon rice field was significantly lower than that in single rice field but higher than that in double rice field. The ratio of Alkyl-C/O-Alkyl-C under ratoon rice filed increased by 23.81% compared to single rice field, but decreased by 30.67% compared to double rice field. The Alkyl-C/O-Alkyl-C ratio was significantly and positively correlated with SOC content (R²=0.95, P<0.001) and SFI (R²=0.96, P<0.001). In conclusion, soil fertility of ratoon rice filed is higher than that of single rice field but lower than that of double rice field, which is closely related with fertilizer input, flooding period, and crop nutrient uptake.

Key words: cultivation pattern, ratoon rice, soil fertility, soil organic carbon, nuclear magnetic resonance.