Observation study on GHG emissions from ratoon rice field transformed from the typical single-cropping rice fields

To investigate the greenhouse gas emission characteristics of promoting ratoon rice retention in typical single-season rice areas and regions with insufficient thermal conditions for double cropping, a one-year in-situ field study on greenhouse gas emissions was conducted in the Taihu Basin using static chambers and gas chromatography. Six cropping systems were examined: rice-wheat (RW), rice-oilseed rape (RO), rice-cabbage (RC), rice-Astragalus. (RA), rice-fallow (RF), and rice-ratoon rice- Astragalus. (Rr). Results showed that the annual CH₄ emissions for single-season rice systems (RW, RO, RC, RF, RA) ranged from 43.8 to 135 kg (CH₄)∙hm⁻², while that of the ratoon rice system (Rr) was 541 kg (CH₄)∙hm⁻². Annual N₂O emissions ranged from 8.16 to 19.7 kg (N)∙hm⁻² for single-season rice systems and 4.30 kg (N)∙hm⁻² for the ratoon rice system. Annual yields were 6.99 to 11.0 t∙hm⁻² for single-season rice systems and 14.1 t∙hm⁻² for the ratoon rice system. Compared to single-season rice systems, the ratoon rice system showed significantly higher annual CH₄ emissions, increasing by 3.01 to 11.4 times, and significantly lower annual N₂O emissions, decreasing by 47.3% to 78.1%. Total greenhouse gas emissions (TGHG) increased significantly by 64.1% to 240%, and annual yields increased significantly by 27.5% to 102%. Greenhouse gas emission intensity (GHGI) increased by 14.7% to 68.7%. The straw return in the main season under the Rr system significantly increased CH₄ emissions during the ratoon season, leading to higher TGHG in the ratoon rice system compared to the five single-season rice systems. In conclusion, ratoon rice retention in typical single-season rice areas can significantly increase total crop yield but also raises GHGI. It is therefore recommended to strengthen water management in ratoon rice fields and delay straw return until after the ratoon harvest to reduce CH₄ emissions, achieving the dual goals of high yield and reduced emissions.