Drainage and tillage practices in the winter fallow season mitigate CH₄ and N₂O emissions from a double-rice field in China

Abstract. Traditional land management (no tillage, no drainage, NTND) during the winter fallow season results in substantial CH₄ and N₂O emissions from double-rice fields in China. A field experiment was conducted to investigate the effects of drainage and tillage during the winter fallow season on CH₄ and N₂O emissions and to develop mitigation options. The experiment had four treatments: NTND, NTD (drainage but no tillage), TND (tillage but no drainage), and TD (both drainage and tillage). The study was conducted from 2010 to 2014 in a Chinese double-rice field. During winter, total precipitation and mean daily temperature significantly affected CH₄ emission. Compared to NTND, drainage and tillage decreased annual CH₄ emissions in early- and late-rice seasons by 54 and 33 kg CH₄ ha⁻¹ yr⁻¹, respectively. Drainage and tillage increased N₂O emissions in the winter fallow season but reduced it in early- and late-rice seasons, resulting in no annual change in N₂O emission. Global warming potentials of CH₄ and N₂O emissions were decreased by 1.49 and 0.92 t CO₂ eq. ha⁻¹ yr⁻¹, respectively, and were reduced more by combining drainage with tillage, providing a mitigation potential of 1.96 t CO₂ eq. ha⁻¹ yr⁻¹. A low total C content and high C / N ratio in rice residues showed that tillage in the winter fallow season reduced CH₄ and N₂O emissions in both early- and late-rice seasons. Drainage and tillage significantly decreased the abundance of methanogens in paddy soil, and this may explain the decrease of CH₄ emissions. Greenhouse gas intensity was significantly decreased by drainage and tillage separately, and the reduction was greater by combining drainage with tillage, resulting in a reduction of 0.17 t CO₂ eq. t⁻¹. The results indicate that drainage combined with tillage during the winter fallow season is an effective strategy for mitigating greenhouse gas releases from double-rice fields.