关键词: Granier经验公式, 毛白杨, 热扩散式探针, 树干液流

Abstract: Paddy field is an important N₂O emission source. Nitrogen fertilization is one of the main influencing factors for N₂O emissions from paddy field. Therefore, it is significant to clarify reasonable nitrogen fertilization to maintain high rice yield and reduce N₂O emissions. With the conventional fertilization as control (CF, 150 kg N·hm^-2 in the early and late season rice, respectively), three nitrogen application rates (nitrogen fertilizer reduction 30%, 23%, and 16%, respectively) were set up with deep placement to examine the effects of reduction and deep placement of nitrogen fertilizer on rice yield and N₂O emissions from double cropping paddy field. The results of a two-year field experiment showed that, through applying chemical fertilizers at a depth of 7 cm in soil,  nitrogen fertilizer reduction 30% significantly increased the numbers of productive ear and grains and increased grain yield by 5%. Reduction and deep placement of nitrogen fertilizer obviously reduced N₂O emissions from double cropping paddy field. Compared with CF treatment, nitrogen fertilizer reduction 30% significantly diminished the accumulative emission of N₂O by 57% and 72% in the early and late growing season, respectively. In addition, reduction and deep placement of nitrogen fertilizer changed the N₂O emission pattern. The N₂O emission peak appeared at the tillering stage in the CF treatment, while there was only low N₂O emission at the seeding establishment and ripening stages in the treatments with reduction and deep placement of nitrogen fertilizer. In conclusion, rational nitrogen fertilizer reduction combined with deep placement can maintain grain yield and mitigate N₂O emissions from double cropping paddy field.

Key words: Populus tomentosa, Granier empirical formula, sap flow, thermal dissipation probe (TDP)