Abstract: Through pot experiments, this paper studied the effect of urease inhibitor hydroquinone (HQ), nitrification inhibitor dicyandiamide (DCD) and their combination (HQ+DCD) on the N₂O and CH₄ emissions from a lowland rice soil. The results show that with no wheat straw powder amended, all treatments with inhibitors significantly reduced the N₂O and CH₄ emissions during rice growth, as compared with the treatment only urea applied. Especially for treatment HQ+DCD, its total amount of N₂Oand of CH₄ emission was about 1/3 and 1/2 of the control, respectively; while with wheat straw powder amended, the total N₂O emission of this treatment was 1/2 of the control, but that of CH₄ emission had less difference. Wheat straw powder amendment induced one times and more emissions of N₂O and CH₄ than no its application, and hence, even only from the standpoint of diminishing soil source greenhouse gases emission, applying unmatured composted organic materials with urea is an inappropriate fertilization system. The N₂O flux from this soil had a significant positive exponential relationship with the NO₃^--N content of rice plant and a significant positive linear relationship with the mineral Ncontent in soil surface waterlayer, while CH₄ flux had a significant negative linear relationship both with the growth rate of rice plant and with the mineral Ncontent in soil surface waterlayer. There existed a quantitative trade off between N₂O and CH₄ emission in case of no wheat straw powder incorporated, while with its amendment, the trade off still existed, but hard to quantify.

Key words: Hydroquinone, Dicyandiamide, N₂O, CH₄, Lowland rice field ecosystem, CH₄, global warming potential, rice-wheat rotation system, greenhouse gas intensity, N₂O, aged-biochar