Abstract: A greenhouse experiment was conducted to study the effects of simulated nitrogen deposition on the growth and competition of C₄ weedy species (Echinochloa crusgalli var. mitis L.) and C₃ upland rice (Oryza sativa L.) under day/night temperature of 35 ℃/25 ℃ and 30 ℃/20 ℃. The results showed that under day/night temperature 35 ℃/25 ℃, 4.0 g·m^-2·a^-1 N deposition enhanced the shoot biomass of E. crusgalli and O. sativa by 29.18% and 27.80%, respectively, compared with control. The N and P uptake by E. crusgalli increased by 87.33% and 49.73%, respectively, but no change was found for O. sativa. Under 30 ℃/20 ℃, three N depositions (2, 4 and 6 g·m^-1 ·a^-1) enhanced the shoot biomass, tiller number, and shoot N and P uptake of E. crusgalli by 48.99%, 72.68% and 36.18%, 111.11%, 122.22% and 144.44%, 108.88%, 129.22% and 134.29%, and 16.53%, 65.05% and 22.47%, respectively, but no changes were observed for O. sativa. Nitrogen deposition significantly increased the shoot biomass ratio of E. crusgalli to O. sativa under 30 ℃/20 ℃, but had no impact on this ratio under 35 ℃/25 ℃. It was suggested that N deposition could enhance the competition of E. crusgalli over O. sativa, especially under lower air temperature.

Key words: rice straw biochar, life rubbish biochar, methane, carbon dioxide, nitrous oxide, paddy soil.