This paper aimed to explore the comprehensive effects of biochar, dicyandiamide (DCD) and their combined application on the greenhouse gas (N₂O, CO₂ and CH₄) emissions from facility soil, so as to provide a scientific basis for reducing the greenhouse gas emissions and green development of facility vegetable production system.

In this study, the facility vegetable production system was used as the research object, and a total of six treatments were set up, including no nitrogen application (CK), traditional nitrogen application (CN), recommended nitrogen application (RN), recommended nitrogen application+biochar(RNB), recommended nitrogen application + DCD (RND), and recommended nitrogen application+biochar+ DCD(RNBD). A pot experiment method was applied to analyze the effects of soil greenhouse gas emissions, and the difference in greenhouse gas intensity (GHGI) and global warming potential (GWP) under different treatments.

Compared with the CN treatment, the rape yield decreased by 2.9%-29.3% under the recommend nitrogen treatments (RN, RN, RND and RNBD). However, under the same nitrogen application rate, the rape yield increased by 34.4% in the treatment of recommend nitrogen combined with biochar and DCD (RNBD), indicating that biochar and DCD showed a synergistic effect on rape yield increase (P<0.05). The recommend nitrogen treatments reduced the soil N₂O emissions by 29.4%-76.5% in comparation with the CN treatment, especially the RND treatment showed the best effect. However, the recommend nitrogen treatments showed little effect on soil CO₂ and CH₄ emissions. Compared with the CN treatment, the total GWP under the recommended nitrogen treatments decreased by 4.3%-51.2%, and the RND treatment showed the best emission-reduction effect. In terms of GHGI, the difference among the recommended nitrogen treatments was not significant (P>0.05), and the RND treatment also showed the best emission-reduction effect.

Under the same nitrogen application rate, the application of biochar alone or DCD alone had little effect on rape yield, but the combination of biochar and DCD could significantly increase the rape yield. Additionally, the combination of biochar and DCD could reduce the cumulative greenhouse gas emissions and GWP, but it was not superior to single application of DCD in the facility vegetable field.