| The area covered by vegetables has been increased rapidly in recent years.With the characteristics of the high level of water and nitrogen(N)fertilizer inputs,vegetable productional ways suffers from low nitrogen use efficiency(NUE)and a high gaseous nitrogen loss,and vegetable field has become an important source of the agricultural greenhouse gas emissions(GHGs).Nitrous oxide(N2O)and nitric oxide(NO)are important active gaseous N forms,which are the main components of greenhouse effect,ozone layer destruction and atmospheric chemical reaction.Vegetable ecosystem has high N2O and NO emissions,which mainly affected by large application of N fertilizer.The combined application of organic manure and inorganic urea N fertilizer has been considered as an effective way to reduce N loss and improve soil quality.Thus,the invenstgation of the influences of different combinations of organic manure and inorganic urea N fertilizer on N2O and NO emissions and global warming potential(GWP)induced by N2O and CH4 will provide scientific guidance for reducing the environmental pollution of gaseous N and GHGs emissions in vegetable production.A field experiment was established in a typical intensive vegetable field in Southeastern China with four treatments:CK(without N application),M1N1(organic manure M and inorganic urea N fertilizer at the ratio of 1:1),M2N1(organic manure M and inorganic urea N fertilizer at the ratio of 2:1)and NPK(urea),and the N amount was equally applied in the N-fertilized treatments.Four vegetable crops,namely,Baby bok choy,Coriander herb,Spinacia oleracea and Ipomoea aquatica forsk were successfully planted from Sep 2015 to Sep 2016.A one-year field experiment was conducted to investigate the dynamic of N2O,NO and CH4 emissions as affected by different treatments.Meanwhile,the dynamic of the soil inorganic N,WFPS and other environmental parameters including vegetable yield and N uptake of vegetable crops were monitored as well.The objective of this field study was to explore the effects of different combinations of organic manure and inorganic urea N fertilizer on N2O and NO emissions,vegetable yield,NUE,GWP and greenhouse gas intensity(GHGI).The main results were listed as follows:1.During the four vegetable crops growing period,N2O emission was significantly higher than NO emissions in the vegetable ecosystem.The NO/N2O ratio was significantly different in different treatments.Patterns of N2O and NO emissions showed the same trend in the experimental period,which mainly emitted from April to October,and significant emission peaks were observed after fertilization and irrigation events.However,the NO emission peak appeared 3-5 days later than the N2O emission peak.During the entire observation period,significant positive correlations between soil temperature at the 10 cm depth and N2O emission fluxes were observed,and whereas no significant correlation between NO emission fluxes and soil temperature was detected.The WFPS ranged from 39%to 59%,which was positively correlated with N2O emissionsand negatively correlated with NO emission fluxes during the experimental period.In NPK,the N2O flux had significant positive correlation with soil inorganic nitrogen content(NH4++NO3+),and the NO flux had significant positive correlation with soil ammonium N content(NH4+).However,the N2O fluxes had no significant correlations with soil nitrate,ammonium and inorganic N contentsin the other treatments.The N2O cumulative emissions were significantly different among different treatments,and N fertilizer significantly increased soil N2O emissions.The N2O cumulative emissions of CK,MINI,M2N1 and NPK were 7.81 ± 1.51,14.85±2.29,19.33±2.96 and 22.99±3.12 kg N ha-1,respectively.The effects of different combinations of organic manure and inorganic urea N fertilizer on N2O emission were different in each vegetable crop.Compared to NPK,the N2O cumulative emission of MINI was significantly reduced in Baby bok choy,Coriander herb and Ipomoea aquatica forsk seasons,and whereas it had no significant effect on N2O emission in Spinach season.Similar to N2O emission,CK had the lowest cumulative NO emissions of 0.98 kg N ha-1,NPK had the highest NO cumulative emissions of 4.14 kg N ha-1,and cumulative NO emissions of MINI and M2N1 were 3.27 and 2.48 kg N ha’1 respectively.Compared with CK treatment,N application significantly increased the NO fluxes by 2.5-4.2 times(P<0.05).However,there were no significant differences in cumulative NO emissions among the N-fertilized treatments.Besides,the NO/N2O ratio of MINI was the highest by 0.22,CK was the lowest by 0.13,M2N1 and NPK were 0.14 and 0.18 respectively,which indicated the significantly difference of the NO/N2O ratio among different treatments.2.Fertilization significantly increased vegetable yields.No significant difference in the annual vegetable yields and NUE was detected between the N-fertilized treatments,during the whole observation period.Vegetable yields of CK,MINI,M2N1 and NPK were 99.4,196.1,187.4 and 190.2 t ha-1,respectively.Compared with CK,NPK,MINI and M2N1 significantly increased the annual vegetable yields by 91.3%,97.2%and 88.5%,respectively.However,compared with M2N1 and NPK,MINI significantly increased the yield by 21.4%and 33.6%,respectively,in Ipomoea aquatica forsk season.Additionally,inspinach season,NPK significantly increased the yield of spinach by 136.7%and 144.4%,respectively,compared with MINI and M2N1.The NUE of MINI and NPK was significantly greater than M2N1,and there was no significant difference between MINI and NPK,during the whole observation period.There were no significant difference in NUE between nitrogen treatments in Baby bok choy and Coriander herbseasons.However,in Spinach season,the NUE of NPK was 2.18 and 2.37 times of MINI and M2N1.In the Ipomoea aquatica forsk season,the NUE of MINI and M2N1 were 1.66 and 1.29 times of NPK,respectively.3.The combined application of organic manure and inorganic urea N fertilizer significantly affected the GWP induced by CH4 and N2O emissions from vegetable field.The GWP from CK,MINI,M2N1 and NPK were 7.81 ± 1.51,14.85±2.29,19.33±2.96 and 22.99±3.12 t CO2 eq ha-1,respectively.N2O emissions dominated the GWP,which accounted for 83.1%of the GWP in this study.The cumulative CH4 emissions from CK,MINI,M2N1 and NPK were 8.09±14.36,12.43±12.89,9.17±13.33 and 11.70±18.89 kg C ha-1,respectively,and there was no significant difference on CH4 emissions between different treatments,which indicated that the combined application of organic manure and inorganic urea N fertilizer had no significant effect on the CH4 emissions.Compared to NPK,M2N1 had no significant effect on the GWP,while the GWP of MINI was significantly reduced by 33.2%.Thus,different ratios of organic manure and inorganic urea N fertilizer had different effects on the GWP.4.The combined application of organic manure and inorganic urea N fertilizer significantly affected the GHGI.No significant difference in the total vegetable yield was observed in N-fertilized treatments.Compared with NPK,the GWP of MINI was significantly reduced,and thus the GHGI of M1N1 was significantly decreased.M2N1 had no significant effect on the GWP,so there was no significant difference in GHGI,compared with NPK.The MIN1 treatment(organic manure M and inorganic urea fertilizer N at the ratio of 1:1)was recommended in this study to ensure vegetable yields and decrease N2O emissions and GWP stimultaneously in the process of vegetable production. |
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