| Farmland soils have become the largest anthropogenic source of greenhouse gases.It is of great significance for realizing the increase of production and emission reduction of farmland soils to understand the N2O emission characteristics of loess soils under long-term different fertilization in this region.The 28-year long-term fertilization experiment of "National Monitoring Base on Loess Fertility and Fertilizer Efficency " was used that included the long-term non-fertilization(CK),single application of nitrogen fertilizer(N),combined application of nitrogen and potassium(NK),phosphorus and potassium(PK),nitrogen and phosphorus(NP),nitrogen,phosphorus and potassium(NPK),and organic manure and nitrogen,phosphorus and potassium(MNPK)in this study.Soil N2O Emission monitored in situ under the winter wheat-summer fallow rotation system by static dark chamber-gas chromatography.The relationship between soil N2O emission and soil physical and chemical properties was analyzed also to explore the effects of long-term fertilization on greenhouse gas emissions from rainfed dryland farmland,use DNDC to validate soil N2O emission and simulate farmland N2O emission in order to provide a basis for choosing reasonable fertilization methods,improving fertilizer utilization efficiency and reducing soil greenhouse gas emissions,as well as for estimating and compiling a list of greenhouse gas emissions from farmland in China.The results show that:1)The seasonal or annual dynamics of soil N2O fluxes were similar between different fertilization treatments in the two rotation cycles.The peak N2O flux appeared within one week after fertilization,then gradually decreased,and maintained at a low level in winter.Compared with CK,MNPK and balanced fertilization(NPK and NP)significantly increased soil N2O emission flux and emissions.2)The N2O emission factors were showed as NPK > MNPK > NP > NK > N in two cycle years.The average yield-scale N2O emissions was the highest in N fertilizer application in two cycle years,and had no difference between NK and NPK treatment.The average yield-scale N2O emissions were the lowest in PK and NP treatments and there was no significant difference between each other.MNPK and CK treatment had no significant difference with other treatments.3)Long-term combined application of organic and inorganic fertilizers and balanced application of chemical fertilizers can significantly increase the content of soil organic carbon,total nitrogen,nitrate-N,ammonia-N,soil microbial biomass nitrogen(MBN)and microbial biomass carbon(MBC),and reduce soil p H.4)The content of soil nitrate-N,ammonia-N and microbial biomass nitrogen were significantly positively correlated with the N2O emission flux.RDA analysis showed that the importance of soil factors to total N2O emission was as TN > NO3--N > SOC > NH4+-N > MBN > MBC.5)DNDC model could well simulate wheat yield and N2O emissions under different long-term fertilizer treatments.The cumulative N2O emissions estimated by DNDC model were as MNPK > NPK > NP > NK > N > CK > PK in the past 28 years.In conclusion,long-term organic-inorganic combined fertilizer(MNPK)and balanced chemical fertilizer(NP and NPK)significantly improved soil fertility and increased the wheat yields on rainfed farmland.Although cumulative N2O emissions were enhanced,the yield-scale N2O emissions were reduced.That means long-term organic-inorganic combined fertilizer(MNPK)and balanced chemical fertilizer(NP and NPK)still were the good fertilization methods to be recommended on rainfed farmland.If the source and sink analysis of soil carbon can be further combined,it can provide a scientific basis for production improvement and emission reduction for rainfed farmland area. |
PDF Full Text Request