Impact Of Nitrogen Management On Alfalfa Yield, N₂O And CH₄Emissions

Recently, atmospheric CH4and N2O are continuously increasing from800ppb to1800ppb and from270ug/L to319μg/L, respectively. It has been indicated that the agricultural sources are one of the major emission sources. Therefore, it is a hot-spot to explore the impact of nitrogen management on greenhouse gases emissions from various agricultural sources. In this study, the impacts of N management on the yield of alfalfa, N use efficiency as well as the CH4and N2O emissions were investigated using plot experiment. Field measurements were started at June of2012, five treatments including control (CK), chemical N fertilization (CF), chemical N plus cattle manure (DM1), chemical N plus digestate (DT) as well chemical N plus reduced cattle manure (DM2). The main results are in below:(1) N fertilization not only enhanced the yields and N accumulation of alfalfa, also might have a potential of reducing the period among two cuttings and increase the total cuttings during a year.(2) It was found that the N use efficiency of chemical N fertilizer was46.7%～48.1%during the experimental periods,9.1%for cattle manure and13.8%for digestate, indicating the N use efficiency of organic fertilizer was lower than chemical N fertilizer.(3) Application of chemical N fertilizer or organic manure or digestate can both increase the alfalfa yields. In addition, applying extra cattle manure on the basis of chemical N fertilization can further increase yield, but it cannot replace the chemical N fertilization due to its low N use efficiency.(4) Analysis on seasonal and annual emissions showed that N2O emission in summer was significantly higher than winter season, indicating that the soil temperature, moisture and soil nitrogen affected N2O emissions from upland; Meanwhile, annual variation of N2O emissions were mainly determined by the difference of N2O emissions in summer seasons. During the first cutting period after fertilization, soil N2O flux without fertilization treatment was significantly lower than the fluxes of all fertilization treatments, but no significant difference among these fertilization treatments were found. During the measurement period, DT was with the highest N2O emission, which was137.74%,43.38%,22.44%and29.47%greater than CK, CF, DM1, DM2, respectively.(5) During the measurement period, alfalfa fields were a sink of atmospheric methane. Compared with the CK treatment, fertilization treatment inhibited the absorption of methane, although the difference was not significant. In addition, no correlations between methane uptake and the amount of fertilizers were observed.