| An important source of plant nutrient and soil acidification, increased N deposition from the atmosphere will greatly impact production and stability of global terrestrial and aquatic ecosystems. With the spread of air pollution and acid rain from city to suburb and country, special attention is paid to the atmospheric environment in vast rural areas and the effect of atmospheric nitrogen deposition on agricultural ecosystems is increasingly obvious. In this study, the characteristics of atmospheric nitrogen were discussed by rainfall, nitrogen concentration observation and nitrogen deposition velocity of atmospheric nitrogen compounds (Vd) with a big-leaf resistance analogy model and the Auto-Meteorological Experiment Station in a typical red soil agro-ecosystem in Southeastern China for five years (2005-2009). The detailed results were as follows:1. During 2005-2009, the Vd was much higher in the daytime than in the nighttime and had a peak value around noon (11:00-13:00). All of Vd(NH3), Vd(NO2) and Vd(NH4+/NO3-) were higher in winter and spring while Vd(HNO3) in spring and summer. There were also obvious characteristics which Vd(NH3), Vd(NO2) and Vd(NH4+/NO3-) higher during peanut and early-rice growing stage while Vd(HNO3) during early-rice and middle-rice growing stage. The Vd was fluctuations, especially for Vd(NH3) and Vd(NO2) inner one year. The annual Vd were O.25±0.01,0.12±0.01,0.78±0.04 and 0.15±0.01 cm/s for NH3, NO2, gaseous HNO3 and aerosol particles (aerosol NH4+or NO3-), respectively. What's more, both Vd(NH3) and Vd(HNO3) were on the decrease each year. Vd(NO2) remained steady while Vd(NH4+/NO3-) declined in 2005-2007 and then increased in 2007-2009.2. The atmospheric nitrogen concentrations of dry deposition (Ca) were respecially 164.64±93.16, 67.67±44.66,1.9±1.26 and 3.21±2.17?gN/m3 for Ca(NH3), Ca(NO2), Ca(NH4+) and Ca(NO3-) while the atmospheric nitrogen concentrations of wet deposition (Cw) were in the range of 0.05-1.49,0.54-0.72, 0.56-3.71,2.63-5.72 mgN/L for annual means of CW(NH4+-N), Cw(NO3--N), Cw(DON) and CW(TN) in rainwater, respectively. As for gaseous HNO3, its monthly and annual means all went to zero. Seasonally, there had higher vales for Ca(NH3) in spring and winter, for CW(DON) in summer and autumn, and for Ca(NO2), Ca(NH4+), Ca(NO3-), Cw(NH4+-N), Cw(NO3--N) and Cw(TN) in autumn and winter. Both Ca and Cw was higher in non-crop growing stage than that in crop growing stage. During the crop growing stage, there were higher for Ca(NH3) in peanut stage and early-rice stage, and for Ca(NO2), Ca(NH4+), Ca(NO3-) and Cw(NH4+-N) higher in middle-rice stage and late-rice stage, and for Cw(NO3--N), CW(DON) and Cw(TN) higher in early-rice stage and late-rice stage in 2005-2009.3. The nitrogen fluxes of dry deposition (Fd) and wet deposition (Fw) were 73.09±12.87 and 59.18±29.93 kgN/(ha-yr) in 2005-2009, separately. And the ratio of Fw(DIN) and Fw(DIN) was 2.4. In dry deposition, Fd(N, NH3+NO2) was the predominantly Fd, which accounted for 98.09% of Fd. And in wet deposition, Fw(DON) and Fw(DIN) had a similar size. Seasonally, there were higher for Fd in spring and winter, and for Fw in spring and autumn. During the crop growing stage, the Fd and Fw were respectively 34.38±9.87 and 36.57±25.13 kgN/(ha-yr), which highest in peanut stage and lowest in late-rice stage.4. Over the agricultural ecosystem, annual bulk deposition flux of atmospheric nitrogen (Ft) ranged from 94.50-185.99 kgN/(ha-yr), including Ft(DIN) which was 104.20±15.29 kgN/(ha-yr). Ft(DIN) was inputed maily by dry deposition, and Ft(NHx) was the major protein, especially for Ft(NH3). What's more, the Ft had higher value in spring and winter. And the Ft was 70.95±30.88 kgN/ha during the crop growing stage, litter higher than that during non crop growing stage. Inorganic nitrogen was the maily deposition method, which was in the range of 84.24-119.27 kgN/(ha-yr) and averaged 104.20 kgN/(ha-yr). |
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