杭州稻麦菜轮作地区大气氮湿沉降

Atmospheric N wet deposition in Hangzhou region under rice-wheat-vegetable cropping system

通过雨水中NH4+-N/NO3--N比率和铵态氮自然丰度值(δ15NH4+)的变化探讨大气氮湿沉降与农作施肥活动的关联性。2003年6月至2005年7月,采用自行设计定制的雨水收集器在浙江杭州稻-麦-蔬菜轮作地区进行了为期2a的全天候连续雨水采样分析。结果显示,杭州稻-麦-蔬菜轮作地区雨水中NH4+-N/NO3--N比率和δ15NH4+值呈现相似的季节性变化,雨水中NH4+-N/NO3--N的峰值出现在6月底～9月上旬,而后逐渐下降,秋冬季(10～11月份)降到最低;来春麦菜集中施肥期(2～3月份),又呈现多个小高峰;5～6月份为单季稻和蔬菜基肥和追肥集中施用期,故而峰值也达4以上;入冬后仅在麦田施肥期出现一个小高峰而后明显下降,大都降到1以下;频繁施肥期雨水中的NH4+-N/NO3--N比率值是农闲期的2～4倍,显示雨水NH4+-N/NO3--N比率与农田施肥活动有密切关联与同步性,但与气温无直接关联(R2=0.0129)。雨水中δ15NH4+值的变化,与雨水中NH4+-N/NO3--N比率相似,呈现明显的季节性变化:稻麦生育后期与种前空闲期为正值,麦稻蔬菜集中施肥期转为负值。雨水中NH4+-N/NO3--N比率与δ15NH4+值对大气湿沉降中氮的来源、形态及地面NH3排放源的强度有一定的表征意义。

The ratio of NH4^＋ -N/NO; -N and natural ^15N abundance of NH4^＋ （ δ^15 NH4^＋） in rainfall in Hangzhou of Zhejiang province, China was determined between June 2003 and July 2005 using customized manual rainwater sampler. Our measurements indicated a similar seasonal variation in the NH4^＋ -N/NO3^--N ratio and δ^15NH4^＋ value in rainfall; peaks of NH4^＋ -N/NO3^- -N ratio in rainfall occurred when the farmland received fertilizers, followed by gradual decline to a lower level when the crop was harvested or the fertilizer application was terminated. In contrary, the δ^15NH4^＋ value stayed negative when Nsubstances were applied to the crop, and then turned to positive when the crop was harvested or field was in fallow. Both NH4^＋-N/NO3^--N ratio and δ^15 NH4^＋ value in rain precipitation were evidently correlated with the chemical nitrogen fertilizer application during various crop growth stages, the alternation of seasonal transitions, and NH3 volatilization from other NH3 emission sources. Therefore, they could be regarded as an indicator in determining the sources, forms and composition of N in atmospheric wet deposition as well as the intensity of various NH3 emission sources from the land.