Nitrogen Originating From Environment In Paddy Ecosystem Under Anthropogenic Influences

Atmospheric nitrogen (N) deposition was continually monitored year-roundly at three sites (Nanjing, Changshu and Hangzhou) in the Yangtze River Delta region. The amount of N from atmospheric dry and wet deposition was estimated as well. In the present study, we investigated N pollutant in water bodies of main twelve rivers and three lakes in Changshu region. A simulated experiment of repacked soil columns in flooding field condition enable us to explore the N pollutant sources in surface water of Taihu region and to estimate the amount of N input from river water irrigation into paddy field. The amount of reactive N released from farmland (including N loss of leaching, runoff and ammonia volatilization) into environment was also monitored. Undisturbed tension-free monolith lysimeters (1m² with lm height) were installed during the rice and wheat seasons in this experiment. Moreover, in combination with the ¹⁵N-tracing method, N exchanges among fertilizer, soil, air and plant were also investigated through field and sand culture experiments in two seasons of rice and wheat. The following are main results from the experiments:(1) The amount of N from wet deposition through rainfall was 22.7 kg N ha^-1 yr^-1, 24.5 kg N ha^-1 yr^-1and 30.0 kg N ha^-1 yr^-1 in Nanjing, Changshu and Hangzhou, respectively, with an average wet N deposition of 25.7 kg N ha^-1 yr^-1. The 2 mol L^-1 KC1 extractable N from atmospheric particles reached about 7.16 kg N ha^-1 yr^-1, which is considered contributable to agricultural production. The results also showed that there was obviously seasonal difference in atmospheric N deposition: the wet N deposition in rice season was higher than that of wheat season, while the seasonal changes in dry N deposition was opposite to that of the wet deposition.(2) Based on the NH₄⁺/NO₃^- ratios and δ¹⁵NH₄⁺ values in rainwater at three sites in the Yangtze River Delta, NH₄⁺ sources in atmospheric wet deposition were also discussed. Regular changes in the NH₄⁺/NO₃^- ratios in rainwater were observed at all the three monitoring sites. These changes were mostly caused by seasonal changes in NH₄⁺ concentrations in rainfall and were closely related to the N application time,...