title: Recent trends of nitrogen flow of typical agro-ecosystems in China--major problems and potential solutions.
abstract: BACKGROUND
  To diagnose problems that threaten regional sustainability and to devise appropriate treatment measures in China's agro-ecosystems, a study was carried out to quantify the nitrogen (N) flow in China's typical agro-ecosystems and develop potential solutions to the increasing environmental N load.
  
  
  RESULTS
  The analysis showed that owing to human activity in the agro-ecosystems of Changjiang River Basin the mean total input of anthropogenic reactive N (i.e. chemical fertiliser, atmospheric deposition and bio-N fixation) increased from 4.41 × 10(9) kg-N in 1980 to 7.61 × 10(9) kg-N in 1990 and then to 1.43 × 10(10) kg-N in 2000, with chemical fertiliser N being the largest contributor to N load. Field investigation further showed that changes in human behaviour and rural urbanisation have caused rural communities to become more dependent on chemical fertilisers. In rural regions, around 4.17 kg-N of per capita annual potential N load as excrement was returned to farmlands and 1.38 kg-N directly discharged into river systems, while in urbanised regions, around 1.00 kg-N of per capita annual potential N load as excrement was returned to farmlands and 5.62 kg-N discharged into river systems in urban areas.
  
  
  CONCLUSIONS
  The findings of the study suggest that human activities have significantly altered the N cycle in agro-ecosystems of China. With high population density and scarce per capita water resources, non-point source pollution from agro-ecosystems continues to put pressure on aquatic ecosystems. Increasing the rate of organic matter recycling and fertiliser efficiency with limited reliance on chemical fertilisers might yield tremendous environmental benefits.
authors: Graduate School of Environmental Studies, Nagoya University, Chikusa-ku, Nagoya, Japan. liu.chen@b.mbox.nagoya-u.ac.jp
authors: Chen
authors: C
authors: Liu
authors: Qinxue
authors: Q
authors: Wang
authors: Yonghui
authors: Y
authors: Yang
authors: Kelin
authors: K
authors: Wang
authors: Zhu
authors: Z
authors: Ouyang
authors: Yan
authors: Y
authors: Li
authors: Alin
authors: A
authors: Lei
authors: Tetsuzo
authors: T
authors: Yasunari
mesh_terms: D000383:Agriculture / Q000379:methods*; D001272:Atmosphere; D001519:Behavior; D002681:China; D003247:Conservation of Natural Resources; D017753:Ecosystem; D005243:Feces; D005308:Fertilizers; D006801:Humans; D009584:Nitrogen / Q000032:analysis* / Q000378:metabolism; D058458:Nitrogen Cycle; D009586:Nitrogen Fixation; D011156:Population Density; D045483:Rivers; D014507:Urbanization; D014876:Water Pollution
chemical_list: D005308:Fertilizers; D009584:Nitrogen