Galloway,J.N.(1998): The global nitrogen cycle: changes and consequences. Environmental Pollution, 102, 15-24.

『世界的な窒素循環:変化と結果』


Abstract
 In the absence of human activities, biological N fixation is the primary source of reactive N, providing about 90-130 Tg N year-1 (Tg = 1012 g) on the continents. human activities have resulted in the fixation of an additional 〜150 Tg N year-1 by energy production, fertilizer production, and cultivation of crops (e.g., legumes, rice). Some sinks of anthropogenic N have been estimated (e.g., N2O accumulation in the atmosphere; loss to coastal oceans), however due to the uncertainty around the magnitude of other sinks (e.g., retention in groundwater, soils, or vegetation or denitrification to N2) a possibly large portion of the N fixed by humans is missing. While we know that N is accumulating in the environment, we do not know the rate of accumulation. Due to the myriad of effects of excess N on humans, ecosystems, and the atmosphere, and their cascading nature (i.r., one atom of N can have a large number of different effects as it is transformed to different N species), this lack of knowledge is unfortunate. There are limited options available to society to reduce the amount of N mobilized by human action because there is, in effect, a N imperative - it is required for food production. As population and per capita consumption of food (especially animal products) increase, more and more N will be converted from unreactive to reactive forms in the future. This is especially true in less developed regions.

Keywords: Nitrogen; fertilizer; Asia; global change; food production』

Introduction
Nitrogen cycle
 Pre-human world
 Current world
Population and resources
The role of nitrogen
 Temporal patterns in N mobilization
 N distribution and fate
The consequences of nitrogen
The future: the nitrogen imperative
Conclusions
Acknowledgements
References


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