『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