『Abstract
The present study evaluated nitrogen (N) input and output in
mainland China using updated data of temporally and spatially-based
land use maps and statistical data at national and provincial
scales. The total n inputs increased from 3,081 kg km-2
in 1985 to 5,426 kg km-2 in 2007. Chemical fertilizer
dominated the N input and showed an increasing trend. Biological
n fixation was the second important N input till 1990 and atmospheric
deposition became the second most important source after that,
accounting for 24.0% in 2007. There was no net n input through
food/feed import in 1985, but it accounted for 3.5% of the total
n input in 2007. According to a mass balance model, we assumed
total N input equal to output. The results showed that more than
half of the total N was denitrified or stored in the system. Ammonia
volatilization accounted for 18.9-22.9% of the total N input,
and N export to water bodies accounted for 17.9-20.7%. About 5.1-7.7%
of the N input was emitted to the atmosphere through biomass burning.
When calculated per unit area, total N input, n export to water
bodies, denitrification and storage could be very well explained
by human population density. Nitrogen input and major outputs
were also positively related to per capita gross domestic product
and the percentage of total land area used as cropland. The N
budget is compared to that of some other countries and the environmental
impacts of the N cycle is discussed.
Keywords: Nitrogen deposition; Chemical n fertilizer; Ammonia
volatilization; Denitrification』
Introduction
Data and methods
N budget model
Basic data
N inputs
Biological fixation
Chemical fertilizer
Atmospheric wet and dry deposition
Net food and feed import
N outputs
NH3 volatilization
Reactive N export to water bodies
Biomass burning emissions
Denitrification and storage
Uncertainty analyses of N budgets
Results
Sources of N input
N output and storages
Discussion
Factors influencing N budget
Comparison with N budget in other countries
Riverine N export of the three major rivers
Environmental consequences of the N budget
Uncertainties in N budget
Acknowledgments
References