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JEH Volume 10 (2002), Paper 7, October 2002
Posted October 25, 2002
NITROGEN CYCLING AND REMOVAL EFFICIENCY IN A RICE FIELD
A.H. Gallardo
Program in Life and Environmental Sciences, University of Tsukuba,
Ibaraki, Japan
N. Tase
Institute of Geosciences, University of Tsukuba, Ibaraki, Japan
ABSTRACT
The major sources and sinks of nitrogen (N) were calculated during
the rice growth cycle in a lowland paddy field in Japan in order to better
understand contamination of surface and groundwater. Deposited nitrogen
totalized 106 kg ha -1 , entering the field primarily through
fertilizers and irrigation waters. Nitrogen outputs represented 93 kg ha
-1 , most of it removed when crops were harvested. Excess nitrogen
(13 kg ha -1 ) was assumed to be stored in soils. The distribution
of nitrogen concentrations clearly correlated with agricultural land use
patterns. The nitrogen cycle was affected by the unique characteristics
of submerged soils and involved complex transformations, mostly governed
by the activity of microorganisms. Although there were some considerable
losses as infiltration and surface runoff, the mass balance calculations
showed that the paddy field was a nutrient sink within the region. Nitrogen
assimilation capacity was higher than similar systems, and remained invariable
during all the recorded period. The results demonstrate the importance
of using a mass balance approach to evaluate the effects of agricultural
production on water quality, and to assess how to reduce negative impacts
through improved management strategies.
Reference: Gallardo, A.H., and N. Tase; Nitrogen Cycling
and Removal Efficiency in a Rice Field, Journal of Environmental Hydrology,
Vol. 10, Paper 7, October 2002.
CONTACT:
Adrian Gallardo
University of Tsukuba, Institute of Geosciences
Ibaraki-ken, Tsukuba-shi
Tennodai 1-1-1
Japan 305-8571
E-mail: adgallardo@yahoo.co.jp