Journal of Environmental Hydrology

ISSN 1058-3912

Electronic journal of the International Association for Environmental Hydrology 

On the World Wide Web at 
JEH Volume 10 (2002), Paper 7, October 2002                   Posted October 25, 2002 

A.H. Gallardo
Program in Life and Environmental Sciences, University of Tsukuba, Ibaraki, Japan
N. Tase
Institute of Geosciences, University of Tsukuba, Ibaraki, Japan

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. 

Adrian Gallardo
University of Tsukuba, Institute of Geosciences
Ibaraki-ken, Tsukuba-shi
Tennodai 1-1-1
Japan 305-8571


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