『Abstract
　The nitrogen (N) budget was developed for Jiulong River Watershed (JRW), an agricultural watershed in a warm and humid area of southeast China. Water quality monitoring, field surveys, modelling and GIS techniques were applied to estimate N flux of atmospheric deposition, mineralization, runoff, denitrification, and ammonia volatilization. Over the whole watershed, fertilizers, import of animal feeds, biotic fixation, mineralization and atmospheric deposition contributed 67.1％, 16.5％, 2.1％, 4.9％ and 9.5％, respectively, of total N input (129.3 kg N ha^-1 year^-1). Runoff, sale of production, denitrification, and ammonia volatilization contributed 7.3％, 24.4％, 10.5％ and 57.8％ of total N output (72.9 kg N ha^-1 year^-1), respectively. The N budget for the JRW suggested that more than 50％ of the N input was lost to the environment, and about 14％ was discharged as riverine N, which indicated that agricultural and human activities in the watershed substantially impacted the estuary and coastal water quality, and so altered the N biogeochemical process.

Keywords: Nitrogen; Sources and exports; Southeast China; Watershed budget

Abbreviation: JRW Jiulong River Watershed』

『要旨
　窒素収支が、中国南東部の温暖湿潤地域の農地流域である九龍川流域に対して展開された。水質モニターリング・野外調査・モデル化・GIS手法が大気沈着・鉱化・流出・脱窒・アンモニア揮発の窒素フラックスを見積るために適用された。全流域に対して、肥料・家畜餌の導入・生物による固定・鉱化・大気沈着は、それぞれ全窒素インプット（129.3キログラム窒素毎ヘクタール毎年）の67.1％・16.5％・2.1％・4.9％・9.5％であった。流出・生産物販売・脱窒・アンモニア揮発は、それぞれ全窒素アウトプット（72.9キログラム窒素毎ヘクタール毎年）の7.3％・24.4％・10.5％・57.8％であった。九龍川流域の窒素収支は、窒素インプットの50％以上が環境に失われ、そして約14％が河川の窒素として流れていることを示し、このことは流域の農業と人間活動が実質的に河口と沿岸の水質に大きな影響を及ぼしており、窒素の地球化学的過程を変化さていることを示す。』

Introduction
Materials and methods
　Study area
　Quantifying N fluxes
　Sources of N input
　　Fertilizers
　　Import of animal feeds
　　Biological fixation
　　Mineralizable N
　　Atmospheric deposition
　Export of N output
　　Sale of crops and animal production
　　Runoff
　　Denitrification
　　Ammonia volatilization
Results and discussion
　Sources of N input
　N outputs
　N budget
　Uncertainty analyses
Conclusions
Acknowledgements
References

Table 1 Coefficients for estimation of nitrogen budget

N sources/exports	Items	N contents	Calculation basis	References
Biotic fixation	Peanuts	86 kg N ha-1 year-1	Land area	Barry et al. (1993)
	Soybean	78 kg N ha-1 year-1	Land area	Barry et al. (1993)
	Paddy	45 kg N ha-1 year-1	Land area	Zhu (1997)
	Other crops	15 kg N ha-1 year-1	Land area	Zhu (1997)
Feeds import	Swine	29 g kg-1	Fresh weight	Personal communication
Products sale	Swine	25 g kg-1	Fresh weight	Fortin and Elliot (1985)
	Banana	2.24 g kg-124	Fresh weight	Chen (2002)
	Citrus	1.28 g kg-1	Fresh weight	Chen (2002)
	Litchi	1.44 g kg-1	Fresh weight	Chen (2002)
	Vegetable	2.88 g kg-1	Fresh weight	Chen (2002)
	Sugarcane	1.0 g kg-1	Fresh weight	Cao and Zhu (2000)
	Rice	31 kg N ha-1 year-1	Land area	Huang et al. (1995)
	Peanut	154 kg N ha-1 year-1	Land area	Huang et al. (1995)
	Bean	89 kg N ha-1 year-1	Land area	Huang et al. (1995)
Denitrification	Banana	17.3 kg N ha-1 year-1	Land area	DNDC Simulated data
	Vegetable	41.0 kg N ha-1 year-1	Land area	DNDC Simulated data
	Fallow	16.1 kg N ha-1 year-1	Land area	DNDC Simulated data
	Paddy	29.3 kg N ha-1 year-1	Land area	Xu et al. (1997); Xing (1998)
	Forest	2.0 kg N ha-1 year-1	Land area	Brumme et al. (1999); Hahn et al. (2000); Henrich and Haselwandter (1997)
	Ponds/water	10 kg N ha-1 year-1	Land area	Sjodin et al. (1997)

Table 2 Nitrogen budget for the Jiulong Rver Watershed

N budget	Ton N year-1	N Flux (kg N ha-1 year-1)	Perrcent of input (％)
Inputs (I)
Fertilizers	127,460	86.7	67.1
Feed	31,296	21.3	16.5
Biological	3,961	2.7	2.1
Mineralizable N	9,230	6.3	4.9
Deposition	18,089	12.3	9.5
Subtotal	190,036	129.3	100
Output (O)
Production sale	7,831	5.3	4.1
Runoff	26,138	17.8	13.8
Denitrification	11,258	7.7	5.9
Ammonia volatilization	61,937	42.1	32.6
Subtotal	107,164	72.9	56.4
Budget (I-O)	82,872	56.4	43.6

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