『Abstract
　The transfer of nutrients from agricultural land to waters attracts the attention of policy makers as well as scientists as it plays an increasingly significant role in affecting the water environment. It is therefore essential to first understand the nutrient flow in agricultural systems and then correspondingly formulate a series of cost-effective policies and best management practices (BMPs). On the basis of an emission inventory analysis (EIA) and a nutrient full balance (NFB) calculation, this paper presents a partial substance flow analysis (SFA) method, as well as an Agricultural Phosphorus Flow Analysis (AgiPhosFA) model, to describe the phosphorus (P) flow in the agricultural systems in China and assess the impact of human activities on waters driven by agriculture and rural life. It is estimated that average P input and output were 28.9 kg ha^-1 a^-1 and 14.2 kg ha^-1 a^-1 respectively in China in 2004, while the total P utilization efficiency (Plant uptake P/P input) in agriculture was 45.7％ leading to an average P surplus of 14.7 kg ha^-1 a^-1. Excessive P application through mineral fertilizer in the arable farming system has led to the accumulation of soil P and constituted a risk to the recipient water quality, whereas the grassland grazing system is confronted with a severe P deficit problem which has resulted in widespread grass degradation. Therefore it may be an efficient way to mitigate the problems simultaneously by regulating and balancing the P flows between the two systems. Uncertainties of the method and model are also discussed in terms of model conceptualization, data and parameters, and spatial and temporal variability.

Keywords: agricultural pollution; Emission inventory; Nutrient balance; Phosphorus; Substance flow analysis; Uncertainty』

1. Introduction
　1.1. Driving forces of agricultural pollution in China
　1.2. The biogeochemistry of phosphorus
　1.3. Aims of the study
2. The methodology and data
　2.1. The model of agricultural phosphorus flow analysis (AgiPhosFA)
　2.2. Statistical data and coefficients
3. Results and discussion
　3.1. Full phosphorus balance in Chinese agriculture in 2004
　3.2. Phosphorus flow in Chinese agriculture in 2004
　3.3. P release from soil into water in Chinese agriculture in 2004
　3.4. Uncertainties in the methodology and the model
　　3.4.1. Conceptualization of the system
　　3.4.2. Data and parameters
　　3.4.3. Spatial and temporal variability
4. Conclusion and further work
Acknowledgements
References

Fig. 1 . The biogeochemistry of phosphorus. Source: adapted from Smil (2000), Hassan et al. (2005), Liu and Ayres (2006), and Liu et al. (2008). 〔Chen,M., Chen,J. and Sun,F.(2008)によるAgricultural phosphorus flow and its environmental impacts in Chinaから〕

Fig. 3 . P flow in China agriculture. 〔Chen,M., Chen,J. and Sun,F.(2008)によるAgricultural phosphorus flow and its environmental impacts in Chinaから〕

Fig. 10 . Area-specific P load to aquatic environment by country. Source: EEA (2005), *presents area-specific P load in arable land in China. 〔Chen,M., Chen,J. and Sun,F.(2008)によるAgricultural phosphorus flow and its environmental impacts in Chinaから〕