Abstract: The Chenwu Town Reservoir Watershed of Jurong, Jiangsu Province, is a typical rice-based agricultural watershed in the Yangtze River Delta region of China. Based on the data collected from stationary observation and field investigation of the rice-based agricultural watershed from May 2007 to April 2008, nitrogen flow was balanced for the analyses and prediction of pollution potential of the farmland nitrogen to the watershed. Results show that the total input of nitrogen was 1 589.1 t, while the total output of nitrogen was 1 168.4 t in the watershed during the period. Fertilizer application was the dominant source of nitrogen input, accounting for 67.2% , and harvest of crops was the majorway of nitrogen output, accounting for 46.7%。Balancing of input with output showed N surplus in both paddy fields and up land fields, of 20.5% and 52.4% , respectively, demonstrating low nitrogen use efficiency, being 33.6% and 34.9% , respectively. In paddy fields, about 47.8% of the N input was lost in gaseous form. The gaseous nitrogen and the remaining nitrogen in soil are ready pollutants to the air and waterbodies.

Key words: agricultural watershed, nitrogen balance, paddy field, non-point source pollution, Yangtze River Delta region