Abstract
This paper provides details of a study to track the lateral seepage of nitrogen through the bunds of a paddy field in Sanjiang Plain, Northeast China. Field simulation experiments were conducted during the rice growing season in 2010 at the experimental plots of the Sanjiang Mire Wetland Experimental Station of the Chinese Academy of Sciences. Measurements revealed that the lateral seepage rates were significantly affected by the irrigation water amount. Once the lateral seepage began, its rate increased with the increasing water level in the paddy field. The concentrations of nitrogen in lateral seepage from the bund showed good responsiveness to the nitrogen application rates and the fertilization time in the paddy field. The nitrogen concentrations increased with increasing urea application rates, and these concentrations decreased sharply within the first few days (10 similar to 15 d) after fertilization, and then presented a stable trend, suggesting that the first few days (10 similar to 15 d) after fertilization were critical period for pollution control. The bund could intercept some of the nitrogen in seepage water, and it presented higher interception ability to total nitrogen (N-t) and ammonium nitrogen (NH4+-N) than that of nitrate nitrogen (NO3--N). For the three urea treatments, the seasonal N-t output loads were estimated to be 7.82, 26.49 and 33.35 kg ha(-1), respectively, taking about 8.69, 14.72 and 12.35 percent of the total nitrogen fertilizer applied. The lateral seepage contributed to more than 35 percent of the nitrogen loss load, and it is one of the most important pathways for nitrogen loss from paddy field.