Analysis of temporal and spatial variation of nitrogen in fieldditch system of small agricultural watershed
ZHANG Zhan-Yu, CHEN Jing-Jing, ZHANG Wen-Xiang, SI Han
(1.Key Laboratory of Efficient IrrigationDrainage and Agricultural SoilWater Environment in Southern China, Ministry of Education, Nanjing, Jiangsu 210098, China; 2.College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing, Jiangsu 210098, China)
A typical agricultural small watershed in summer season in Lishui county, Nanjing city was specified as a study model to explore the temporal and spatial variation trend of nitrogen in the small watershed. The temporal and spatial variation of soil nitrogen in the watershed was investigated by insitu observation, indoor laboratory analysis and statistics regression, eventually the distribution characteristics of nitrogen concentration in the drainage ditch were clarified. It was turned out that the profiles of three forms of soil nitrogen content against time show some differences, namely, the total soil total nitrogen content gets the maximum at a time instance, but both the soil nitrate nitrogen and ammonium nitrogen are subject to a steady decrease and the maximum declines are 37.1% and 60.9%. In the central area of the watershed the soil total nitrogen content is the highest, meanwhile the total nitrogen in the southern area is higher than that in the northern part. The averaged concentrations of the total nitrogen, nitrate nitrogen and ammonium nitrogen are 3.54, 0.81,0.59 mg/L in the drainage ditch during summer. In water migration process in the ditch, the concentrations of three forms of nitrogen at the outlet of the ditch are always higher that those at the entrance.
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