Nitrate loss via overland flow and interflow from a sloped farmland in the hilly area of purple soil,China

Nitrate losses through runoff (both overland flow and interflow) represent a significant portion of the nitrogen (N) biogeochemical cycle. The mechanisms of this cycle have been well documented for flat agricultural lands. It is unclear, however, how nitrate loss takes place in sloping farmlands of purple soil. This paper reports the finding of a field experiment examining nitrate losses due to overland flow and interflow along sloping farmland sites dominated by a regosol known as purple soil in the Sichuan Basin, Southwest China. During rainfall events, the nitrate contents in the overland flow initially increased and then decreased gradually, however, the nitrate contents in the interflow increased and then approached to a steady status. The average nitrate concentrations in the overland flow and the interflow were 0.7 ± 0.2 and 21.7 ± 2.1 mg N L⁻¹, respectively. The annual nitrate loss loads through the overland flow and the interflow were 0.9 ± 0.1 and 33.5 ± 2.7 kg N ha⁻¹, respectively accounting for 0.6 and 22% of the fertilizer applied in the growing season. Nitrate was predominantly lost via interflow in the sloping farmland in Sichuan Basin, Southwest China. The experimental farmland was located in the upper stream of the Yangtze River, and the conclusions yielded from this study can be applied to interpreting the eutrophication and groundwater pollution patterns that are currently occurring in this watershed.