Nitrogen interception and fate in vegetated ditches using the isotope tracer method: A simulation study in northern China

During periods of heavy precipitation, farmland drainage ditches are the main routes for farmland nitrogen flowing into surface waters in northern China. Vegetated ditches can be engineered to mitigate N loss from agricultural runoff. We used a simulation study to evaluate the interception of nitrogen in a ditch without vegetation and three vegetated ditches. The 15N stable isotope tracer method was used to analyze the fate of ditch intercepting farmland runoff nitrogen. The three vegetated ditches were planted with Lolium perenne L., Bromus inermis Leyss. and Elytrigia repens (L.) Nevski. The results showed that the interception rates of nitrogen in the three vegetated ditches were higher than in the ditch without vegetation. The L. perenne ditch had the lowest interception rates of nitrogen among the three vegetated ditches. The interception of nitrogen by the three vegetated ditches was primarily achieved by the capture of nitrogen runoff in the soil ditch bed, which allowed water infiltration. Nitrogen retained in the ditch bed soil of the ditch without vegetation was enriched in the 0–10 cm soil layer from surface mainly. However, in the three vegetated ditches, it was transported to the 50 cm soil layer. All of the nitrogen retained in the vegetated ditches was absorbed by the L. Perenne and E. repens, and the interception of nitrogen was affected by plant species and growth stage in the vegetated ditch.