Herbicide management of roadside kudzu (Pueraria lobata) vegetation doubles soil nitrification and nitrate leaching rates

Kudzu (Pueraria lobata), a fast-growing leguminous vine with broad global distribution, is one of the main species occurring in roadside vegetation, particularly in Asia and the United States. Kudzu has been reported to have negative effects on ecosystem functions by increasing nitrification and nitric oxide emissions. Because of these negative effects and its extensive growth, roadside kudzu vegetation is often targeted for herbicide management, despite its contribution to erosion control. The effects of kudzu removal on soil nitrogen (N) dynamics and N leaching from roadside vegetation remain unclear. In this study, we established experimental plots alongside a highway in central Japan and used herbicide to manage the roadside kudzu vegetation. We then measured the effects on soil N dynamics and N leaching from the ecosystem during the growing season using a polyvinyl chloride core to exclude N uptake by plant roots. Our experiment showed that kudzu management with herbicide strongly affected soil N dynamics by altering soil temperature and moisture through the removal of kudzu coverage. The net nitrification rate in the herbicide-treated plots was higher than that in the control plots; therefore, nitrate–N leaching increased. In contrast, herbicide management did not significantly affect net ammonium–N production or leaching. The results demonstrate that kudzu removal results in a spike of belowground nitrate leaching.