Abstract Recently, vegetated drainage ditches have been used as one of the best management practices for controlling the transport of agricultural pollutants. In this study, a pilot-scale field experiment within a 135-km 2 agricultural catchment was conducted to investigate the effectiveness of ditches vegetated with Pontederia cordata (Pontederia) and Myriophyllum elatinoides (Myriophyllum) and ditches without vegetation (Control) on ammonium (NH 4 + -N) removal and nitrous oxide (N 2 O) emissions. Compared to the control treatment, the ditches with both plant species ( P. cordata and M. elatinoides ) increased NH 4 + -N removal rates by 50.8% and 71.4% and decreased N 2 O emissions by 68.3% and 70.4% for NH 4 + -N loadings of 25 mg L −1 and 70 mg L −1 , respectively. The linear mixed-effect model revealed that effluent NH 4 + -N concentrations were significantly decreased by 2.54% and 2.10% for each increase of one unit on sediment NH 4 + -N sorption and plant TN accumulations ( p 4 + -N removal pathways in Myriophyllum ditch were plant uptake and microbial nitrification-denitrification. However, in Pontederia and control ditches, NH 4 + -N was mainly removed by sediment sorption. These findings may suggest that vegetated drainage ditches (e.g., M. elatinoides ) are capable of removing NH 4 + -N from agricultural runoff and can additionally reduce N 2 O emissions.