ObjectiveNitrogen and phosphorus pollution is commonly observed in the rivers of a city in southern China during rainy seasons. It is found that the main sources of pollution in this river are the rainfall runoff from surrounding roads and vegetable farmland alongshore the river. To further determine the contribution rate of farmland rainfall runoff to the pollution of the river, this study monitors and analyzs the output patterns and characteristics of pollutants of rainfall runoff from typical vegetable farmland alongshore the river.MethodsIn this study, a typical vegetable farmland along a river in a southern city was selected as the research object, and rainfall runoff was monitored from June 2022 to August 2022, including water level and flow velocity, and sampling points were set up to collect rainwater runoff, and the pH value of the water samples was adjusted to below 2 by adding acid to the site, and the suspended solids (SS), total phosphorus (TP), phosphate ($P{O}_4^{3-}$), total nitrogen (TN), ammonia nitrogen and other indices of the water samples were subsequently detected and analyzed.ResultsIt was showed that TP was the main pollutant in farmland rainfall runoff, with the average and maximum mass concentrations of 6.91 mg/L and 13.32 mg/L, respectively. Dissolved inorganic phosphorus was the main form of phosphorus discharge, accounting for 74% of TP on average. When rainfall scoured farmland, the initial scouring intensity of each pollutant was ranked as ammonia nitrogen> TP > SS > TN > dissolved organic matter (DOM), and the initial scouring effect was more likely to occur when continuous rainfall scoured farmland.ConclusionThrough the study of this region, it is found that dissolved inorganic nitrogen and inorganic phosphorus in rainfall runoff are the main forms of nitrogen and phosphorus in runoff, and the main task of controlling agricultural non-point source pollution in this region is to reduce phosphorus emissions.