Interception effects of an ecological ditch,used to control agricultural non-point source pollution in subtropical China,on nitrogen transport in surface runoff were studied by monthly measuring the runoff volume and concentrations of ammonium nitrogen( NH~+_4-N),nitrate nitrogen( NO~-_3-N) and total nitrogen( TN) at the ditch inlet and outlet from 2013 to 2014. In addition,differences of NH~+_4-N,NO~-_3-N and TN removal were compared between 2013 and 2014. The results showed that the study ecological ditch...