Effect of controlled drainage on nitrogen fate and transport for a subsurface drained grass field receiving liquid swine lagoon effluent

•Controlled drainage reduced drainage flow by an average of 93%.•Controlled drainage reduced total nitrogen loading by an average of 94%.•67% of nitrogen reduction via drain outlet was due to enhanced denitrification.•The nitrogen reduction efficiency reduced to 66% if considering lateral seepage.•Controlled drainage raised daily water table depth significantly by 15 cm.