Figure 11. Average annual total nitrogen transport (TKN and No3-N) in drainage outflow as measured at the field edge of 14 sites in eastern North Carolina. Note that nitrogen transport is greater in subsurface flow than in surface runoff, and is four to five times higher in agricultural drainage than in forestland drainage.
Bar Graph of conventional drainage and controlled drainage vs. total nitrogen

Controlled drainage results in a net 45 percent reduction of nitrogen.