Where does the rest of the nitrate go?
Nitrate reductions from drainage management systems result from three factors: (1) reduced volume of drainage water exported from the system, (2) denitrification within the soil profile, and (3) deep seepage. The decrease in drainage water has been measured in several locations and is a major factor in reducing nitrate flow to ditches and streams. Some of the water that is not drained becomes surface runoff instead, but nitrate concentrations are considerably lower in the surface runoff. Denitrification converts some of the nitrate to harmless nitrogen gas (N2) as well as a small amount of nitrous oxide (N2O), a potent greenhouse gas, but the extent of denitrification is not known. The amount of deep seepage has not been quantified, nor has the extent to which the nitrate will be denitrified as it travels through these pathways.
