Controlled Drainage and Nutrient Management Planning Reduce Drainage Outflow and Nitrogen Transport

Controlled drainage, nutrient management planning, and a combination of both were implemented and evaluated throughout the upper Core Creek watershed to reduce nutrient loading to the Neuse River. Hydrology and drainage water quality were monitored at fifteen locations within the watershed for a period of five years. DRAINMOD-N was calibrated on a field-by-field basis to predict long-term hydrology and nitrate losses based on BMPs implemented and crops grown throughout the watershed. Predicted NO₃-N reduction was most effectively accomplished when controlled drainage and a nitrogen management plan were used in conjunction with one another. If implemented separately, a nitrogen management plan was predicted to be more effective than controlled drainage alone. The cropping system also impacted the drainage rate and nitrate loss from the fields. Potentially, a 30% and 75% nitrate reduction can be achieved growing cotton or soybeans, respectively, as compared to corn. Controlled drainage reduced the drainage outflow by 6.8 centimeters (21.3%) annually, compared to conventional drainage. This flow reduction accounted for 11.5% of the NO₃-N reduction leaving the watershed.