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The Core Creek Project implemented and evaluated best management practices (BMPs) throughout the upper watershed to reduce nutrient loading to the Neuse River. A portion of the Core Creek Project evaluated the reduction of nitrate (NO3-N) leaving the Core Creek watershed due to the implementation of controlled drainage and nutrient management plans. DRAINMOD-N was calibrated and extrapolated 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.