Evaluating a lagoon effluent land application system and the effect of controlled drainage and vegetative buffer strips on drainage water quality

Most of the animal waste from hog production in eastern North Carolina is temporarily stored in anaerobic lagoons before being applied to agricultural land as organic fertilizer. Two immediate concerns of such a system are lagoon safety and nutrient loss from the application fields. The objectives of this study were (1) to assess the lagoon performance in a land application system using DRAINMOD, and (2) evaluate the effect of two Best Management Practices, controlled drainage (CD) and vegetative buffer strips (VBSs), on drainage water quality.;Lagoon safety and performance was evaluated by conducting long term simulations using DRAINMOD. Crop nitrogen budget, lagoon mass balance, and lagoon emergency operation routines were added to the original model. While the current emergency design standards are based on the 24-hour, 25-year storm, the most hazardous period for lagoon operation was during wet winter months. In summer months, a lagoon usually had the storage space for severe storms because of high evaporation and frequent waste application. In order to avoid lagoon overflow nitrogen application had to sometimes exceed the requirement of cover crops. Field drainage conditions and cropping systems also affected lagoon performance.;A field experiment was conducted to monitor drainage water quality from waste application fields in eastern North Carolina. Controlled drainage and VBSs were implemented. Occasional high concentrations of nitrogen in drainage water (>100 mg/L, mostly still in the form of Total Kjeldahl Nitrogen (TKN)) were caused by applying waste on wet soils. Lower drainage outflow from controlled drainage treatments was observed, as well as reduction of Total-P on the treatments with VBSs. However, the treatment effects were generally overshadowed by short duration high concentration periods.;Nitrogen and phosphorus loss could be high in the short period after waste applications. Using a 20 day screening window, we found that up to 90% of the annual loss occurred after six application events. Runoff volume and water table depth at the time of application were found to be important factors affecting the loss. Based on the relationship between the nutrient loss and hydrologic factors derived from the field measurements, long-term simulations showed that nutrient loss could be reduced by requiring deeper water table depth prior waste application. However, this also reduced the total amount of wastewater that could be applied and treated due to narrowed operation windows on poorly drained soils.