TREATMENT OF SILAGE RUNOFF USING VEGETATED FILTER STRIPS

Vegetative filter strips have the potential to treat agricultural runoff and reduce the pollutant load that reaches surface waters. Filter strips are used to infiltrate and remove nutrients from high-volume, low-concentration silage runoff produced from precipitation events. Following infiltration events, nitrates can form from organic nitrogen and ammonia, enter the subsurface drainage, and potentially contaminate groundwater. This study quantifies the surface and subsurface concentrations and nutrient load reductions provided by filter strips with different design storms. Two 3.7 m x 1.2 m filter strips were constructed, and silage runoff was applied at rates simulating a 25-year 24-hour design storm and a 2-year 24-hour design storm for a bunker pad to filter strip area ratio of 1:1. The filter strips had a >80% reduction of SRP and TP in the subsurface drainage when compared to the silage runoff influent. Subsurface drainage reduced total ammoniacal nitrogen, BOD5, and COD by 29% to 77%, 37% to 76%, and 40% to 76%, respectively. The pH of the subsurface drainage was increased from 4 to greater than 6.