The potential for plants to trap emissions from farms with laying hens. 1. Ammonia

The potential of vegetation to trap NH₃ discharged from a layer house through the exhaust fans was evaluated at The Pennsylvania State University Poultry Education and Research Center in September 2005. Five tree species were planted in pot-in-pot containers in 5 rows downwind of the house fans and in 2 control rows upwind of the hen house. Each row included 1 plant (upwind) or 2 plants (downwind) per species per row. When measured with a photoacoustic NH₃ detector at the same elevation as the fan (1.5 m), NH₃ concentration decreased sharply with greater distance, from 51.54 ppm at 0 m (at the fan) to 1.89 ppm at 5.5 m (between row 2 and 3), 0.27 ppm at 10 m (after row 5), and 0 ppm at 50 m (control). This trend was also observed with the dosi-tubes and photoacoustic detector at the 0.3- and 3.0-m elevations. Significantly lower NH₃ concentrations were recorded when the trees were present downwind of the fans compared with when the trees were removed (16.45 vs. 19.35 ppm), suggesting a portion of the atmospheric NH₃ was being held by the plants. This was further supported by a marked decrease in foliar N status of the plants with greater distance from the source. Plant species also differed, with willow appearing to be the most responsive species and effective as an NH₃ trap.