Ammonia Emission during Irrigation of Dairy Manure.

Application of liquid manure through irrigation systems has become more common in recent years. Emission of NH₃ from surface-applied manure has been well documented, but less is known about emission during the irrigation process itself. We carried out a series of 11 experiments over a two-year period to assess NH₃ loss, five with center pivot (CP), four with traveling gun (TG), and two with tanker spreaders. Liquid dairy manure (after solids separation) averaged 1.4 % solids and 81 g/kg total N and 54 g/kg NH₄-N on a dry matter basis. Ammonia emission during each irrigation event (45 min to 1.5 h) was assessed using two approaches. 1) Pairs of passive ammonia samplers (Ogawa and Co., USA, Inc.) 15 m apart were placed at different distances downwind from the irrigated manure (15, 30, 60, 107, 152, and 213 m) at a 1.7 m height; two samplers were placed upwind at 30 and 60 m distances. 2) Three pairs of collection pans (20 x 30 cm) were placed on the soil surface ahead of the irrigation pass and were collected immediately after they were passed by the traveling gun or pivot sprinklers. Ammonium-N concentrations in pan samples were compared to those taken from the irrigation line. Concentrations of NH₃-N from the passive samplers varied among the center pivot runs, but four of five showed a logarithmic decrease with distance, suggesting that NH₃ was being volatilized during manure irrigation. Concentrations from the traveling gun were lower and showed less consistent patterns with distance. There were significant decreases in the NH₄-N and/or NH₄-N/total P and/or NH₄-N/DM ratio of the manure collected in pans compared to that from the irrigation line in two of the CP and three of the TG runs (ranging from 7 to 35% in those with significant decreases). These results suggest that NH₃ emission occurs during irrigation of manure under some conditions, and is significantly correlated with wind speed.