Manure Application Method and Timing Effects On Emission of Ammonia and Nitrous Oxide.

Manure is a valuable source of N for crop production, but gaseous losses of manure N as ammonia (NH₃) and nitrous oxide (N₂O) reduce N available to the crop, adversely affect air quality, and contribute to increased greenhouse gas emission. We conducted a field study on corn to evaluate the effect of liquid dairy manure applied pre-plant (injection or 1-h or 3-day disk incorporation) or sidedressed at 5-leaf stage (injected or surface-applied) on emission of NH₃ and N₂O. Manure was applied at a rate of 60 m³ ha^-1, which supplied an average of 170 kg ha^-1 of total N and 70 kg ha^-1 of NH₄-N. Ammonia emission was measured for 3 d after manure application using the dynamic chamber/equilibrium concentration technique, and N₂O flux was quantified using the static chamber method at intervals of 3 to 14 d throughout the season. Ammonia losses were 20 to 50 kg N ha^-1 from pre-plant surface application (30 to 60 % of applied NH₄-N), most of the loss occurring in the first 12 h after application. Emission rates were reduced by as much as 75% by 1-h disk incorporation and over 90% by injection. Losses of N₂O were relatively low, but pronounced peaks of N₂O flux occurred from either pre-plant or sidedress injected manure in different years. Results show that NH₃ emission from manure can be reduced substantially by injection or quick incorporation, but there may be some tradeoff with N₂O flux from injection.