The Effect of Dew on Ammonia Volatilization from Surface-Applied Broiler Litter.

Previous studies have indicated that atmospheric water can lead to increased ammonia (NH₃) volatilization from surface-applied broiler litter.  While observing the effects of environmental variables on NH₃ volatilization from surface-applied poultry manure, we measured an increase in litter water potential from -20 MPa to -11.5 MPa from 12 pm to 6 am the following morning.  This change in water potential is equivalent to an increase from 30 to 50% in litter water content from atmospheric deposition of water and/or dew.  Increased litter water content can lead to increased mineralization of organic nitrogen and increased loss through NH₃ volatilization, leading to an overall decrease in the fertilizer value of poultry manure. To further study this effect, a 15 d NH₃ volatilization study was conducted using a dynamic flow through system with diurnal temperature and relative humidity fluctuations with and without dew.  Broiler litter was surface applied to dry soil (0.03 g g^-1) and received simulated dew treatments of 0.4 g H₂O, equivalent to 0.2 mm of dew every 24 h.  Treatments that received dew had significantly greater NH₃ loss than those that did not (11 % versus 8% of the applied total N).  These findings suggest that dew may play an important role in NH₃ volatilization from surface-applied manure and should be included in modeling NH₃ loss.