Relative Humidity and Dew Effect On Ammonia Volatilization From Broiler Litter.

Broiler litter is a good source of plant available nitogen (N), but  N losses through ammonia volatilization can reduce its N availability. Relative humidity (RH) and dew deposition may play a large role in increased volatilization through  rewetting of litter and increased mineralization of organic N. Understanding the effects of relative humidity and dew deposition may help to better estimate ammonia losses. The objectives of this study were to determine the effects of   i) RH on litter drying or rewetting, ii) daily dew deposition on litter water potential (WP), and iii) RH and dew on ammonia volatilization.  Dry or wet litter was placed in RH-controlled jars (90% or 40% RH) and changes in water potential were monitored over several days.  Litter rewetted slowly under 90% RH, changing from -20.2 MPa to -4.04MPa in 120 hours.  However, after 46 hours under 40% RH, litter dried from -4.3 MPa to -102.5 MPa..  To determine the effect of dew on litter WP, samples at -20 MPa were placed outside in shallow plastic cups late evening.  The same samples were then retrieved after dewfall (6 am) and WP was measured.  Water potential increased by 10 MPa, indicating  a large wetting potential from typical dewfall. Three laboratory studies were conducted to determine the effects of RH and dew on ammonia volatilization.  Studies 1 and 2 were held at constant RH, ~90% and 60%, respectively, at 25° C with two soil moisture content sub-treatments (4% and 16%).  Study 3 mimicked typical weather patterns of fall in Georgia with diurnal changes in temperature (6 to 27°C) and RH (40% to 90%), and included simulated, daily dew treatments (~0.2 mm). In all three studies, broiler litter was added at 200 kg N ha^-1.  Ammonia traps were collected and soil/litter analyzed for inorganic N and water content.