Nitrogen Transformations In Broiler Litter As Affected by Relative Humidity.

Broiler litter is a good source of plant available nitrogen (N) for pastures and crops. However, large losses of N to the atmosphere through ammonia volatilization can lead to lower crop yields and environmental contamination. Ammonia volatilization is dependent on many factors: manure management, soil characteristics, and environmental conditions. Environmental conditions may be most influential in ammonia loss from surface application of litter to pastures.  Relative humidity, vapor pressure, and rainfall may play a large role in increased volatilization through the rewetting of litter and increased mineralization of uric acid and urea. Understanding the effect of these environmental factors may help to explain high N loss and lead to more precise rate recommendations. The objective of this study was to determine the effect of environmental conditions on ammonia volatilization from broiler litter.  A field study was conducted in Eatonton, GA from April to September 2011 to determine loss of ammonia from applied litter to a tall fescue pasture.  Litter was applied at a rate of 120 kg total N ha^-1 each month to four circular plots 20 m in diameter.  One rotating mast with passive flux samplers was placed in the center of each treated plot to capture volatilized ammonia.  A rotating mast was also placed upwind of the predominant wind direction to measure background ammonia in the air. Duplicate flux samplers (oxalic acid-coated tubes) were placed at heights of 0.30, 0.75. 1.50, 2.25, and 3 m in each mast and were changed every two weeks.  Tubes were extracted with water and analyzed colorimetrically for ammonium.   A weather station set up in the field provided local environmental conditions  including soil and air temperature, wind speed and direction, rainfall, and relative humidity.  In addition, leaf wetness sensors were used to monitor the presence of water (from dew or rain) on the surface of the pasture.  Typical ammonia losses in a two-week period ranged from 1 to 6 kg N ha^-1 and were related to vapor pressure, rainfall, and presence of water on the surface of the pasture. The rewetting of the litter by rainfall and dew apparently increased microbial and enzymatic activity leading to increases in ammonia loss.