Ammonia emissions from field-simulated cattle defecation and urination
Received for publication January 11, 2008. Atmospheric ammonia (NH3) is a concern because of its environmental impact. The greatest contribution to atmospheric NH3 comes from agricultural sources. This study quantified NH3 volatilization from cattle defecation and urination on pasture under field conditions in Auburn, Alabama. Treatments consisted of beef feces, dairy feces, dairy urine, and a control. The experiment was conducted during four seasons from June 2003 to April 2004. Fresh feces or urine was applied onto grass swards, and NH3 volatilization was measured up to 14 d after application using an inverted chamber method. Dairy urine was the only significant source of NH3. Ammonia nitrogen (N) loss differed among seasons, ranging from 1.8% in winter to 20.9% during the warmer summer months. Cumulative volatilization was best described in this experiment by the equation % NH3–N loss = Nmax (1 – e–ct)i. The highest rate of NH3 volatilization generally occurred within 24 h. This study suggests that NH3 volatilization from cattle urine on pasture is significant and varies with season, whereas NH3 volatilization from cattle feces is negligible.