Content area
Full Text
Atmospheric ammonia (NH^sub 3^) is a concern because of its environmental impact. The greatest contribution to atmospheric NH^sub 3^ comes from agricultural sources. This study quantified NH^sub 3^ 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 NH^sub 3^ volatilization was measured up to 14 d after application using an inverted chamber method. Dairy urine was the only significant source of NH^sub 3^. 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 % NH^sub 3^-N loss = N^sub max^ (1 - e^sup -ct^)^sup i^. The highest rate of NH^sub 3^ volatilization generally occurred within 24 h. This study suggests that NH^sub 3^ volatilization from cattle urine on pasture is significant and varies with season, whereas NH^sub 3^ volatilization from cattle feces is negligible.
Abbreviations: CP, crude protein; DM, dry matter.
ATMOSPHERIC ammonia contributes to soil and surface water acidification and eutrophication (Hornung and Sutton, 1995; Sheppard, 2002) and to increase the N load on vegetation (Asman, 1998), which may have deleterious effects on environmental quality. Atmospheric ammonia also increases fine aerosol formation in the atmosphere, which reflects incoming solar radiation and thereby contributes to a climatological phenomenon known as radiative forcing (Barthelmie and Pryor, 1998; Adams et al., 2001). Although fossil fuel combustion, sewage treatment operations, and industrial processes contribute to atmospheric NH^sub 3^, these are considered small in comparison to agricultural sources (Buijsman et al., 1987; Whitehead, 1990).
Ammonia fate in soil depends on the competitive processes of nitrification, N fixation, plant uptake, leaching, immobilization, denitrification, and volatilization. Volatilization of NH^sub 3^ is affected by several variables, including temperature (Ball and Ryden, 1984), soil pH, soil cation exchange capacity (Bussink, 1994), wind velocity, soil water content (Ernst and Massey, 1960; Vallis et al., 1982), and rainfall (Doak, 1951).
The major N species in cattle urine is urea, which comprises 50 to 90% of total urinary N (Bussink and Oenema, 1998). Upon contact...