FGD-Gypsum's Effect on Ammonia Volatilization from Broiler Litter.

Poultry litter (PL) contains elevated concentrations of organic nitrogen and urea-degrading (ureolytic) microorganisms that facilitate ammonia volatilization.  In order to ensure in-house respiratory safety and the production of a high quality nitrogen fertilizer, ammonia volatilization should be minimal.  Acidifying materials, such as alum, are currently used to limit ureolytic bacteria growth thus suppressing ammonia volatilization.  Limited published data suggest that gypsum may also lower in-house ammonia emissions, but its effect on nitrogen mineralizing microorganisms has not been investigated.  Our objective was to use a series of bench scale studies to determine if amending PL with differential rates of flue gas desulfurization-gypsum (FGD) would significantly reduce microbial presence and activity associated with ammonia volatilization.  Two separate 21-day incubation studies were conducted to determine the effect of 0, 20, and 40% FGD addition on urea-degrading bacteria, nitrogen mineralization, and evolution of CO₂ and NH₃.  The results of experiment 1 indicated that the addition of FGD to PL significantly reduced urea (p < 0.001) and urea-degrading bacteria (p < 0.001), while significantly increasing ammoniacal-N (p < 0.001).  Results of experiment 2 indicated that the addition of FGD to PL did not significantly alter CO₂ evolution, but did significantly reduce NH₃ volatilization (p < 0.001).  NH₃ evolution was not different between PL treated with 20% or 40% FGD (p = 0.259).  Results from these experiments suggest that 20% FGD addition to PL is adequate to reduce NH₃ volatilization in poultry houses compared to untreated  PL.