The effect of an acidified-gypsum mixture on broiler litter urease-producing bacteria and nitrogen mineralization

Ammonia (NH3) volatilization from broiler (Gallus gallus domesticus) litter is a microbially mediated process that can decrease bird productivity and serves as an environmental pollutant. The release of NH3 is strongly influenced by the pH of litter. Flue-gas desulfurization gypsum (FGDG) has been suggested as a potential amendment to reduce NH3 volatilization due to the pH buffering capacity of calcium carbonate (CaCO3) precipitation. However, its effect on litter pH is not as pronounced as acidifying agents, such as aluminum sulfate (alum). The main objective of our study was to develop an acidified-FGDG amendment that has a more pronounced effect on litter pH and NH3 volatilization than FGDG alone. We conducted a 33-d incubation in which litter pH, NH3 volatilization, nitrogen mineralization, PLUP-ureC gene abundance, and CaCO3 precipitation were measured. Treatments in the study included: broiler litter (BL), broiler litter + 20% FGDG (BL+FGDG), broiler litter + FGDG-alum mixture (BL+FGDG+A6), broiler litter + 6% alum (BL+A6), and broiler litter + 10% alum (BL+A10). Our FGDG+alum amendment decreased litter pH (0.68 pH units) and PLUP-ureC gene abundance (>1 log) compared with FGDG alone and the control (p < .05). This led to a 25% decrease in cumulative NH3 loss after 33 d. The addition of FGDG alone did not have an effect on litter pH (p = .36) or cumulative NH3 loss (p = .29) due to a lack of significant CaCO3 precipitation. Treating litter with 6 and 10% alum was the most effective amendment for reducing pH and cumulative NH3 loss.