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Ureolytic microbes are abundant in broiler litter (BL), and previous research indicates that microbially induced calcium carbonate precipitation via urea hydrolysis occurs in gypsum‐amended litters. Given that calcium carbonate (CaCO3) is used to correct soil acidity, we hypothesized that the soil‐liming potential of BL + gypsum is greater than that of unamended litter. First, an experiment was conducted to isolate ureolytic bacteria from BL and confirm their ability to precipitate CaCO3. To determine the effects of calcium on urea hydrolysis, six isolates were identified from screenings of 30 colonies collected from different BL sources. Calcium increased the ureolytic rate by 29%–160% and the precipitation of CaCO3by ~1500% in solution. The 16S rRNA of the isolate with the greatest rate of urea hydrolysis was sequenced and belong to Lysinibacillus macroides. Broiler litter amended with gypsum was inoculated with L. macroidesand found to precipitate significantly more CaCO3than inoculated litter without gypsum. Finally, over the course of a 28‐day incubation, the pH and inorganic‐N of soil, soil + BL, and soil + BL + gypsum were measured. Surprisingly, soil + BL + gypsum was found to have a significantly lower pH than soil + BL for the first 21 days. We propose that the decreased liming ability of BL + gypsum is due to a combination of pH buffering mechanisms and increased nitrification. Although gypsum is a useful litter amendment, it cannot be used to increase the liming ability of litter, despite the fact that gypsum‐amended litter has more CaCO3. Calcium ions increase the rate of urea hydrolysis by poultry litter‐derived ureolytic isolates.Inoculating gypsum‐amended litter with ureolytic bacteria increases the CaCO3and NH4+content of litter.The soil liming potential of gypsum‐amended litter is not greater than the liming potential of unamended litter, even though treated litter contains more CaCO3.

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 NH3is strongly influenced by the pH of litter. Flue‐gas desulfurization gypsum (FGDG) has been suggested as a potential amendment to reduce NH3volatilization 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 NH3volatilization than FGDG alone. We conducted a 33‐d incubation in which litter pH, NH3volatilization, nitrogen mineralization, PLUP‐ureCgene abundance, and CaCO3precipitation 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‐ureCgene abundance (>1 log) compared with FGDG alone and the control (p< .05). This led to a 25% decrease in cumulative NH3loss after 33 d. The addition of FGDG alone did not have an effect on litter pH (p= .36) or cumulative NH3loss (p= .29) due to a lack of significant CaCO3precipitation. Treating litter with 6 and 10% alum was the most effective amendment for reducing pH and cumulative NH3loss. Acidified gypsum decreases ammonia volatilization from broiler litter.FGD gypsum and acidified gypsum reduce urease‐producing bacteria in broiler litter.Calcium carbonate does not form in gypsum amended litter with a pH <8.Litter pH has a strong effect on ammonia volatilization.