Microbially induced calcium carbonate precipitation in broiler litter and its effect on soil pH

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 CaCO₃ by ~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. macroides and found to precipitate significantly more CaCO₃ than 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.