Urea Hydrolysis and Calcium Carbonate Precipitation in Gypsum-Amended Broiler Litter.

Broiler (Gallus gallus domesticus) litter is subject to ammonia (NH₃) volatilization losses. Previous work has shown that the addition of gypsum to broiler litter can increase nitrogen mineralization and decrease NH₃ losses due to a decrease in pH, but the mechanisms responsible for these effects are not well understood. Therefore, three laboratory studies were conducted to evaluate the effect of gypsum addition to broiler litter on (i) urease activity at three water contents, (ii) calcium carbonate precipitation, and (iii) pH. The addition of gypsum to broiler litter increased ammonium concentrations (p < 0.0033) and decreased litter pH by 0.43 to 0.49 pH units after 5 d (p < 0.0001); however, the rate of urea hydrolysis in treated litter only increased on Day 0 for broiler litter with low (0.29 g H₂O g_-1) and high (0.69 g H₂O g_-1) water contents, and on Day 3 for litter with medium (0.40 g H₂O g_-1) water content (p < 0.05). Amending broiler litter with gypsum also caused an immediate decrease in litter pH (0.22 pH units) due to the precipitation of calcium carbonate (CaCO₃) from gypsum-derived calcium and litter bicarbonate. Furthermore, as urea was hydrolyzed, more urea-derived carbon precipitated as CaCO₃ in gypsum-treated litter than in untreated litter (p < 0.001). These results indicate that amending broiler litter with gypsum favors the precipitation of CaCO₃, which buffers against increases in litter pH that are known to facilitate NH3 volatilization. [ABSTRACT FROM AUTHOR]