Effect of minerals on activity of microbial uricase to reduce ammonia volatilization in poultry manure.

Inhibition of microbial uricase in poultry manure is critical to reduce NH3 volatilization, because hydrolysis of uric acid by microbial uricase is the first step in the production of NH3 gas in poultry manure. Three experiments were conducted to evaluate the effects of minerals on uricase activity and NH3 volatilization from poultry manure. In Experiment 1, an in vitro enzyme assay was used to evaluate the effects of Zn, Cu, Mg, and Mn on the activity of microbial uricase. There were three treatments: uricase, uricase + minerals, and uricase preincubated with minerals. Uric acid concentration was measured at 293 nm with a spectrophotometer. The results indicated that Zn and Cu greatly blocked the activity of microbial uricase (>90% inhibition), whereas Mg and Mn were less inhibitory. Experiment 2 was designed to evaluate the effect of ZnSO4 on the growth of uric acid-utilizing microorganisms by an in vitro assay. There were three treatments: control, ZnSO4 (10 mM), and ZnSO4 (50 mM). The results indicated that ZnSO4 significantly reduced the number of uric acid-utilizing microorganisms compared to the control. In Experiment 3, an NH3-trapping system was used to evaluate the effect of different levels of ZnSO4 on NH3 volatilization and nitrogen retention in poultry manure. Poultry manure (300 g) was mixed with 0, 0.15, 0.3, 1.5, 3, or 6 g ZnSO4 to create manure concentrations of Zn at 0, 0.05, 0.1, 0.5, 1, or 2% (wt/wt), respectively. The 1 and 2% ZnSO4 treatments significantly increased manure uric acid and total nitrogen retention by reducing NH3 volatilization compared to the control during the 3-wk incubation.