PSI-1 - A minimum amount of hydrochloric acid for pig urine collection to inhibit nitrogen volatilization

The objectives were to demonstrate that nitrogen volatilization from pig urine can be inhibited by the addition of acids and to determine a minimum amount of HCl for nitrogen preservation in pig urine. In experiment 1, five urine samples were collected and had nitrogen concentrations of 0.29% to 0.68%. Each sample was divided into 2 groups that were supplemented with 100 mL of distilled water and 100 mL of 6 N HCl, respectively. The samples were placed in open containers at room temperature for 10 d. The nitrogen concentration was determined every 2 d. The amount of nitrogen in urine supplemented with distilled water decreased linearly (P < 0.001) with time, whereas that supplemented with 6 N HCl remained constant. In experiment 2, three urine samples with different nitrogen concentration (0.12%, 0.53%, and 0.94%) were added with different amounts of 6 N HCl used to make varying acidity (pH = 0.6, 1.1, 2.2, 4.7, 7.1, and 9.3). All urine samples were placed at a room temperature for 5 d followed by nitrogen analysis. Based on a linear broken-line analysis, nitrogen was not volatilized at a pH less than 5.12 (SE = 0.71), whereas nitrogen was volatilized at a pH greater than 5.12 (r² = 0.98). An equation was developed for the minimum amount of 6 N HCl in urine to avoid nitrogen volatilization: 6 N HCl in urine (g/L) = 0.11 × nitrogen in urine (g/L) + 0.2 with r² = 0.93 and P < 0.01. Assuming that up to 200 gram of nitrogen is excreted for 5 d, the addition of 100 mL of 6 N HCl to the urine collection container can inhibit nitrogen volatilization. Taken together, a minimum of 100 mL of 6 N HCl is recommended for 5 day-total collection of pig urine.