Effects of nitrocompounds on uric acid-utilizing microorganisms, nitrogen retention, and microbial community in laying hen manure
A study was conducted to evaluate effects of nitrocompounds on growth of uric acid-utilizing microorganisms, nitrogen retention, and microbial community in laying hen manure. There were three treatments: control, 100 mM nitropropanol (NPL), and 100 mM nitropropionic acid (NPC). The mixed laying hen manure was divided into 3 groups and incubated at 23°C for 7 days. On Days 0, 3, and 7, samples were collected to measure the quantity of uric acid-utilizing microorganisms, total nitrogen retention, and microbial community changes. Both nitrocompounds significantly reduced growth of the uric acid-utilizing microorganisms on Day 3 (P < 0.05). Inhibitory effects of both nitrocompounds remained until Day 7 when the experiment was terminated. NPL treatment retained significantly more manure nitrogen compared to the control on both Days 3 and 7. Manure nitrogen levels of NPC treatment were also significantly higher than the control on Day 7. We further investigated the effects of NPL and NPC on microbial community changes during a 7-day incubation. NPC treatment and control on Day 7 exhibited 94% community similarity. NPC on Day 3 and NPL on Day 7 also showed high community similarity (approximately 94%). Control on Day 0 and Day 7 yielded less than 80% community similarity. Control and NPL treatment groups on Day 3 gave the lowest community similarity (approximately 64%) compared to the other groups. This result indicated that incubation time and treatment moderately influenced microbial community changes. In summary, these results indicate that both nitrocompounds increased manure nitrogen retention by inhibiting the growth of uric acid-utilizing microorganisms, and that NPL and NPC could be used as manure treatments in order to reduce ammonia volatilization and nitrogen retention in poultry manure. Moreover, nitrocompounds may have potential as feed additives to reduce ammonia volatilization.