|AYADI, FEROUZ - South Dakota State University|
|CORTUS, ERIN - South Dakota State University|
Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 4/28/2015
Publication Date: 4/28/2015
Citation: Ayadi, F.Y., Cortus, E.L., Spiehs, M.J., Miller, D.N. 2015. Nitrification and denitrification activity in simulated beef cattle bedded manure packs. In: Proceedings of the 2015 ASABE Intersectional Meeting, North Central Region. St. Joseph, Michigan:ASABE, April 10-11, 2015, Fargo, ND. Paper Number: RRV15-056.
Interpretive Summary: Several beef cattle producers in the Northern Great Plains raise their cattle in deep-bedded confined facilities, such as mono-slope barns. When managing manure, nitrous oxide, a potent greenhouse gas can be released. Denitrification and nitrification are microbially mediated processes leading to nitrous oxide production. We conducted experiments with 36 simulated bedded manure packs (BP) to determine nitrous oxide concentration, and the potential for denitrification and nitrification to occur under different conditions. At the start of the experiment bedded packs were 0, 3 and 6 weeks old (three per treatment) and monitored over three weeks in temperature/humidity-controlled chambers at 10°C (50°F) and 40°C (104°F). The three different age treatments were referred to as 0-3, 3-6 and 6-9 week old BP. Fresh feces from a beef feedlot, urine and two different bedding materials (corn stover and soybean stubble) were added weekly to the packs. Just before weekly addition, samples were hand-grabbed from one, two and three different depths for 0-3, 3-6 and 6-9 week-old packs, respectively, and immediately analyzed to determine nitrification and denitrification potential. Measured denitrification enzyme activity was similar across different zones and up to 1000-fold higher than nitrification activity potential, whereas nitrification activity potential was higher in middle zones. This may be explained by the fact that denitrifying bacteria are ubiquitous and can survive in both the presence and absence of oxygen, whereas nitrifiers are slow-growing microorganisms that require oxygen. Right after material addition, headspaces were sampled for nitrous oxide concentrations at 0, 22, 46 and 142 hours post-addition. In the 40°C environment, nitrous oxide concentrations were highest immediately after material addition and occurred as pulses. These pulses were up to four times higher than concentrations measured at other time points at 10°C and 40°C. The pulse concentrations were likely caused by denitrification activity when fresh bedding, urine, and feces were mixed together. This research showed that nitrous oxide emissions are expected to be higher during the hot summer season (temperatures approaching 40°C) and year round after a bedding event and/or when the barn is scraped. Future research should verify that denitrification is the main process for nitrous oxide emission after the bedded pack is disturbed. It should also be clarified if pulse nitrous oxide concentrations occur after sampling/scraping and/or after a bedding event.
Technical Abstract: Besides significant nitrogen (N) losses through ammonia, N can also be lost as nitrous oxide (N2O) via microbial incomplete nitrification and denitrification in the manure. We conducted lab-scale experiments to determine N2O, denitrification enzyme activity (DEA) and nitrification activity potential (NAP) in simulated beef cattle bedded manure packs (BP) under different conditions. Thirty-six BP were stored in humidity-controlled chambers at 10°C or 40°C, contained either corn stover or soybean stubble as the bedding material, and were 0-3, 3-6 and 6-9 week old. The DEA and NAP were measured weekly before material addition. Samples were taken from varying depths based on BP age, and incubated at room temperature with different reagents and distilled water. For DEA, subsamples were analyzed for both nitrite N and combined nitrite-nitrate N consumption over 56 h of incubation. For NAP, samples were measured for nitrite production over 144 h. Results showed that NAP (1.22 nmol gbedpack-1 h-1, SE = 0.10) was much lower (1000 fold) than DEA (1.93 mmol gbedpack-1 h-1, SE = 0.14). The DEA was similar throughout BP depth, whereas NAP was higher in BP middle section. Nitrifiers are slow growing microorganisms which may explain low NAP in BP, whereas denitrifiers are fast growing communities that can survive in aerobic and anaerobic environments. Surface gas fluxes were measured with static flux chambers (n=2 per treatment). Nitrous oxide concentrations were on average 0.50 ppm (SE = 0.03) with peak concentrations occurring as high pulses right after material addition. Nitrous oxide production was most likely caused by incomplete denitrification from pulse nitrate concentrations available in the dried bedding material. However, future research using specific inhibitors or stable N isotopes should verify which process, nitrification or denitrification, is responsible for N2O production.