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Emissions of ammonia, nitrous oxide, methane, and carbon dioxide during storage of dairy cow manure as affected by dietary forage-to-concentrate ratio and crust formation

Aguerre, M. J., Wattiaux, M. A., Powell, J. M.
Journal of dairy science 2012 v.95 pp. 7409
air flow, ammonia, ammonium nitrogen, barns, barrels, carbon dioxide, carbon nitrogen ratio, dairy cows, dairy manure, feed concentrates, forage, gas emissions, greenhouse gases, litter (bedding), methane, methane production, nitrous oxide, pH, storage time, straw, total mixed rations
Sixteen 200-L barrels were used to determine the effects of dietary forage to concentrate ratio (F:C) on rates of NH3-N, N2O, CH4 and CO2 emission from dairy manure during a 77-d storage period. Manure was obtained from a companion study where cows were assigned to total mixed rations that included the following F:C ratio: 47:53, 54:46, 61:39 and 68:32 (diet dry matter (DM) basis) and housed in air-flow controlled chambers constructed in a modified tie-stall barn. On day 0 of this study, deposited manure and bedding from each emission chamber was thoroughly mixed, diluted with water (1.9 to 1 manure to water ratio) and loaded in barrels. In addition, on days 0, 7, 14, 28, 35, 49, 56, 63, 70 and 77 of storage, rate of NH3-N, N2O, CH4 and CO2 emission from each barrel were measured. Data were analyzed as a randomized complete block with four replications. Dietary F:C ratio had no effect on manure DM, total N and total ammonia N (NH3-N + NH4+-N), and pH at the time of storage (mean ± SD 10.6±0.6%, 3.0±0.2%, 93.1± 18.1 mg/dL, and 7.8±0.5, respectively). No treatment differences were observed in overall rate of manure NH3-N, N2O, CH4 and CO2 emission (mean ± SD over the 77-d storage period; 117±25, 30±7, 299±62, and 15,396±753 mg/hr per m2, respectively). The presence of straw bedding in manure promoted the formation of a surface crust that became air-dried after about one month of storage and was associated with an altered pattern in NH3-N and N2O emissions in particular. Whereas NH3-N emission rate was highest on d 0 and gradually declined until reaching negligible levels on d 35, N2O emission rate was almost nil the first two weeks of storage, increased sharply to peak on d 35 and declined subsequently. Emission rate of CH4 and CO2 peaked simultaneously on d 7, but declined subsequently with a distinct pattern. In this study, C:N ratio of gaseous losses was 32:1 reflecting higher volatile C loss than volatile N loss during storage. Furthermore, the most important source of non-CO2 greenhouse gas emitted was CH4 until formation of an air-dried crust, but NO2 thereafter. Taken together, these results suggest that the formation of an air-dried crust resulting from the straw bedding present in the manure reduced drastically NH3-N and CH4 emission, but was conducive of N2O production and emission.