Dairy manure amendment effects on odor and gas emissions

Twenty-two amendments representing different modes of action were screened for odor and gas emission from dairy manure stored at room temperature (20 o C) for short- (3 d) and medium-term (30 d). Seven of these amendments were selected for replicated (n=2-4) study at two temperatures (10 and 20 o C) and three storage periods (3, 30 and 94 d). Amendment was added to 2-kg dairy slurry (1:1.7 urine:feces; 12% total solids) following the manufacturer rates. Untreated slurry was also evaluated as was a feed-through additive. Odor emissions were estimated by six qualified odor assessors following an olfactometry international standard. Odor quality characterizations included hedonic tone, supra-threshold odor intensity, and odor character. Gas emissions measured included hydrogen sulfide (H2S), ammonia (NH3), carbon dioxide (CO2), methane (CH4) and nitrous oxide. There were no consistent reductions of odor and gas emissions in the amendments and feed additive treatments for all storage periods at 20 o C and 10 o C. Average daily odor emission rates were 5 to 94 OUE cm -2 d -1 . Significant reductions (31%; P=0.032) were measured in the abandoned mine drainage (AMD) sediment treatment after 3 d at 20 o C. Essential oils Hyssopus and peppermint reduced odor emission by 27-48% after 94 d at 20 o C. But for 30 d at 10 o C these oil treatments increased odor by 29-65%. Generally, mean gas emission rates were 1.4 to 2 times higher at 20 o C than at 10 o C (P=0.04-<0.0001). Only the AMD sediments consistently reduced NH3 and CO2 emissions after 30 d and 94 d (P=0.02-<0.0001). A microbial digestive treatment (powder enzymes and bacteria) reduced NH3 emissions after 94 d (P=0.006- <0.0001) at 10 o C and 20 o C and CH4 emissions (12%) after 30 d at 10 o C (P=0.005). Storing treated dairy manure for 94 d either at 10 o C or 20 o C reduced odor and greenhouse gas emissions by 88-100%. All treated and untreated manure slurries had unpleasant to extremely unpleasant smell and 76 to 100% of certified odor assessors described manure as offensive, earthy, medicinal and fishy. Odor emission was correlated to odor strength, H2S, CH4 and CO2 emissions but inversely to NH3 emission.