Measuring methane emissions from two dairy farms: Seasonal and manure-management effects

There is a need to improve the understanding of methane (CH4) emissions on multiple spatial and temporal scales, and on a sector basis. Livestock are significant contributors to the CH4 budget, with emissions coming from enteric fermentation by ruminants and management of liquid manure. Inventory estimates for methane emissions are based on methodology that needs to be verified with actual on-farm measurements. Responding to these needs, the objectives of this study were to apply the backward Lagrangian Stochastic (bLS) technique on small dairy farms (50-100 lactating cows) and to examine its suitability to determine CH4 emissions from whole farms and partition emissions from cattle and manure. Measurement campaigns were selected to characterize the emission response to farm management activities and seasonal changes. At both farms the whole-farm emission rate was measured when the liquid manure storages were either full or emptied. Emissions from manure were substantial, and in the fall when the manure storage was full, 60% of the whole farm emissions came from the manure storage. Substantial seasonal differences in whole-farm emissions were observed, with fall season emissions being ∼40% higher than in the spring due to much higher manure emissions in the fall (673 g lactating-cow−1 d−1) than the spring (249 g lactating-cow−1 d−1). Peak emissions from stored manure were 47 kg CH4 h−1, (730 g lactating-cow−1 h−1) during agitation. The enteric emission rate from the animals (after subtracting estimated barn floor emissions) showed clear diurnal variation and on a daily basis was similar for both seasons, ranging between 270 and 380 g lactating cow−1 d−1. Implied Ym values were lower than the IPCC default value. Methane emissions from manure exhibited pronounced temporal variation on multiple time-frames and as a result, more research is needed to fully describe annual CH4 emissions from liquid manure management.