A new tracer experiment to estimate the methane emissions from a dairy cow shed using sulfur hexafluoride (SF6)

Methane emission f rom l ivestock and agricultural wastes contribute globally more than 3 0 % to the anthropogenic atmospheric methane source. Estimates of this number have been derived f rom respiration chamber experiments. W e determined methane emission rates f rom a tracer experiment in a modern cow shed hosting 43 dairy cows in their accustomed environment. During a 24-hour period the concentrations of CH 4 , C 0 2 , and SF6 , a trace gas which has been released at a constant rate into the stable air, have been measured. The ratio between SF6 release rate and measured SF6 concentration was then used to estimate the ventilation rate of the stable air during the course of the experiment. The respective ratio between C H 4 or C 0 2 and SF6 concentration together with the known SF6 release rate allows us to calculate the C H 4 (and C 0 2 ) emissions in the stable. From our experiment w e derive a total daily mean C H 4 emission of 441 LSTp per c o w (9 cows nonlactating), which is about 15% higher than previous estimates for German cows with comparable milk production obtained during respiration chamber experiments. The higher emission in our stable experiment is attributed to the contribution of C H 4 release f rom about 50 m 3 of l iquid manure present in the cow shed in underground channels. Also , considering measurements we made directly on a l iquid manure tank, w e obtained an estimate of the total C H 4 production f rom manure: The normalized contribution of methane f rom manure amounts to 12-30% of the direct methane release of a dairy c o w during rumination. The total C H 4 release per dairy cow, including manure, is 521-530 LSTp C H 4 per day.