A new tracer experiment to estimate the methane emissions from a dairy cow shed using sulfur hexafluoride (SF 6 )

Methane emission from livestock and agricultural wastes contribute globally more than 30% to the anthropogenic atmospheric methane source. Estimates of this number have been derived from respiration chamber experiments. We determined methane emission rates from 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 , CO 2 , and SF 6 , a trace gas which has been released at a constant rate into the stable air, have been measured. The ratio between SF 6 release rate and measured SF 6 concentration was then used to estimate the ventilation rate of the stable air during the course of the experiment. The respective ratio between CH 4 or CO 2 and SF 6 concentration together with the known SF 6 release rate allows us to calculate the CH 4 (and CO 2 ) emissions in the stable. From our experiment we derive a total daily mean CH 4 emission of 441 L STP per cow (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 CH 4 release from about 50 m 3 of liquid manure present in the cow shed in underground channels. Also, considering measurements we made directly on a liquid manure tank, we obtained an estimate of the total CH 4 production from manure: The normalized contribution of methane from manure amounts to 12–30% of the direct methane release of a dairy cow during rumination. The total CH 4 release per dairy cow, including manure, is 521–530 L STP CH 4 per day.