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

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 modem cow shed hosting 43 dairy cows in their accustomed environment, During a 24-hour period the concentrations of CH4, CO2, 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 CH4 or CO2 and SF6 concentration together with the known SF6 release rate allows us to calculate the CH4 (and CO2) emissions in the stable, From our experiment we derive a total daily mean CH4 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 CH4 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 CH4 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 CH4 release per dairy cow, including manure, is 521-530 L(STP) CH4 per day.