On-farm beef cattle methane emissions measured with tracer-ratio and inverse-dispersion modelling techniques

Abstract. The development and validation of management practices to mitigate greenhouse gas (GHG) emissions from livestock requires accurate emission measurements. This study assessed the accuracy of a practical inverse dispersion (IDM) micrometeorological technique to quantify methane (CH4) emitted from a small cattle herd (16 animals) confined to a 63 × 60 m pen. The IDM technique calculates emissions from the increase in CH4 concentration measured downwind of the animals. Two types of open-path (OP) gas sensors were used to measure concentration in the IDM calculation: a Fourier transform infrared spectrometer (IDM-FTIR) or a CH4 Laser (IDM-Laser). The actual cattle emission rate was given by a tracer-ratio technique using nitrous oxide as the tracer gas. We found very good agreement between the two IDM emission estimates (316 and 322 g CH4 head−1 d−1 for the IDM-FTIR and IDM-Laser, respectively) and the tracer-ratio measurements (315 g CH4 head−1 d−1). This study shows that a practical IDM measurement approach can provide an accurate method of estimating cattle emissions.