Micrometeorological techniques for measurement of enteric greenhouse gas emissions

Measurement of greenhouse gas (GHG) emissions is a challenge to the animal industry as it is difficult to accurately measure enteric emissions from ruminants. Enclosed chambers and tracer-ratio techniques are common measurement approaches, but their use can alter animal diet, behavior and stress levels and soil emission processes. Non-interfering techniques which do not impact soil or air transport processes, or the animal or its surroundings, provide a more appropriate approach to determine absolute emissions. While micrometeorological integrated horizontal flux and mass difference techniques have been used to study animal emissions in paddocks, they require substantial instrumentation and are practical only for small paddocks. Classical micrometeorological methods such as flux-gradient, eddy covariance, relaxed eddy accumulation and boundary layer budgeting have been used to evaluate emissions from larger source areas. This review focuses on a new technique, inverse dispersion analysis, which is a more flexible approach to measure emissions from small paddocks or whole farms as it allows fluxes to be calculated from gas concentration measurements of interest at a point upwind and a point downwind, along with statistical information on wind turbulence measured using a three dimensional sonic anemometer. Our purpose is to discuss advantages and disadvantages of these various techniques to determine absolute amounts of enteric emissions from ruminants, and provide examples of their application. This article is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors; K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson.