A new Tier 3 method to calculate methane emission inventory for ruminants

Abstract Livestock is the main source of methane (CH 4 ) emissions. It is important to accurately determine emissions from ruminants that meet standardized international guidelines for national greenhouse gas inventories. A new method to improve the accuracy of CH 4 emissions that complies with IPCC rules for a Tier 3 method is described and evaluated. This method, developed by INRA (French Institute for Agricultural Research), was applied to the French inventory of CH 4 emissions by ruminants and compared with the IPCC Tier 2 method. For enteric CH 4 , depending on the animal category, the INRA CH 4 emission estimates lay between 88% and 114% of IPCC's. The INRA/IPCC ratio for enteric emission was close to unity and did not differ between methods ( P  = 0.43) for adult cows (i.e. most cattle). In France, feedlot manure is stored in aerobic conditions, and so the INRA/IPCC fit for manure emission was poorer (P  4 was very close between methods to that for total CH 4 ( P  = 0.39), enteric CH 4 representing 93% of total emissions. The main improvement is the use of a robust equation (from numerous data and diets), based on digestible organic matter intake (DOMI) corrected for the digestive interactions, to predict CH 4 consistently from enteric and manure sources. It was developed for the French livestock inventory but is customizable for other countries. This new improved CH 4 estimation method, based on equations from a large literature database, complies with IPCC rules for a Tier 3 method.