Regional inventory of methane and nitrous oxide emission from ruminant livestock in the Basque Country

Ruminant livestock systems emit CH4 and N2O to the atmosphere. Quantification of greenhouse gas (GHG) emissions in Spain is reported annually in the National Emission Inventory. The objective of this study was to update the annual CH4 and N2O emissions by dairy and beef cattle, and dairy ewes in the Basque Country of Northern Spain according to the recommendations of IPCC (2006) (Tier 2) using regional farm management data. A mathematical approach was used to assess uncertainties of estimated emission factors (EF). CH4 EF from enteric fermentation was 107 kg CH4/hd/yr for dairy cattle with a milk yield of 7870 kg milk/hd/yr. The corresponding values for beef cows and dairy ewes were 60 and 8.4 kg CH4/hd/yr. Emission of CH4 from enteric fermentation accounted for 87% of total CH4 emissions in ruminant production, with dairy and beef cattle the main contributors. The regional contribution of beef cattle to enteric CH4 emissions has become important recently as many farmers have changed from dairy to beef cattle production. CH4 EF (Tier 2) from manure management was 33.2, 2.0 and 0.3 kg CH4/hd/yr for dairy cattle, beef cattle and dairy ewes. From 2005, many small dairy cow farms (<20 livestock units) have closed and manure management has become mostly liquid slurry resulting in higher CH4 emissions. The EF of N2O from manure management was 1.0, 1.4 and 0.1 kg N2O/hd/yr for dairy cattle, beef cattle and dairy ewes. EF values calculated from Tier 2 were higher than those from Tier 1, except for dairy cattle EF from enteric fermentation, since these animals are mainly fed high concentrate diets with high digestibility which result in lower enteric CH4 emissions/hd. By improving livestock characterization we obtained lower uncertainties for EF calculated as Tier 2 than for default values from Tier 1. Emissions from manure management had the largest uncertainty, and the uncertainty of N2O EF from manure management was higher than for enteric CH4 EF due to its high natural variability and poor knowledge of it. The animal category with the lowest uncertainty was dairy cattle, as more accurate data were available due to it largely being in intensified production systems. aper 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.