Modelling of on-farm greenhouse gas emissions from dual-purpose meat and wool sheep production in different geographical regions of Norway

The whole-farm model, HolosNorSheep, was developed to estimate net greenhouse gas emissions from dual purpose sheep production in Norway. The model adopted a cradle-to-farm gate system boundary and is based on the International Panel on Climate Change methodology and includes direct emissions from enteric and manure methane (CH₄; GWP₁₀₀=27), direct and indirect nitrous oxide (N₂O; GWP₁₀₀=273) from manure and soils, direct carbon dioxide (CO₂) emissions from energy use and indirect CO₂ emissions from the production of input factors. Soil carbon balance is calculated using the ICBM-model. Emission intensities (CO₂-eq/kg product) for sheep carcass and greasy wool, was estimated for five geographical regions of Norway (East, West, South, Mid and North). The geographical regions varied considerably in climate, feed resources, days on pasture and herd/farm management. Estimated emission intensities per kg carcass and greasy wool varied from 23.5 to 19.9 (Mid region) to 26.8 and 22.8 kg CO₂-eq (North region) respectively. The difference between the Mid and North region was mainly due to higher CO₂ and N₂O emissions from use of fuel and N-fertilizer in the North, where a short growth season, and thus reduced grass yields, are compensated by using greater land area. Based on the distribution of sheep in the regions, and the emission intensities in each region, weighted average emission intensities per kg carcass and greasy wool were estimated as 25.1 and 23.3 kg CO₂-eq, respectively. Five alternative methods for the allocation of the co-products were compared with the amounts allocated to greasy wool ranging from 0 % when using no allocation (i.e., all emissions allocated to the sheep carcass), 11 % for economic allocation, 12 % for mass allocation, 19 % for biophysical allocation based on energy requirement up to 31 % for allocation based on protein mass. The emission intensity for wool was highly sensitive to the allocation method used (range from 0 to 61 kg CO₂-eq per kg greasy wool), while the effect on sheep carcass was lower (range 19 to 28 kg CO₂-eq per kg carcass). For production systems where meat is the main product, as in Norway, allocation should be based on biophysical allocation based on energy requirement.