Greenhouse gas emissions and land use from confinement dairy farms in the Guanzhong plain of China - using a life cycle assessment approach

The objective of this study were to quantify greenhouse gas (GHG) emissions and land use of milk production and evaluate the potential mitigation options at farm level in the Guanzhong plain, which is the main dairy farming region in China. The life cycle assessment methodology was used to analyse the GHG emissions of eight confinement dairy farms that covered different milk production levels, herd structures and diet compositions. The GHG emission per kg of fat and protein corrected milk (FPCM) ranged from 1.31 to 2.08 kg CO2 eq. after farm GHG emissions had been allocated to milk, meat and manure. Enteric methane and emissions related to feed production and manure management were the three major GHG emission sources from the eight farms and contributed 54%-60%, 21%-30% and 8%-10%, respectively, to total emissions. Land use per kg of FPCM was 1.81 m2 with the largest contribution from feed production. GHG emissions associated with the production of per kg of FPCM decreased with increasing herd milk productivity and herd feed efficiency. Sensitivity analyses showed that the GHG emissions were significantly affected by metric values of global warming potential (GWP), with increases of about 4% and 12% for the calculation based on the IPCC (2013) GWP values, compared to IPCC (2007) and IPCC (1996) values, respectively; and soybean meal from imported soybeans would increase GHG emissions per kg of FPCM significantly due to the emissions related to land use change. Lowering N-fertilizer use per ha for feed crop production, improving milk productivity and herd structure, and encouraging farmers to use manure for crop production are promising abatement strategies. Due to the low percentage of grass (average 14%) in the diet for dairy cows in the Guanzhong plain, replacing part of the concentrates with alfalfa hay would increase milk productivity and decrease GHG emissions per kg of FPCM.