Greenhouse gas emissions from enteric fermentation and manure on organic and conventional dairy farms - an analysis based on farm network data

Feed and manure composition and qualities in an organic and conventional dairy farm network in Germany (22 farm pairs) were analysed. Related greenhouse gas (GHG) emissions from enteric fermentation and from animal excretions were calculated by using two methods each. Feeding and feedstuff quality were farm specific. On average, organic dairy cows received significantly less concentrates, maize silage and straw and significantly more pasture and hay than conventional dairy cows. No differences were found for feeding grass silage. Results for methane (CH4) emissions from enteric fermentation depended strongly on the calculation methodology. They were higher when feed quality was considered as an input parameter (average GHG emissions 3822 and 3759 kg CO2-eq. cow-1 a-1 on organic and conventional farms) as opposed to when only feed intake was considered (2852 and 3112 kg CO2-eq. cow-1 a-1). Differences between the methods were particularly prominent when high amounts of fibre-rich feedstuff were used and, with regard to product-related emissions, at lower milk yields. GHG emissions from manure are also directly connected with feed intake and quality. Manure qualities and storage conditions on the farms were highly variable. On average, the related GHG emission potential was similar in liquid and solid manures (32 kg CO2-eq.t-1 fresh matter). Since feed quality management on farms influences milk yield, enteric CH4 emissions and manure composition, it should be part of advisory concepts that aim at reducing GHG emissions in milk production. Technical changes inmanure storage and handling offer an additional GHG reduction potential.