The relationship between greenhouse gas emissions and the intensity of milk production in Ireland

European Union agri-environmental schemes aim to reduce the environmental impact of agricultural production, but were developed before consideration of greenhouse gas emissions from agriculture. Life cycle assessment methodology provided a framework for comparing emissions as kg CO2 equivalent per kg of energy corrected milk (ECM) (kg CO2 kg(-1) ECM yr(-1)) and per hectare (kg CO2 ha(-1) yr(-1)) for farms both within and outside the Irish agri-environmental scheme. The agri-environmental scheme farms operate extensive systems from 40 to 120 cows producing between 3032 and 5946 kg ECM cow(-1) lactation(-1). The cows are fed on grass, conserved silage, and concentrates. Supplementation ranged between 250 and 620 kg cow(-1) yr(-1). The conventional farms had between 30 and 77 milking cows producing 4736 to 6944 kg ECM cow(-1) lactation(-1). Supplementation ranged from 400 to 1000 kg cow-' yr-1. The emissions from each unit were estimated using published emissions factors and possible error was evaluated by using ranges for each factor. Calculated emissions ranged from 0.92 to 1.51 kg CO2 kg(-1) ECM yr(-1) and 5924 to 8323 kg CO2 ha(-1). On average, total emissions from conventional farms were around 18% (p = 0.01) greater than the agri-environmental scheme farms and emissions per hectare (total area required) were 17% greater (p = 0.02) but there was no significant difference (p = 0.335) in terms of emission per unit milk produced. To evaluate greenhouse gas emissions for each farm in terms of the system intensity it was necessary to define a measure of intensification and area per liter of milk produced that was best.