A carbon footprint analysis was conducted for cultivation and harvesting of feed rations used for the production of dairy milk in the U.S. The goal is to determine the greenhouse (GHG) emissions on a basis of 1 kg of ration harvested or produced (kg CO2eq. / kg of feed rations) in the U.S on a regional basis and to make recommendations to reduce GHG emissions from the crop production chain.
Commonly used dairy feedstuffs in the U.S. such as soybeans, corn grain/silage alfalfa, etc were identified based on a recent literature review and information from dairy farm surveys. By dividing the U.S into five dairy regions the following input data for the cultivation and harvesting of dairy rations were collected for each region; crop production data, energy input, soil amendments, and crop protection chemicals. Life cycle inventory (LCI) data for these inputs were mainly collected from the USDA National Agricultural Statistical Service on a state-by-state basis as well as from state extension services forage crop budget estimates. Apart from consulting other LCA studies and published articles and reports, this cradle-to-farm gate GHG impact analysis was conducted utilizing the EcoInvent unit processes in SimaPro version 7.1©.
The final GHG results (kg CO2 eq. / kg of feed ration) varied regionally depending on a number of factors such as the lime and fertilizer application rates. The average national U.S. GHG results of the main crops are as follows: corn grain (0. 331), corn silage (0.071), dry distiller grains (0.818), wet distiller grains (0.268), oats (0.736), soybeans (0.344), soybean meal (0.406), winter wheat (0.395), alfalfa hay (0.147) and forage mix (0.137).
Dairy production region 2 (the southeast) generally showed a relatively high level of carbon footprint for most crops grown locally and this can be attributed mostly to the higher application rates of both synthetic fertilizers and lime. The highest contributor to carbon footprint for most regions (apart from soybean) was identified to be the application of inorganic N fertilizer. Finally, efficient transfer of knowledge to farmers with regards to Fertilizer Best Management Practices such as precision application of farm nutrients as well as efficient management of crop residues can contribute significantly to reduce the regional carbon footprints.