What is the best use of oil from cotton (Gossypium spp.) and canola (Brassica spp.) for reducing net greenhouse gas emissions: biodiesel, or as a feed for cattle?

Abstract

Cotton (Gossypium spp.) and canola (Brassica spp.) are significant crops worldwide. Vegetable oil extracted from the seed of these crops offers the potential to reduce greenhouse gas emissions (GHG) through conversion into biodiesel to displace GHG associated with fossil-fuel diesel, or, by feeding the oil to cattle to reduce enteric methane emissions. Estimations of the net GHG effects of these two alternative uses of vegetable oil from cottonseed and canola were made in the present study for Australian conditions, using data from the literature and empirical data from livestock experiments. Results from the present study, which used a GHG accounting approach, indicated that feeding canola oil (as canola meal with 10.4% oil concentration) to cattle resulted in a net increase in GHG. However, GHG abatement from biodiesel produced from the oil (associated with the production of this same canola meal) exceeded the net increase in GHG from feeding the canola meal by-product to cattle. This means that there would be an overall GHG abatement from the combination of converting canola oil into biodiesel and feeding the resultant canola meal (with 10.4% oil concentration) to cattle. Feeding cottonseed oil in a supplement to cattle (whole cottonseed with 22% oil concentration) was estimated to result in GHG abatement, but to a lesser degree than would conversion into biodiesel. In both cases, major determinants of the GHG balance were the emissions arising from long-distance transport of the high-oil supplementary feeds fed to cattle, or of biodiesel to end-users.