Nitrogen loss to the environment due to various nitrogen-use efficiencies during milk and beef production in Japan

Reactive nitrogen (Nr) is essential to livestock production, but its excess use can become a source of environment pollution, the extent of which can be evaluated by using a nitrogen (N) footprint model. Such a model provides a useful indicator linking consumers' activity with Nr loss to the environment. To reduce Nr losses, it is crucial to reduce the use of 'new-Nr,' namely Nr chemically (synthetic-Nr) and biologically (BNF-Nr) fixed from the atmosphere, by recycling manure-Nr for crop production. When estimating the N footprint associated with the N use efficiency (NUE) of animal products and virtual N factor (VNF), namely the ratio of Nr released to the environment during the food production and consumption processes per unit Nr consumed, Nr flows from feed production in fields to milk and beef consumption by humans should be quantified. Here, we estimated the national-scale NUE of milk and beef production in Japan and quantified the VNF and N footprint, namely Nr losses to the environment per capita through milk and beef consumption by humans. Crop NUE (i.e. feed-Nr/(new-Nr + manure-Nr)) was greater in paddy fields and grassland than in upland fields. Milk NUE (i.e. consumed-Nr/new-Nr) and milk VNF were 15% and 5.6, respectively. Beef NUEs (i.e. consumed-Nr/new-Nr) and beef VNFs were 4.0% and 24.2 for dairy bullocks, 3.2% and 29.8 for crossbred cattle, and 2.4% and 41.5 for beef breeds, respectively. The length of the fattening period was an important determinant of beef NUE and beef VNF. When the components of slaughtered cattle (the three types previously mentioned + culled cattle) in Japan were considered, beef NUE and beef VNF were 3.7% and 26.3, respectively. We hope that providing consumers with this information will prompt them to choose more environmentally sustainable animal products and thus substantially reduce the worldwide N footprint. (paper)