First approach to the Japanese nitrogen footprint model to predict the loss of nitrogen to the environment
Humans increase the amount of reactive nitrogen (all N species except N2) in the environment through a number of processes, primarily food and energy production. Once in the environment, excess reactive nitrogen may cause a host of various environmental problems. Understanding and controlling individual nitrogen footprints is important for preserving environmental and human health. In this paper we present the per capita nitrogen footprint of Japan. We considered the effect of the international trade of food and feed, and the impact of dietary preferences among different consumer age groups. Our results indicate that the current average per capita N footprint in Japan considering trade is 28.1 kg N capita−1 yr−1. This footprint is dominated by food (25.6 kg N capita−1 yr−1), with the remainder coming from the housing, transportation, and goods and services sectors. The difference in food choices and intake between age groups strongly affected the food N footprint. Younger age groups tend to consume more meat and less fish, which leads to a larger food N footprint (e.g., 27.5 kg N capita−1 yr−1 for ages 20 to 29) than for older age groups (e.g., 23.0 kg N capita−1 yr−1 for ages over 70). The consideration of food and feed imports to Japan reduced the per capita N footprint from 37.0 kg N capita−1 yr−1 to 28.1 kg N capita−1 yr−1. The majority of the imported food had lower virtual N factors (i.e., Nr loss factors for food production), indicating that less N is released to the environment during the respective food production processes. Since Japan relies on imported food (ca. 61%) more than food produced domestically, much of the N losses associated with the food products is released in exporting countries.