Changes in the nitrogen footprint of green tea consumption in Japan from 1965 to 2016.

Heavy application of nitrogen (N) in tea (Camellia sinensis (L.)) plantations causes various environmental problems. To date, studies on N flows have been limited to the tea plantation level, but the crucial drivers of N flows are consumers, not farmers. Therefore, this study aimed to evaluate changes in N flows concerning green tea production and consumption in Japan from 1965 to 2016 using the N footprint concept. Nitrogen use efficiency (NUE), virtual N factor (VNF), and N footprint were calculated using a Monte Carlo method from data for 17 parameters obtained from the literature review. The VNF for green tea in Japan decreased from 54.5 in 1991 to 30.8 in 2016. The major reasons for this decrease were (i) increased NUE in plantations and (ii) increased consumption of ready-to-drink (RTD) tea, matcha, and powdered tea, indicating an increase in the efficiency of N intake from green tea by consumers. The decrease in VNF resulted in a reduction in N footprint from green tea consumption. However, the decline in N footprint since 2004 is not derived from the decrease in VNF but mainly from reduced green tea consumption. A sensitivity analysis revealed that the parameters associated with the extraction efficiency of tea, powdered tea production, and the amount of tea leaves used for RTD production strongly affected VNF estimation.