Virtual nitrogen factors and nitrogen footprints associated with nitrogen loss and food wastage of China’s main food crops
A nitrogen (N) flow, divided into production, food supply, and consumption phases, was designed to calculate the virtual N factors (VNFs) and N footprints (NFs) of China's main food crops. It covered four food groups—cereals, tubers, vegetables, and fruits—comprising 24 food crops. A meta-analysis of 4896 relevant examples from 443 publications was conducted to build a database on N availability and N loss rates during each stage. We calculated N loss from each food group during each phase, and estimated VNFs and NFs based on N loss. It was found that 39.2%–67.6% of N inputs were lost during the production phase, 6.6%–15.2% during the food supply phase, and 0.9%–6.7% during the consumption phase. VNFs for cereals, tubers, vegetables, and fruits were 2.1, 2.9, 4.1 and 8.6, respectively. To raise public awareness, we also calculated the NFs, which were 30.9, 6.7, 7.4, and 17.2 g N kg−1 for cereals, tubers, vegetables, and fruits consumed, respectively, equal to 9.3 kg N capita−1 yr−1 consumption for these four food crops in China. We concluded that policies and strategies to reduce N loss, especially N loss embedded in food loss, must be taken into account to improve the technologies, infrastructure, approaches, and social awareness in reducing nutrient loss during food production and consumption phases.