4.7 Article

Nutrient-extended input-output (NutrIO) method for the food nitrogen footprint

Journal

ENVIRONMENTAL RESEARCH LETTERS
Volume 16, Issue 11, Pages -

Publisher

IOP Publishing Ltd
DOI: 10.1088/1748-9326/ac2c35

Keywords

nutrient use efficiency; supply chains; agro-food systems; material flow analysis; input-output analysis

Funding

  1. JSPS KAKENHI [JP17H00794, JP19K20496]
  2. Research Institute for Humanity and Nature [14200135, 14200156]

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Agro-food systems require nutrient input from various sources, but the loss of nutrients in supply chains poses a threat to human and ecosystem health. A novel NutrIO method is proposed to evaluate direct and indirect nutrient inputs throughout the supply chains, providing quantitative insights for improving nutrient use efficiency in agro-food supply chains.
Agro-food systems require nutrient input from several sources to provide food products and food-related services. Many of the nutrients are lost to the environment during supply chains, potentially threatening human and ecosystem health. Countries therefore need to reduce their nutrient/nitrogen footprints. These footprints are importantly affected by links between sectors. However, existing assessments omit the links between sectors, especially between the agriculture, manufacturing, and energy sectors. We propose a novel approach called the nutrient-extended input-output (NutrIO) method to determine the nutrient footprint as a sum of direct and indirect inputs throughout the supply chains from different sources of nutrients. The NutrIO method is based on a nutrient-based material flow analysis linked to economic transactions. Applying this method, we estimated the nitrogen footprint of Japan in 2011 at 21.8 kg-N capita(-1)yr(-1): 9.7 kg-N capita(-1) yr(-1) sourced from new nitrogen for agriculture and fisheries, 7.0 kg-N capita(-1) yr(-1) from recycled nitrogen as organic fertilizers, and 5.1 kg-N capita(-1) yr(-1) from industrial nitrogen for chemical industries other than fertilizers. A further annexed 55.4 kg-N capita(-1) yr(-1) of unintended nitrogen input was sourced from fossil fuels for energy production. The nitrogen intensity of the wheat and barley cultivation sector, at 1.50 kg-N per thousand Japanese yen (JPY) production, was much higher than that of the 0.12 kg-N per thousand JPY production for the rice cultivation sector. Industrial nitrogen accounted for 2%-7% of the nitrogen footprint of each major food-related sector. The NutrIO nitrogen footprint sourced from new nitrogen for agriculture and fisheries, at 8.6 kg-N capita(-1) yr(-1) for domestic final products, is comparable to the food nitrogen footprint calculated by other methods, at 8.5-10.5 kg-N capita(-1) yr(-1). The NutrIO method provides quantitative insights for all stakeholders of food consumption and production to improve the nutrient use efficiencies of agro-food supply chains.

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