2025-12-25

Japan International Research Center for Agricultural Sciences (JIRCAS)
National Agriculture and Food Research Organization (NARO)

JIRCAS and NARO conducted an integrated assessment using Ishigaki Island, Okinawa Prefecture, as a model for tropical and subtropical island regions, to visualize how the actions of producers and consumers influence nitrogen balance optimization through the Food Nitrogen Footprint¹ methodology. This study aims to propose concrete nitrogen reduction strategies from Japan’s island regions to address the nitrogen problem, which is increasingly exceeding the Earth’s safe operating limits (planetary boundaries).

Nitrogen is essential for crop production; however, excessive reliance on chemical fertilizers has hindered the use of organic resources such as compost, thereby contributing to increased agricultural nitrogen loads². In addition, diets centered on animal-based protein and rising food loss further exacerbate nitrogen burdens across the entire food system. These challenges highlight the need to reassess nitrogen cycling from both production and consumption perspectives.

In this study, Ishigaki Island—where agriculture and livestock production are prominent—was used as a case study to examine concrete nitrogen reduction measures in Japan. By applying the Food Nitrogen Footprint approach, researchers quantitatively assessed nitrogen inputs³ and nitrogen loads associated with food and feed flows both within and beyond the island. The evaluation integrated measures on the producer side and consumer side. Specifically, the study explored scenarios in which producers promote the return of cattle manure compost to farmland, while consumers shift toward plant-based protein diets, reduce food loss, and recycle food loss into livestock feed. The effects of these measures on the island’s overall nitrogen balance—focusing on both nitrogen inputs and nitrogen loads—were then quantitatively evaluated.

The results showed that, on the producer side, chemical fertilizer use and nitrogen loads within the island could be reduced by 20% and 13%, respectively. On the consumer side, nitrogen inputs and nitrogen loads outside the island could potentially be reduced by 19% and 31%, respectively. These findings indicate that combined efforts by producers and consumers can generate synergistic effects in reducing nitrogen inputs and loads both inside and outside the island.

This study represents the first attempt to integratively evaluate production and consumption within a single framework. It demonstrates that addressing only one side is insufficient and underscores the importance of collaboration between producers and consumers for optimizing nitrogen cycling at the global scale. The findings provide concrete, collaborative solutions originating from island regions and are applicable not only to Ishigaki Island but also to other tropical and subtropical island regions, such as the Philippines. Through the development of sustainable food systems, the study is expected to contribute to achieving the United Nations Sustainable Development Goals (SDGs).

The results of this research have been published as an open-access article in the online version of Environmental Research Letters on October 10, 2025.

Related Information

Funding

Operating Expenses Grant Project:
“Development and evaluation of environmental conservation technologies for tropical islands through an approach emphasizing Yama-Sato-Umi (Ridge-to-reef agroecosystem) connectivity”

Authors

HAMADA Kosuke, EGUCHI Sadao, HIRANO Nanae, ASADA Kei

Paper Title

Simultaneous production and consumer efforts reduce the nitrogen load in a Japanese island’s food system

Journal Title

Environmental Research Letters
DOI: https://doi.org/10.1088/1748-9326/ae0b95

JIRCAS President: KOYAMA Osamu

Program Director:

HAYASHI Keiichi

Research Staff:

HAMADA Kosuke (TARF, JIRCAS)
EGUCHI Sadao, HIRANO Nanae, ASADA Kei (Institute for Agro-Environmental Sciences, NARO) 

Press Coordinator:

OMORI Keisuke (Head, Information and Public Relations Office)
Press e-mail: koho-jircas@ml.affrc.go.jp