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Article

Scenario Analysis of Japan’s Food and Feed Systems: Integrating Nutrient Flows with Sustainable Agricultural Policy

by
Kimiko Ushiyama
* and
Masao Takano
Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8601, Japan
*
Author to whom correspondence should be addressed.
Sustainability 2026, 18(11), 5710; https://doi.org/10.3390/su18115710
Submission received: 21 April 2026 / Revised: 23 May 2026 / Accepted: 28 May 2026 / Published: 4 June 2026
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Abstract

Recently, the Japanese government has introduced ambitious policies for agricultural sustainability, specifically the MIDORI Strategy, aimed at reducing chemical fertilizer use, expanding organic farmland, and increasing calorie-based food self-sufficiency. To evaluate the feasibility of these goals, this study quantified nitrogen and phosphorus flows within the 2021 food and feed system using a normalized “Nutrient Index”. A scenario analysis was conducted using policy targets as parameters, where currently non-circulated waste streams were modeled as potential sources for domestic nutrient recovery. The results indicate that Scenario A (a 30% reduction of chemical fertilizers) is the most feasible, achieving significant improvements in circulation ratios through recovery of nutrients from sewage and livestock waste. While Scenario B (increasing organic farmland) shows similar trends, its success depends on technological advancements to mitigate the yield gap between organic and conventional systems. Scenario C (increasing calorie-based food self-sufficiency) presents the greatest challenge: maintaining current dietary patterns requires a great shift in nutrient recovery from waste. However, shifting dietary habits toward higher domestic rice consumption (Scenario C-2) significantly mitigates land and fertilizer demand. Achieving these targets requires a holistic approach that integrates technological infrastructure with socio-political shifts in land use planning and consumer behavior.

1. Introduction

Nitrogen and phosphorus play a vital role in human society across the entire food and feed system, from production and consumption to disposal and circulation. In agricultural production, the development of chemical fertilizers containing these nutrients triggered the “Green Revolution”, which significantly increased yields and supported global population growth. Consequently, global fertilizer demand has risen steadily since the 1960s [1,2] and is predicted to continue growing [3,4]. However, current practices are unsustainable. Nitrogen fertilizer production is energy intensive and relies heavily on fossil fuels, while phosphorus fertilizer is derived from finite mineral resources. These practices result in negative environmental impacts, including greenhouse gas emissions, eutrophication, and soil degradation. Under the “Planetary Boundaries” framework, researchers warn that the global use of nitrogen and phosphorus is nearing the planet’s ecological capacity [5]. Reducing chemical fertilizer use is therefore a critical challenge for agricultural sustainability and beyond. To address this, several strategies have been promoted, including improved nutrient management, the substitution of chemical fertilizers with organic alternatives, the promotion of organic farming, and the circular recovery of nitrogen and phosphorus from waste and wastewater [6].
This study focuses on Japan, a country facing unique challenges in its transition to sustainable agriculture [7,8]. While total fertilizer usage in Japan has been decreasing, the input trend of nitrogen and phosphorus fertilizer per unit of farmland has remained higher than the world average since the 1960s. Phosphorus input, in particular, is nearly four times the average of the United States, the EU, and the global average [9]. This is partly due to Japan’s volcanic soil, which contains high levels of aluminum that bind with phosphorus. To ensure crops take up sufficient nutrients, farmers often over-apply phosphorus to maintain “free” phosphorus in the soil [10]. Japan also faces significant resource security issues. The country relies heavily on imports for food, feed, and energy. Nearly all chemical fertilizer materials are imported, and self-sufficiency rates remain low: 27% for feed, 38% for calorie-based food, and only 13% for energy [11,12,13,14]. This reliance on trade impacts global sustainability through “virtual water and nutrient flow”, where the resources used for production are effectively exported from the origin country [15,16]. Furthermore, because Japan imports more than it supplies domestically, it must treat the resulting nitrogen and phosphorus waste using imported fossil fuels. Although Japan has made significant strides in sewage treatment and water quality regulation to prevent eutrophication in rivers and enclosed seas over the last decade, these nutrients are not circulated back to the exporting countries [17]. This creates a nutrient imbalance, effectively preventing the natural circulation in countries that export these materials to Japan. Increasing self-sufficiency and reducing imports are essential steps for Japan to contribute to the sustainable, global-scale circulation of nitrogen and phosphorus.
Farmland area is the primary limiting factor for food production in Japan; therefore, land use changes must be considered in conjunction with shifts in nitrogen and phosphorus circulation. Approximately 70% of Japan’s land area consists of mountainous and forested terrain, which seriously limits the flat land available for agriculture, residential, commerce, and industrial use. Following the population growth and economic development of the post-World War II era, farmland has been further reduced through conversion to residential and industrial zones, as illustrated in Figure 1 [18,19].
In addition to the land-use changes, the reduction of farmland is also attributed to Japan’s declining population. In contrast to global trends, Japan’s population peaked in 2008 and is projected to continue decreasing due to a low birth rate [20]. Consequently, the agricultural population is both shrinking and aging, leading to an increase in abandoned farmland [21].
Government policies are essential for improving the sustainability of the nitrogen and phosphorus input–output balance [22]. The FAO’s “International Code of Conduct for the Sustainable Use and Management of Fertilizers” promotes the appropriate management of both chemical and organic fertilizers to mitigate global environmental issues such as climate change, biodiversity loss, and desertification [23,24]. While there is no global target for organic agriculture, the market for organic products and area of organic farmland are expanding [25]. For example, the EU’s “Farm to Fork Strategy” aims to reduce chemical fertilizer use by 20% and increase organic farmland to 25% by 2030 [26]. Similarly, the United States has launched the Agriculture Innovation Agenda, targeting a 40% increase in production and a 50% reduction in environmental footprint by 2050 [27]. There is also a target to reduce nutrient losses from agriculture by 30% by 2050 to improve water quality [28].
Japan’s Ministry of Agriculture, Forestry, and Fisheries (MAFF) introduced “MIDORI Strategy”, which aims to reduce chemical fertilizer use by 30% and expand organic farming to 25% of total farmland by 2050 [29]. Furthermore, the “Basic Plan for Food, Agriculture and Rural Areas” (revised in 2020 and 2025) targets a calorie-based food self-sufficiency of 45% [30,31]. However, the feasibility of these quantitative targets has not been fully explored in political or academic spheres [32]. It is essential to clarify the potential of alternative fertilizers to replace chemical input and to evaluate the farmland required to meet those goals. Previous scenario analyses have been conducted for chemical fertilizer reduction for several countries and regions [33,34]. However, they often focus solely on inputs and overlook the total food and feed system, including waste outputs.
Japan possesses highly developed municipal treatment facilities; approximately 93% of the population is connected to wastewater infrastructure, and household and industrial waste are managed through incineration or other treatment processes [35].
It is necessary to quantify the current state of nitrogen and phosphorus flows within this overall circulation before conducting the scenario analyses. Previous studies in Japan have quantified these flows, but data points vary and waste treatment outputs are rarely included. Furthermore, the most recent available data for nitrogen and phosphorus are from 2015 and 2016, respectively, necessitating an update [36,37].
The objective of this article is to quantify the current nitrogen and phosphorus flows throughout the entire Japanese food and feed system as of 2021. Based on these results, this study conducts a scenario analysis to evaluate the feasibility of government targets regarding chemical fertilizer reduction, organic farmland expansion, and food self-sufficiency improvement. It is hoped that these findings will support progress toward a sustainable food and feed system in Japan.

2. Materials and Methods

2.1. Nitrogen and Phosphorus Flow Calculation

To determine the current nitrogen and phosphorus flows in Japan’s food and feed system, government statistical data for 2021 were primarily utilized. Where 2021 data were unavailable, the most recent available datasets were used. The system is illustrated in Figure 2, with numbered items described in Table 1. Calculation methodology and references are provided in Supplementary Materials (Text S1).
As shown in Figure 2, imported fertilizer materials (4-1) enter the “Industry” sector, where chemical fertilizers are produced alongside domestic materials. Chemical fertilizers (4-2) and circulated fertilizers (4-3), comprising livestock compost manure and sewage sludge, are applied to farmland (4-6). This land produces domestic food (2-2) and feed (3-2). Livestock feeds (3-4) are supported by domestic (3-2), imported (3-1), and circulated feed (3-3). Food resources are derived from “Livestock” (2-3) and “Fisheries” (2-4), domestic crops (2-2), and imports (2-1). Some food resources are processed in “Industry” (2-6) and supplied to “Households” together with net food (2-5), which includes non-edible waste. From “Industry” and “Households,” wastewater (6-1) and food waste (6-2) are generated and treated in “Treatment Facilities.”
Within the connected population, 87% use sewage facilities and 10% use night soil treatment [35]. Treated wastewater (7-1) is discharged to watersheds (12), and generated sludge is landfilled (7-2), recycled as construction material or fuel, or circulated as fertilizer. More than 70% of industrial food waste is circulated as feed or fertilizer, but 92% of household food waste is incinerated in incineration facilities with other wastes [38]. Ash from incineration (7-3) is landfilled or recycled as construction material. Japan exports food and chemical fertilizer although much less than what it imports. In this article, recycled construction material is considered as “non-circulated”, along with land-filled wastes (13), because it cannot be used as circulated fertilizer.
Studies listed in Table 2 were reviewed and compared to verify the validity of data obtained in this study. It should be noted that this study includes discharges to the environment from treatment facilities, not considered in many previous studies.

2.2. Overview of the Scenario Analysis

A scenario analysis was conducted based on targets set by “MIDORI Strategy for Sustainable Food Systems” and “Basic Plan for Food, Agriculture and Rural Areas” [29,30]. Quantitative targets are summarized in Table 3. Three scenarios were considered: Scenario A is a reduction of chemical fertilizer use, Scenario B is an increase in organic farmland area, and Scenario C is an increase in calorie-based food self-sufficiency. For B and C, two patterns of sub-scenario were constituted, respectively. Scenario B-1 considers circulated, organic fertilizers obtain the same yield as chemical fertilizers, whereas scenario B-2 assumes less yield compared to conventional farming, following well-established average yield from organic farmland that is approximately 75% of that from conventional farming using chemical fertilizers [51]. Scenario C-1 maintains the same food composition as in 2021, while Scenario C-2 allows for changes in food composition. Required farmland area for Scenarios C-1 and C-2 were calculated based on how much production was increased for each crop. Details of each scenario are described in the Results section. Quantitative targets are compared using 2020 as the base year. Although changes in demand due to population decrease are not considered nor discussed in the policy, it was reflected in the scenario analysis to obtain more realistic analysis results. The projected population in 2050 is about 105 × 106, representing a 17% decrease from 2020 [20]. It was assumed that the demand for food decreases proportionally to the population change. Other aspects of socio-economic factors such as adaptation to climate change were not taken into account because this article focuses on the issues in the current system of nutrient circulation in society.

3. Results

3.1. Nitrogen and Phosphorus Flows in Japan (2021)

3.1.1. Calculated Flows in 2021

The calculated flow values for 2021 are presented in Table 4. For circulated fertilizers, denitrification, and non-circulated waste, additional details regarding the sources described in the flow diagram (Figure 2), such as sewage and livestock excreta, are indicated. Each flow value represents the annual weight per item. In this study, “Nutrient Index” is introduced, representing the ratio of each item relative to the “Food supply” to households (indicated as 2-7 in Figure 2). Specifically, the nitrogen and phosphorus flow values were divided by those of “Food supply (2-7).” This index was developed for this article to visualize and simplify the characteristics of the nutrient flow.

3.1.2. Input/Output Comparison

In many previous studies, an a priori balance between system inputs and outputs for each system was assumed, with these values often equalized by adding or subtracting arbitrary figures to achieve equilibrium. In contrast, this study separately calculated each item using corresponding statistical data, which were then aggregated for each system. Theoretically, the sum of these calculated inputs and outputs should be equal. To verify the accuracy of our analysis, the resulting inputs and outputs were compared for “Farmland,” “Households and Industry”, “Treatment facilities,” and Japan as a whole, as shown in Table 5.
In the “Farmland” sector, inputs consisted of fertilizers, biological nitrogen fixation (BNF), and atmospheric deposition, while outputs included denitrification (DN) from soil, crops for food and feed, as well as crop residuals. In this study, crop uptake accounted for 80% of nitrogen and 40% of phosphorus. Nitrogen inputs and outputs largely balanced, demonstrating the accuracy of the analysis; however, phosphorus inputs were significantly greater than outputs. This discrepancy may be attributed to phosphorus accumulation in the soil and leaching into groundwater. Conversely, nitrogen runoff was not observed, although it is generally known to occur in agricultural systems.
In “Livestock” sector, inputs consisted of feed, while outputs included livestock products and excreta. The latter is processed into circulated fertilizer (manure) and non-circulated waste, with DN occurring during manure production. Nitrogen inputs were lower than outputs, which may be attributed to statistical variance, as the nitrogen content in various feed crops had highly variable data. Phosphorus inputs and outputs were nearly equal.
In the “Households and Industry” sector, representing human society, inputs were net food and the food for processing to industry, while outputs consisted of wastewater and food waste. Inputs and outputs for both nitrogen and phosphorus were nearly equal. Regarding outputs, more than half of the nitrogen and phosphorus was discharged as wastewater, which exceeded the volume of solid waste.
For “Treatment Facilities”, inputs included wastewater, solid waste, and livestock excreta, while outputs consisted of treated water, circulated fertilizer and feed, non-circulated waste, and DN from the treatment process. Inputs and outputs were largely balanced for both nitrogen and phosphorus. Approximately half of the total input originated from livestock manure. Furthermore, nearly half of the nitrogen output was discharged into the atmosphere through denitrification and incineration.
For “Japan” as a whole, inputs consisted of imports, BNF, and deposition, while outputs included exports, nitrogen, and phosphorus present in watersheds, non-circulated waste, and DN. Nitrogen inputs and outputs were mostly equal; however, phosphorus showed discrepancy as seen in “Farmland”, indicating accumulation in the soil and leaching into groundwater.
To evaluate uncertainty of each flow, the output variance relative to the input was calculated, as presented in Table 6. Excluding phosphorus values for “Farmland” and “Japan”, where phosphorus accumulation remains uncertain, the overall uncertainty of the analysis was evaluated to be a maximum of 27%. This result is consistent with the previous study Hayashi et al. 2021, where a maximum uncertainty of 33% was considered [36].

3.1.3. Comparison with Previous Studies

The results presented in Table 4 were compared with previous studies listed in Table 2 to verify the validity of the values determined in this article. Figure 3 illustrates the historical nitrogen supply for food to households and feed to livestock in Japan, incorporating data from previous studies.
Figure 4 shows the nitrogen inputs to treatment facilities and the corresponding outputs of treated water; these figures demonstrate the effectiveness of the wastewater treatment process. Several studies indicated that feed supply exceeds food supply, implying that livestock consume more nitrogen and phosphorus than humans.
The values obtained in this study are within in the same range as those in other research, which demonstrates their validity. Calculation methods and references vary across studies. However, calculation errors were observed among the results even in separate studies that were conducted targeting the same year (Table 7). The coefficient value for nitrogen demonstrated a high degree of stability, remaining within the 24% range. In contrast, the phosphorus coefficient exhibited a higher degree of variability.

3.1.4. Simplified Flow Diagrams Based on the Nutrient Index

The nitrogen and phosphorus flow diagrams for the entire food and feed system, simplified and visualized using Nutrient Index, are shown in Figure 5 and Figure 6, respectively.
It should be noted that the index depends heavily on the food supply value, then the uncertainty of the food supply value affects all the indices. The uncertainty of the food supply is 24% at the maximum for nitrogen and 46% for phosphorous, respectively, as shown in Table 7. All indices carry these uncertainties. This is the imperfectness of the nutrient flow description with “Nutrient Index”; however, it is still useful to grasp the overall flow of nutrients with the precision of the one digit.
The following findings can be extracted from these diagrams.
Household food supply (2-7): Imports (2-1) support 40% of the nitrogen and 20% of the phosphorus in the household food supply. Domestic food (2-2) contributes 20% of the nitrogen and 40% of the phosphorus, while domestic livestock (2-3) provide an additional 20% of the nitrogen and 15% of the phosphorus.
Domestic livestock requirements and production: Domestic livestock (3-4) require a nitrogen supply three times greater—and a phosphorus supply ten times greater—than the household livestock supply (2-3). Livestock (3-4) consume 60% of the nitrogen and 100% of the phosphorus required by households (2-7). Approximately 30% of the feed supply (3-4) is supported by imported feed (3-1), and 80% to 90% of the total feed supply (3-4) is excreted as livestock waste (7-4).
Household outputs: From the “Households” sector, two-thirds of nutrient outputs are discharged as wastewater (6-1), and one third is discarded as solid food waste (6-2).
Treatment facilities: The total input to “Treatment Facilities” is 0.8 for nitrogen and 1.0 for phosphorus (relative to the Nutrient Index). Regarding nitrogen output, 75% of the input is discharged to the atmosphere (11-2), a volume three times greater than that of non-circulated waste (13). For phosphorus, three-quarters of the input (6-1 and 6-2) are disposed of as non-circulated waste (13).
Denitrification and incineration (11): Most losses are anthropogenic, originating from the incineration of food waste and aerobic treatment in sewage facilities.
Virtual nutrient dependency: “Virtual nitrogen” (the sum of imported nitrogen) amounts to 90% of household requirements, while “virtual phosphorus” reaches 160% of requirements (2-1, 3-1, and 4-1). These high values demonstrate that Japan’s food and feed system is heavily dependent on imported nutrients, posing a significant challenge for reduction efforts.

3.2. Results of the Scenario Analysis

3.2.1. Scenario Details

The results obtained for the year of 2021 were used as a control in the scenario analysis. For all scenarios, all items were deducted by 17%, which is the predicted population decline in 2050 before scenario manipulation. Table 8 provides the details for each scenario; specifying which items were manipulated and which remained unchanged. “Resulting items” refer to those values that changed accordingly in response to the manipulated parameters. Conversely, maintaining the demand and supply at the 2021 level constitutes a more conservative approach since predictions are subject to vary. The result with 2021 basis is provided in Supplementary Materials (Text S2) for reference.
In Scenario A, the total fertilizer supply reduced in conjunction with the same rate of population decrease, while the chemical fertilizer values were reduced to meet the quantitative target; consequently, the values of circulated fertilizer were increased. Imported fertilizer decreased in proportion to the reduction in chemical fertilizer. The additional circulated fertilizer was supplied from sewage sludge and livestock manure, which were previously categorized as non-circulated waste, thereby increasing nutrient circulation. Incinerated ash was not considered as a circulated fertilizer due to concerns regarding heavy metal contamination. When the chemical fertilizer supply was reduced by 30% across all farmland, the crop yields would not be affected [52].
In Scenario B, the total fertilizer supply and fertilizer application rate per hectare were held constant except for natural population decline. Circulated fertilizer was redirected to the expanded organic farmland area, and chemical fertilizer use was reduced accordingly. The supply of circulated fertilizer was managed using the same methodology as in Scenario A. Scenario B-1 assumes crop yields to remain unchanged, and scenario B-2 considers reduction of yield in organic farmland. Since total organic area is targeted as 1000 × 103 ha, additional farmland was considered conventional.
In Scenario C, an increase in food self-sufficiency was evaluated. Figure 7 illustrates the details of Scenario C regarding food composition and self-sufficiency rates [53]. Food composition is defined as the consumption ratio of rice, livestock products, oil, wheat, sugar, fish, vegetables, soybeans, fruits, and miscellaneous items. Scenario C was divided into two patterns: Scenario C-1 maintains current food composition but increases self-sufficiency rates, specifically in soybeans, wheat, oil, and livestock; Scenario C-2 modifies food composition by increasing the caloric intake of rice while reducing the consumption of livestock and oil, while maintaining the total caloric intake. The reductions in livestock and oil consumption are assumed to be achieved by reducing imports of these items, thereby increasing their domestic self-sufficiency. For Scenario C-1, imported food decreased due to the increased domestic harvest of soybeans, wheat, oilseeds (rapeseed), and livestock feed. The amount of fertilizer required for each crop was calculated based on the “Basis of Main Crops for Fertilization Application” by MAFF [54]. This scenario prioritizes the use of domestic feed and circulated fertilizer for the expanded farmland area. The increased demand for circulated fertilizer was met by utilizing non-circulated waste and the increased volume of livestock excreta. Scenario C-2, the reduction in oil and livestock consumption was subtracted from imported food totals, while the domestic harvest of rice was increased.

3.2.2. Results of the Scenario Analysis

The results of the scenario analysis for the following items, which demonstrate the impacts of the manipulations in each scenario, are shown in Figure 8, Figure 9, Figure 10, Figure 11, Figure 12, Figure 13 and Figure 14: imports, domestic production, fertilizers, waste, and farmland area.
Scenario A aims to reduce chemical fertilizer use (4-2) while maintaining a constant total fertilizer supply to farmland (4-6); consequently, the volume of circulated fertilizer (4-3) was increased. As shown in Figure 10, chemical fertilizer (4-2) use was reduced from 354.9 kt N/yr (Nutrient Index 0.37) to 248.4 kt N/yr (0.31) for nitrogen and from 140.6 kt P/yr (1.19) to 98.4 kt P/yr (1.00) for phosphorus—a 30% reduction as targeted in the MIDORI Strategy. With the prediction of population decline by 17%, more than half of the target is naturally accomplished. The ratio of circulated fertilizer to the total fertilizer supply expanded from 42% to 51% for nitrogen and from 46% to 55% for phosphorus. There is an increase in circulated fertilizer (4-3) by diverting nutrients from non-circulated waste (13), rising from 255.3 kt N/yr (0.27) to 260.6 kt N/yr (0.32) for nitrogen and from 119.0 kt P/yr (1.01) to 118.1 kt P/yr (1.20) for phosphorus (Figure 10). Because most of the chemical fertilizer in Japan is imported, the value of imported fertilizer (4-1) decreased, resulting in a reduction in total imports (1) of 25% for nitrogen and 27% for phosphorus (Figure 8). In this scenario, there were no changes to domestic production volumes or total farmland area.
Scenario B-1, representing an increase in organic farmland area, also maintains the total fertilizer supply (4-6) at a constant level on the basis of the assumption that the fertilizing effects of chemical and circulated fertilizers are equivalent. The same application rate (kg/ha) was applied to maintain the total domestic food and feed supply. It increases the use of circulated fertilizer (4-3) for organic farmland while decreasing chemical fertilizer supply (4-2). Circulated fertilizer (4-3) increased from 255.3 kt N/yr (Nutrient Index 0.27) to 300.8 kt N/yr (0.37) for nitrogen and 119.0 kt P/yr (1.01) to 134.1 kt P/yr (1.36) for phosphorus (Figure 10). Accordingly, chemical fertilizer (4-2) decreased from 354.9 kt N/yr (0.37) to 208.2 kt N/yr (0.26) for nitrogen and 140.6 kt P/yr (1.19) to 82.5 kt P/yr (0.84) for phosphorus. These results show a trend similar to Scenario A. The basis of Scenario B is the assumption that the fertilizing effects of chemical and circulated fertilizers are equivalent; therefore, the same application rate (kg/ha) was applied to maintain the total domestic food and feed supply.
Scenario B-2 represents an increase in organic farmland with 75% yield of conventional farming [51]. While the total farmland area remains unchanged in this scenario, 25% of it is converted to organic farming. A detailed consideration on required farmland, accounting for the yield gap between organic and conventional systems, is provided in the Discussion section.
Scenario C-1 increases calorie-based food self-sufficiency while keeping the total food supply (2-7), per capita caloric consumption (2265 kcal/day/capita), and food composition unchanged [53]. In this pattern, domestic production of soybeans, wheat, rapeseed oil, and livestock was increased to achieve higher self-sufficiency. Fertilizer for the increased crop production and feed for expanded livestock population were both sourced domestically. Imported food (2-1) decreased from 380.5 kt N/yr (0.37) to 266.5 kt N/yr (0.33) for nitrogen (a 30% reduction) and from 27.1 kt P/yr (0.19) to 15.7 kt P/yr (0.16) for phosphorus (a 42% reduction) (Figure 8). Domestic food (2-2) slightly decreased by 3% from 223.8 kt N/yr (0.23) to 216.1 kt N/yr (0.27) for nitrogen and from 43.1 kt P/yr (0.36) to 41.0 kt P/yr (0.42) by 5% for phosphorus. Domestic feed production, specifically corn and pasture, increased from 314.9 kt N/yr (0.33) to 523.8 kt N/yr (0.65) for nitrogen (a 66% increase) and from 58.1 kt P/yr (0.49) to 104.0 kt P/yr (1.05) for phosphorus (a 79% increase). The total farmland area required for this increased production was 4407 × 103 ha, about the same compared to 2021 (Figure 14). Only circulated fertilizer (4-3) was used for the additional farmland, from 255.3 kt N/yr (0.27) to 469.5 kt N/yr (0.58) for nitrogen and from 119.0 kt P/yr (1.01) to 200.3 kt P/yr (2.03) for phosphorus, resulting in an 84% increase for nitrogen and a 68% increase for phosphorus (Figure 10). The sources for this circulated fertilizer are existing “non-circulated” wastes, such as sewage sludge and livestock excreta, which are currently disposed of in landfills or recycled as construction material, as well as food waste collected prior to incineration (Figure 11).
Scenario C-2 also increases calorie-based food self-sufficiency and maintains the total food supply (2-7) but modifies the caloric composition to favor higher rice consumption and reduced oil and livestock consumption. Rice consumption was increased from 21% of the calorie consumption per capita to 31%; oil and livestock were decreased from 15% and 18% to 11% and 13%. Imported food (2-1) decreased from 380.5kt N/yr (Nutrient Index 0.37) to 243.2 kt N/yr (0.30), by 36%, for nitrogen and 27.1 kt P/yr (0.19) to 10.9 kt P/yr (0.11) for phosphorus, by 60% (Figure 8). Domestic food (2-2) decreased by 1% from 223.8ktN/yr (0.23) to 221.9 kt N/yr (0.28) for nitrogen and increased by 4% from 43.1kt P/yr (0.36) to 44.9kt P/yr (0.46) for phosphorus (Figure 9). As in Scenario C-1, only circulated fertilizer (4-3) was applied to the additional farmland but with significantly lower demand compared to C-1. Circulated fertilizer demand decreased from by 2% from 255.3 kt N/yr (0.27) to 249.3 kt N/yr (0.31) for nitrogen and increased by 5% from 119.0 kt P/yr (1.01) to 122.6 kt P/yr (1.24) for phosphorus, representing the smallest increase across all scenarios (Figure 10). The required farmland area was 4154 × 103 ha, a 4% decrease (Figure 14).
Each scenario contributes to an increase in the input and output circulation ratios, defined by the following equations.
Input Circulation Ratio (ICR) = Circulated Utilization/(Circulated utilization + Natural Resource Input)
Output Circulation Ratio (OCR) = Circulated Utilization/Waste Generation
The calculation methodology for the material circulation ratio was adapted from the “Environmental White Paper, Annual Report on the Environment, the Sound Material-Cycle Society, and Biodiversity in Japan”, utilizing nitrogen and phosphorus mass flows determined in this study [38].
The results for each scenario are presented in Table 9. The circulation ratios improved in all scenarios compared to the control. “Waste generation” refers to the total input to treatment facilities; thus, the OCR indicates the efficiency of nutrient recovery versus loss at these facilities. Nitrogen exhibits lower circulation ratios compared to phosphorus because of denitrification and incineration losses to the atmosphere within the nitrogen cycle. Scenario C-1 yielded the highest values for both ICR and OCR. Additionally, Scenario B resulted in higher ICR and OCR values compared to Scenario A and C-2.

4. Discussion

4.1. Current Nitrogen and Phosphorus Flows in Japan

By determining the nitrogen and phosphorus flows for Japan in 2021, this study identified significant imbalances and inefficiencies within the national food and feed system. These insights were made possible by the separate aggregation of inputs and outputs, which revealed the actual current status of nutrient movements rather than assuming a pre-existing equilibrium.
A substantial imbalance was observed in the national input–output profile. As a country with low self-sufficiency in fertilizers, food, and feed, Japan’s total imports, known as “virtual nutrients”, account for a Nutrient Index of 0.9 for nitrogen and 1.6 for phosphorus. In contrast, exports account for only 0.1 and 0.0, respectively, while the household food supply index stands at 1.0 for both. This massive disparity indicates that a large volume of imported virtual nutrients must be managed internally, requiring significant energy input to meet national environmental regulations. Furthermore, about 45% of phosphorus is lost throughout the system; it is assumed this nutrient accumulates within Japan, most likely in agricultural soils. Reducing heavy reliance on imported chemical fertilizers through domestic recovery would promote environmental sustainability and positively impact global virtual nutrient flows [56].
From a circulatory perspective, nutrient discharge into the atmosphere via denitrification (DN) and incineration, as well as runoff into watersheds, hinders total nutrient circulation. DN and incineration accounts for a Nutrient Index of 0.6, with the majority being anthropogenic emissions from treatment facilities. Combined, discharge and non-circulated waste reach a Nutrient Index of 0.3 for nitrogen and 0.8 for phosphorus. The ICR and OCR values demonstrate that Japan could achieve greater sustainability by enhancing circulation processes, especially in the nitrogen cycle.
Furthermore, specific “inefficiencies” are identified in farmland, livestock, and treatment facilities that currently obstruct nutrient circulation.

4.1.1. Farmland

Phosphorus fertilizer use is notably inefficient, with approximately 50% of applied fertilizers not reaching plant uptake due to soil accumulation or runoff. This is largely caused by the over-application of phosphorus, which chemically bonds with aluminum in Japanese soils [10]. In this study, the amount of annual phosphorus accumulation was estimated to be 145.2 kt P/year, which equals to 36.5 kg P/ha per cropped area. An agricultural soil monitoring review in Japan has reported that the average phosphorus is increasing overtime, exceeding the recommended required phosphorus amount by MAFF in “Basic Guidelines for Soil Productivity Improvement” [57,58].
Implementing customized fertilization plans based on local soil diagnostics can reduce chemical fertilizer use without compromising yields [59]. Additionally, advancements in precision management, such as optimized timing, slow-release fertilizers, and AI/IoT integration, offer pathways to improvement [60]. Enhanced-efficiency fertilizers, in particular, have demonstrated positive effects on yield, nutrient uptake, and the reduction of greenhouse gas emissions and water pollution [61,62].
In the policy, the development of new species that have higher fertile efficiency is expected towards 2050 [29]. Not only managing the application process, the biochemical approach is encouraged in long term view.
The effort to minimize phosphorus soil accumulation is also important from the aquatic environmental view. The water quality in rivers and closed ocean area are kept within the regulation value for more than 10 years [17]. Sometimes, nutrients are intentionally discharged from sewage facilities for protecting and feeding living organisms, for example, bivalves, in the coast area [63]. However, natural disasters, such as erosion due to heavy rain storms, could lead to run-off and eutrophication in the area [64].

4.1.2. Livestock

The nitrogen feed supply is three times the v5olume production, while phosphorus is six times higher. Although domestic livestock products represent only 20% of the nitrogen and 10% of the phosphorus in the total food supply, the feed required to produce them equals 60% of the nitrogen and 100% of the phosphorus in the human food supply. As shown in Figure 3, these findings align with previous studies. While composting livestock excreta is common, the ratio of feed input to final production remains inefficient. These inefficiencies are driving global movements toward diets with reduced meat consumption [65]. Potential recovery methods are illustrated in Figure 15. Technically, circulation could be improved through ammonia recovery from gases volatilized during composting, a process that has already shown effective fertilizing results (Figure 15a) [66].

4.1.3. Treatment Facilities

Approximately 60% of nitrogen relative to the human food supply is lost to the atmosphere during treatment. For phosphorus, a significant portion is not circulated but is instead landfilled or repurposed as non-circulated construction material. While over 80% of livestock manure is returned to farmland after via composting [67], food waste is typically incinerated, and sewage is treated aerobically. Currently, incinerated ash is recycled as construction material, not as fertilizer, and only about 10% of the generated sewage sludge by weight is circulated as fertilizer [68]. Directly circulating waste from treatment facilities to farmland as fertilizer is the most effective approach to accelerating nutrient circularity in Japan.
Government policies have been promoting to expand the use of sewage sludge utilization (Figure 15b); progress has been hindered by negative public perceptions toward heavy metals and hygiene, odor concerns, and distribution challenges [69]. However, as Table 10 indicates, the actual measurement of sewage sludges qualities are mostly within the tolerance values established in the policy [70].
The promotion of sludge utilization includes installing phosphorus recovery facilities to produce pure phosphorus fertilizer (Figure 15c), composting food waste prior to incineration (Figure 15. Diagram of potential nutrient recovery locations within treatment facilities where new technologies or facilities could be implemented: (a) ammonia recovery from volatilized gas during composting; (b) increased recycling of sewage sludge as circulated fertilizer; (c) installation of phosphorus recovery facilities; (d) composting of food waste as an alternative to incineration; (e) utilization of anaerobic digestion effluent as liquid fertilizer (Figure 15d), and implementing anaerobic treatment at sewage treatment facilities to produce liquid fertilizer (Figure 15e) [72]. Although they are currently implemented only in a few municipalities, they represent significant potential for widespread adoption [73].
As shown in Table 11, based on the total mass of nitrogen and phosphorus, it is currently impossible to replace 100% of chemical fertilizer demand with recovered circulated fertilizers alone. Furthermore, the fertilizing effect and resulting crop yields of circulated fertilizers remain a subject of debate, as they function differently with the soil matrix compared to synthetic options. Consequently, an equivalent weight of circulated fertilizer may not provide the same yield-stabilizing effects [74].
There are also documented risks associated with circulated fertilizers, including heavy metal accumulation and hygiene concerns [75,76]. To achieve higher levels of circularity, additional domestic sources, such as steel slags for phosphorus recovery or atmospheric ammonia synthesis, will be necessary [77]. Promoting the production and use of circulated fertilizer requires a three-fold approach; first, the modification of current waste treatment methods; second, the construction of new recovery facilities; third, the establishment of efficient distribution and matching systems between producers and farmers.
In EU, the trend of circular fertilizer is shifting from direct application of sewage sludge to phosphorus recovery through chemical and thermal treatment. Especially in Switzerland, also a country with a fairly low food self-sufficiency of 45% in 2021, a strict legislation has been implemented. The Japanese government should observe and ascertain the movement to determine the suitable way.

4.2. Findings from the Scenario Analysis

The scenario analysis, based on quantitative targets from current government policies, reveals the following:
Scenario A (Reducing chemical fertilizers): Reducing chemical fertilizer use requires a significant shift toward domestic waste resources, increasing the circulation ratio by approximately 20%. Realizing this scenario requires a shift in nutrient management strategies; chemical fertilizers are valued for their rapid nutrient release, whereas circulated fertilizers typically have a slower release profile. As discussed in Section 4.1, while soil diagnostic analysis is not yet widespread in Japan, transition to precision fertilizer planning based on soil conditions is essential to minimize the environmental runoff. Proper management is critical regardless of the fertilizer type, as the risk of runoff exists for both synthetic and organic sources [78].
Scenario B (Increasing Organic Farming): In scenario B-1, the circulation ratio increases by approximately 30% due to the increased application of circulated fertilizers, assuming total fertilizer supply and cropland area remain constant. In scenario B-2, the lower average yield of organic farming is accounted for. Therefore, total farmland area and chemical fertilizer use increased to maintain the national food supply. It remains unclear whether the MIDORI Strategy accounts for this yield gap. To compensate for the reduced yield from organic plots, an additional 270,000 hectares of conventional farmland using chemical fertilizer would be required. Consequently, the net reduction in chemical fertilizer use would be negligible.
Land use and organic farming: In this context, focusing solely on the expansion of organic farming areas does not directly lead to increased nutrient circulation. Furthermore, the relationship between organic farming and environmental load remains a subject of ongoing academic debate [79,80]. Policies promoting organic farming should be integrated with the development of advanced agricultural technologies, such as utilizing bio-char to increase crop yields [81] or leveraging mycorrhizal fungi inoculation to enhance nutrient uptake [82]. Development of pest control technologies utilizing physical and biological methods, new species resistant to diseases, and establishment of biotic pesticide are considered in MIDORI strategy [29]. Even the agricultural population has decreased; the trend is to create greater management body, leading to effective farming in terms of labor and machine usage [21].
Scenario C-1 (Self-Sufficiency via Current Diet): As demonstrated in Scenario C-1, increasing calorie-based self-sufficiency while maintaining the current food composition requires farmland area to the same degree as the current total. Although the current amount of farmland is sufficient, the ongoing shrinkage of the farmland area emphasizes the importance of government land-use management policies.
Due to the inherent inefficiencies of livestock production, increasing caloric self-sufficiency for meat requires doubling the current domestic feed production area. Expanding meat production also necessitates additional land and facilities for livestock management. To meet the resulting phosphorus demand, nearly 100% circulation of sewage sludge and livestock excreta would be required. As discussed in Section 4.1, food waste composting is not yet widespread; however, it must be promoted, as 100% circulation of current waste streams is otherwise unrealistic. Consequently, the feasibility of Scenario C-1 depends on significant infrastructure modifications and the social challenge of transforming food waste collection methods and incentivizing a return to agriculture labor to manage farmland [83].
Scenario C-2 (Self-Sufficiency via Dietary Shift): Scenario C-2, which achieves higher self-sufficiency by increasing rice consumption while decreasing meat and oil calories, requires significantly less farmland area because it eliminates the need for a massive increase in domestic feed production. In this scenario, the caloric composition was modified from the current levels (21% rice, 18% livestock, 15% oil) to 31% rice, 13% livestock, and 11% oil. Compared to 1965 when it was rice 44%, livestock and oil 6%, the modification does not look so great [53]. This simplifies to about 3 rice cups of cooked rice per capita; however, it becomes a challenge in today’s diverse dietary lifestyle [84]. Although the government policy predicts the same meat consumption amount per capita [31], the modification in food composition should also be considered to satisfy food self-sufficiency target with feasible farmland area. Although it is a big challenge to change a food diet that has shifted over time, the government could promote in this direction for a sustainable food and feed system with higher food self-sufficiency.
Figure 16 summarizes the feasibility of the proposed scenarios based on the “hard” (technological/infrastructural) and “soft” (socio-political) dimensions of social change. This framework directly reflects the challenges of promoting circulated fertilizer utilization discussed in Section 4.1. While Scenario C-1 achieved the highest circulation ratio, it presents the most significant barriers across both dimensions. To improve Japan’s food self-sufficiency, Scenario C-2 appears to be more viable, as it requires less intensive investment in new facilities and technology.
Socio-economic conditions, which were not manipulated in this analysis, may affect positively on the realization of the policy targets. The soaring price of fertilizer raw materials into Japan for the last couple of years could boost accomplishment of chemical fertilizers reduction, leading to expansion of circulated fertilizers from local organic waste. Due to the aging population, the food diet may shift back to a traditional style of more rice and less oil and meat. Preference for a healthy diet promotes rice flour consumption as breads and cakes.
Although not explicitly addressed in current national policies, land-use planning that prioritizes the expansion of farmland, potentially by constraining the expansion of residential or industrial areas, residential area is a critical factor for sustainable agriculture in Japan, where flat land area is a finite resource. Government policy should extend beyond setting key performance indicators (KPIs) to include integrated land-use planning and dietary recommendation to make these targets achievable. Finally, Scenario A offers the second highest circulation ratio with relatively low implementation barriers compared to other scenarios. Consequently, prioritizing the reduction of chemical fertilizers should be the primary focus for immediate policy enforcement.
In this article, the focus was on the KPI of MIDORI Strategy from the agricultural sector. It is an interdisciplinary approach where the policy targets the whole cycle of procurement, production, distribution, and consumption [29]. In particular for consumption, a lot of promotion and education are planned for a healthy food diet with domestic and organic production, including the development of applications for consumers to enhance physical condition. However, it lacks a concrete target and action plan for each individual consumer, which discourages consumers from change. The policy also financially supports building new facilities for circulated fertilizers. It is important to support planning the type of facilities that are the most applicable for the region. For the fertilizer management plan, the local planning based on stored data at agricultural research departments or experiment stations in each prefecture is also a crucial point for implementation.

5. Conclusions

This study quantified the 2021 nitrogen and phosphorus flows for Japan’s entire food and feed system using the “Nutrient Index,” a normalized indicator that allowed for a clear visualization of systemic imbalances.
  • Japan’s food system was highly import-dependent with “virtual” nitrogen about 90% and phosphorus 160% of household needs, while exports are very small.
  • In farmland, roughly half of the applied phosphorus fertilizers do not reach crops and are estimated to accumulate in soil or leach into groundwater, which connotes the risk of eutrophication upon erosion.
  • Livestock inefficiency exists because livestock consume similar to or greater than total human food requirements, where 80–90% of feed is excreted as waste.
  • By integrating the waste treatment sector into the nutrient flow, significant inefficiencies were identified, particularly regarding the loss of virtual nutrients to the atmosphere and landfills.
The scenario analysis evaluated the feasibility of current national sustainability targets, yielding the following conclusions:
  • Scenario A (Chemical Fertilizer Reduction): This remains the most feasible immediate policy. A 30% reduction in chemical fertilizer is achievable by strategically recovering non-circulated nutrients from sewage sludge and livestock waste.
  • Scenario B (Organic Farming Expansion): By considering two patterns of scenario B-1 with no gap and B-2 with 75% of conventional farming, the feasibility of this scenario was constrained by the “yield gap”. Without significant technological breakthroughs in organic agronomy (e.g., biochar or mycorrhizal fungi), expanding organic farming may inadvertently increase the demand for conventional land and fertilizers to maintain the national food supply.
  • Scenario C (Food Self-Sufficiency): Achieving higher self-sufficiency with current dietary patterns (Scenario C-1) is the most challenging goal for higher circulation requirement and management of farmland. However, scenario C-2 demonstrates that a dietary shift toward rice-based consumption can reconcile self-sufficiency targets.
To achieve a truly sustainable food and feed system, Japan must adopt a holistic approach that synchronizes waste treatment, land-use planning, and consumer dietary behavior. The government must look beyond quantitative KPIs and engage in proactive land-use management to protect farmland.
While this paper reviews national trends with limited conditions, the next essential step is to investigate these flows at the local level. Because a national goal is the sum of local actions, further research into regional spatial characteristics and prefecture-level supply-and-demand balances, building on recent work such as Mishima (2025), is required to provide a comprehensive roadmap for nutrient circularity in Japan [85]. A broader view to take in the effect of climate change, as well as socio-economic factors around food and feed system, which could not have been evaluated in this study, would lead to feasibility of the policy toward sustainability [86]. Furthermore, international comparison from circular condition and policy would add an important prospective.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/su18115710/s1, Text S1: Calculation methodologies and references; Text S2: The results of scenario analysis without population decline. References [87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110] are cited in Supplementary Materials.

Author Contributions

Conceptualization, K.U. and M.T.; Methodology, K.U.; Formal analysis, K.U.; Investigation, K.U.; Writing—original draft, K.U.; Writing—review & editing, M.T.; Visualization, K.U.; Supervision, M.T. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by “Nagoya University Knowledge Co-creation Program”.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available in FAOSTAT at https://www.fao.org/faostat/en/#data/RFN, e-Stat at https://www.e-stat.go.jp/, Standard Tables of Food Composition in Japan at https://www.mext.go.jp/en/policy/science_technology/policy/title01/detail01/1374030.htm and Comprehensive Website for Water Environment at https://water-pub.env.go.jp/water-pub/mizu-site/, all accessed on 20 April 2026.

Acknowledgments

Authors would like to thank Hiroki Tanikawa and Yasushi Maruyama from Nagoya University for their helpful review and feedback.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
ANREAgency for Natural Resources and Energy
BNFBiological nitrogen fixation
DNDenitrification
FAOSTATFood and Agricultural Organization Statistical Databases
GSIGeospatial Information Authority of Japan
ICRInput circulation ratio
MAFFMinistry of Agriculture, Forestry and Fisheries
MLITMinistry of Land, Infrastructure, Transport and Tourism
MOEMinistry of the Environment
MOJMinistry of Justice
OCROutput circulation ratio

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Figure 1. Farmland and residential area trends along with population.
Figure 1. Farmland and residential area trends along with population.
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Figure 2. Flow of food and feed system in Japan.
Figure 2. Flow of food and feed system in Japan.
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Figure 3. Historical trends in nitrogen supply for household food and livestock feed in Japan, based on previous studies (Table 2) and the current study.
Figure 3. Historical trends in nitrogen supply for household food and livestock feed in Japan, based on previous studies (Table 2) and the current study.
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Figure 4. Nitrogen inputs to treatment facilities and corresponding treated water outputs: a comparison of previous research (Table 2) and the current study results over time.
Figure 4. Nitrogen inputs to treatment facilities and corresponding treated water outputs: a comparison of previous research (Table 2) and the current study results over time.
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Figure 5. Nitrogen flow diagram highlighting the Nutrient Index in italics for each specific item.
Figure 5. Nitrogen flow diagram highlighting the Nutrient Index in italics for each specific item.
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Figure 6. Phosphorus flow diagram highlighting the Nutrient Index in italics for each specific item.
Figure 6. Phosphorus flow diagram highlighting the Nutrient Index in italics for each specific item.
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Figure 7. Details of Scenario C regarding food composition (kcal/day/capita) and corresponding food self-sufficiency rates: (A) represents food composition where oil, meat, and rice are manipulated for Scenario C-2; (B) shows the self-sufficiency rate for each category.
Figure 7. Details of Scenario C regarding food composition (kcal/day/capita) and corresponding food self-sufficiency rates: (A) represents food composition where oil, meat, and rice are manipulated for Scenario C-2; (B) shows the self-sufficiency rate for each category.
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Figure 8. Scenario analysis for nitrogen (A) and phosphorus (B) imports: resulting items include imported food, feed, and fertilizer.
Figure 8. Scenario analysis for nitrogen (A) and phosphorus (B) imports: resulting items include imported food, feed, and fertilizer.
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Figure 9. Scenario analysis for nitrogen (A) and phosphorus (B) domestic production: resulting items include domestic food, livestock products, and feed.
Figure 9. Scenario analysis for nitrogen (A) and phosphorus (B) domestic production: resulting items include domestic food, livestock products, and feed.
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Figure 10. Scenario analysis for nitrogen (A) and phosphorus (B) fertilizers relative to current demand: resulting items include chemical and circulated fertilizers.
Figure 10. Scenario analysis for nitrogen (A) and phosphorus (B) fertilizers relative to current demand: resulting items include chemical and circulated fertilizers.
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Figure 11. Scenario analysis for nitrogen (A) and phosphorus (B) waste from treatment facilities. The right side represents current circulation (the sum of circulated feed and fertilizer), while the left side shows currently non-circulated wastes, such as landfill.
Figure 11. Scenario analysis for nitrogen (A) and phosphorus (B) waste from treatment facilities. The right side represents current circulation (the sum of circulated feed and fertilizer), while the left side shows currently non-circulated wastes, such as landfill.
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Figure 12. Detailed flow diagram and results for treatment facilities. Input and output values are provided for food waste incineration facilities, sewage treatment facilities, and composting facilities for livestock manure.
Figure 12. Detailed flow diagram and results for treatment facilities. Input and output values are provided for food waste incineration facilities, sewage treatment facilities, and composting facilities for livestock manure.
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Figure 13. Scenario analysis results for nitrogen (A) and phosphorus (B) potential fertilizers. Current waste in the control—including sewage, livestock waste, food waste, and agricultural residuals—were determined as the potential source for increased circulated fertilizer demand in the scenarios. The potential source in Scenario C-1 increased due to the growth in domestic livestock production. The nitrogen loss ratio due to compost for circulated fertilizer production is set at 0.5 as waste recovery efficiency coefficient [55].
Figure 13. Scenario analysis results for nitrogen (A) and phosphorus (B) potential fertilizers. Current waste in the control—including sewage, livestock waste, food waste, and agricultural residuals—were determined as the potential source for increased circulated fertilizer demand in the scenarios. The potential source in Scenario C-1 increased due to the growth in domestic livestock production. The nitrogen loss ratio due to compost for circulated fertilizer production is set at 0.5 as waste recovery efficiency coefficient [55].
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Figure 14. Scenario analysis results for farmland area, illustrating total and the ratio of conventional to organic farmland. Current potential farmland, the sum of dilapidated farmland and unused residential area, is indicated as dot in the control.
Figure 14. Scenario analysis results for farmland area, illustrating total and the ratio of conventional to organic farmland. Current potential farmland, the sum of dilapidated farmland and unused residential area, is indicated as dot in the control.
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Figure 15. Diagram of potential nutrient recovery locations within treatment facilities where new technologies or facilities could be implemented: (a) ammonia recovery from volatilized gas during composting; (b) increased recycling of sewage sludge as circulated fertilizer; (c) installation of phosphorus recovery facilities; (d) composting of food waste as an alternative to incineration; (e) utilization of anaerobic digestion effluent as liquid fertilizer.
Figure 15. Diagram of potential nutrient recovery locations within treatment facilities where new technologies or facilities could be implemented: (a) ammonia recovery from volatilized gas during composting; (b) increased recycling of sewage sludge as circulated fertilizer; (c) installation of phosphorus recovery facilities; (d) composting of food waste as an alternative to incineration; (e) utilization of anaerobic digestion effluent as liquid fertilizer.
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Figure 16. Summary and feasibility assessment of scenarios: The requirements for scenario implementation are categorized into two types of challenges: “hard” (technological advancement and infrastructure modification) and “soft” (social change and policy adoption). The magnitude of implementation difficulty is indicated by arrows left and right, while feasibility of the scenarios is indicated by the vertical arrow. Based on this framework, Scenario A is identified as the most feasible, while Scenario C-1 presents the greatest overall challenge.
Figure 16. Summary and feasibility assessment of scenarios: The requirements for scenario implementation are categorized into two types of challenges: “hard” (technological advancement and infrastructure modification) and “soft” (social change and policy adoption). The magnitude of implementation difficulty is indicated by arrows left and right, while feasibility of the scenarios is indicated by the vertical arrow. Based on this framework, Scenario A is identified as the most feasible, while Scenario C-1 presents the greatest overall challenge.
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Table 1. Numbered items in Figure 2.
Table 1. Numbered items in Figure 2.
No.Item
1Import
2Food
3Feed
4Fertilizers
5Export
6Input to treatment facilities
7Output from treatment facilities
8Residuals from agriculture
9Biological nitrogen fixation (BNF)
10Deposition by rain
11Denitrification (DN) and incineration
12Watershed environment
13Non-circulated wastes
14Circulated wastes
Table 2. Referred previous studies.
Table 2. Referred previous studies.
ReferenceNitrogenPhosphorus
ANakanishi and Ukita, 1978 [39]-
BHakamata, 1996 [40]-
CMiwa et al., 2006 [41]-
DMatsumoto et al., 2017 [42]-
EMizutani, 1997 [43]Mizutani, 1997 [43]
FKawashima, 1996 [44]-
GTezuka et al., 2002 [45]Tezuka et al., 2002 [45]
HShindo et al., 2009 [46]-
ITakahashi, 2011 [47]Takahashi, 2011 [47]
JKatagiri et al., 2018 [48]-
KHayashi et al., 2021 [36]-
L-Matsubae, 2009 [49]
M-Nattorp et al., 2019 [37]
NCurrent studyCurrent study
Note: One study by Mishima and Kohyama 2010 [50] was excluded due to results being in different units.
Table 3. Scenarios and policy objectives.
Table 3. Scenarios and policy objectives.
ScenarioDescriptionStatus in 2021Policy Targets
ControlCalculated nitrogen and phosphate flow in 2021 (The result of 2.1)--
AChemical fertilizer reduction by 2050-30% reduction
B-1Organic farmland increase by 205027,000 ha, 0.7%Increase to 1,000,000 ha,
25% of total area
B-2Organic farmland increase by 2050 with low yield from organic farmland area
C-1Food self-sufficiency increase38%Increase food self-sufficiency to 45%
C-2Food self-sufficiency increase with food composition change
Scenario A through C reflect population decline by 17% in 2050.
Table 4. Calculated nitrogen and phosphorus flows and correspondent Nutrient Indices (ratios relative to household food supply).
Table 4. Calculated nitrogen and phosphorus flows and correspondent Nutrient Indices (ratios relative to household food supply).
No.ItemFlow Value (103 t/Year)Flow per Capita (kg/Cap/Year)Nutrient Index (-)
NPNPNP
1Import834.5192.26.651.530.871.63
2Food
2-1Imported food380.527.13.030.220.370.19
2-2Domestic food223.843.11.780.340.230.36
2-3Domestic livestock181.815.01.450.120.190.13
2-4Domestic fish103.58.30.820.070.110.07
2-5Net food742.290.55.910.720.770.77
2-6Food for processing221.027.71.760.220.230.23
2-7Food supply963.2118.27.670.941.001.00
3Feed
3-1Imported feed180.242.91.440.340.190.36
3-2Domestic feed314.958.12.510.460.330.49
3-3Circulated feed61.517.30.490.140.060.15
3-4Feed for livestock556.7118.24.440.940.581.00
4Fertilizers
4-1Imported fertilizers273.8122.22.180.970.281.03
4-2Chemical fertilizers354.9140.62.831.120.371.19
4-3Circulated fertilizers255.3119.02.030.950.271.01
4-4Circulated fertilizers from sewage sludge28.316.00.230.130.030.14
4-5Circulated fertilizers from livestock excreta212.883.41.700.660.220.71
4-6Fertilizer supply610.2259.64.862.070.632.20
5Export137.05.21.090.040.140.04
6Input to treatment facilities758.9116.66.050.930.790.99
6-1Wastewater595.170.64.740.560.620.60
6-2Wastes (domestic/industrial)163.845.91.310.370.170.39
6-3Livestock excreta generation523.6102.64.170.820.540.87
7Output from treatment facilities
7-1Treated water discharge
to watershed		197.315.41.570.120.200.13
7-2Sewage sludge95.450.10.760.400.100.42
7-3Incinerated ash-17.8-0.14-0.15
7-4Livestock excreta310.2102.52.470.820.320.87
8Residuals from agriculture102.613.10.820.100.110.11
9Biological nitrification in fields (BNF)86.7-0.69-0.09-
10Deposition by rain (whole land)556.0 4.43-0.58
10-1Deposition on farmlands64.0-0.51-0.07-
11Denitrification (DN) and Incineration615.6-4.90-0.64-
11-1DN from farmlands81.9-0.65-0.09-
11-2DN and Incineration
from treatment facilities		533.7-4.25-0.55-
11-3DN from sewage257.3-2.05-0.27-
11-4DN from livestock excreta compost212.8-1.70-0.22-
11-5Nitrogen from incineration63.5-0.51-0.07-
12Watershed environment417.328.23.330.220.430.24
13Non-circulated wastes164.471.01.310.570.170.60
13-1Non-circulated wastes
from sewage		67.134.10.530.270.070.29
13-2Non-circulated wastes
from livestock excreta		97.419.10.780.150.100.16
14Circulated Waste316.9136.32.521.090.331.15
Table 5. Comparison of nitrogen and phosphorus inputs and outputs for farmland, livestock, households, treatment facilities, and Japan as a whole.
Table 5. Comparison of nitrogen and phosphorus inputs and outputs for farmland, livestock, households, treatment facilities, and Japan as a whole.
103 t/Year
Nitrogen
InputOutput
Farmland4-2Chemical fertilizers354.92-2Domestic food223.8
4-3Circulated fertilizers255.33-2Domestic feed314.9
9BNF86.78Residuals102.6
10-1Deposition64.011-1DN81.9
Input Total760.9Output Total723.2
Livestock3-1Imported feed180.22-3Domestic livestock181.8
3-2Domestic feed314.94-5Circulated fertilizers212.8
3-3Circulated feed61.511-4Livestock excreta DN212.8
13-2Non-circulated waste97.4
Input Total556.7Output Total704.8
Households2-5Net food539.86-1Wastewater595.1
and Industry2-6Food for processing221.06-2Wastes163.8
Input Total760.8Output Total758.9
Treatment6-1Wastewater595.17-1Treated water197.3
Facilities6-2Wastes163.84-3Circulated fertilizer255.3
6-3Livestock excreta523.63-3Circulated feed61.5
13Non-circulated waste164.4
11-3Sewage DN257.3
11-5Incineration DN63.5
11-4Livestock excreta DN212.8
Input Total1282.5Output Total1212.3
Japan2-1Imported food380.55Export137.0
3-1Imported feed180.212Watershed417.3
4-1Imported fertilizers273.813Non-circulated waste164.4
9BNF86.711DN615.6
10Deposition(Land)556.0
Input Total1477.1Output Total1334.3
103 t/year
Phosphorus
InputOutput
Farmland4-2Chemical fertilizers140.62-2Domestic food43.1
4-3Circulated fertilizers119.03-2Domestic feed58.1
8Residuals13.1
Input Total259.6Output Total114.4
Livestock3-1Imported feed42.92-3Domestic livestock15.0
3-2Domestic feed58.14-5Circulated fertilizers83.4
3-3Circulated feed17.3
13-2Non-circulated waste19.1
Input Total118.2Output Total117.5
Households2-5Net food70.36-1Wastewater70.6
and Industry2-6Food for processing27.76-2Wastes45.9
Input Total98.0Output Total116.6
Treatment6-1Wastewater70.67-1Treated water15.4
Facilities6-2Wastes45.94-3Circulated fertilizer119.0
6-3Livestock excreta102.63-3Circulated feed17.3
13Non-circulated waste71.0
Input Total219.2Output Total222.6
Japan2-1Imported food27.15Export5.2
3-1Imported feed42.912Watershed28.2
4-1Imported fertilizers122.213Non-circulated waste71.0
Input Total192.2Output Total104.4
Table 6. Absolute value of output variance against input from input/output comparison in Table 5.
Table 6. Absolute value of output variance against input from input/output comparison in Table 5.
Output Variance Against Input
NitrogenPhosphorus
Farmland5%56%
Livestock27%1%
Households and Industry0%19%
Treatment Facilities5%2%
Japan10%46%
Table 7. Examination of calculation error in the food supply value from previous studies.
Table 7. Examination of calculation error in the food supply value from previous studies.
Nitrogen
YearNo. of StudiesStudiesCoefficient Value
19823B, C, I24%
19873B, C, I23%
19926B, C, D, E, F, I18%
19973C, D, I16%
20023D, I, K18%
20053H, J, K14%
20073D, I, K21%
20112J, K9%
20152J, K9%
Phosphorus
YearNo. of StudiesStudiesCoefficient Value
19922E, I39%
20022L, I46%
All studies state that “Food Balance Sheet” and “Standard Tables of Food Composition in Japan” have been referred, a methodology likewise adopted in this study.
Table 8. The details of each scenario.
Table 8. The details of each scenario.
ScenarioDescriptionUnchanged ItemsManipulated ItemsResulting Items
Control----
AReduction in chemical fertilizer useFertilizer supply (4-6)
Food supply (2-7)		Chemical fertilizers (4-2)⇩,
Circulated fertilizers (4-3)⇧		Imported fertilizers (4-1),
Non-circulated waste (13),
Circulated waste
B-1Expansion of organic farmland area (same yield)Fertilizer supply (4-6)
Food supply (2-7)		Chemical fertilizers (4-2)⇩,
Circulated fertilizers (4-3)⇧		Imported fertilizers (4-1),
Non-circulated waste (13), Circulated waste
B-2Expansion of organic farmland area (yield decrease)Food supply (2-7)Chemical fertilizers (4-2)⇩,
Circulated fertilizers (4-3)⇧		Imported fertilizers (4-1),
Non-circulated waste (13), Circulated waste
C-1Increased food self-sufficiency (current
dietary patterns)		Food supply (2-7)
Food composition in 2021		Imported food (2-1)⇩,
Domestic food (2-2)⇧,
Domestic feed (3-2)⇧		Circulated fertilizers (4-3), Fertilizer supply (4-6), Feed supply (3-4),
Livestock excreta (6-3), Non-circulated waste (13),
Circulated waste,
Residuals (8), BNF (9), DN (10-1), farmland area
C-2Increase in food self-sufficiency (shifted
dietary patterns)		Food supply (2-7)
Calorie consumption per capita		Imported food (2-1)⇩,
Domestic food (2-2)⇧		Circulated fertilizers (4-3), Fertilizer supply (4-6), Non-circulated waste (13), Circulated waste,
Residuals (8), BNF (9), DN (10-1), farmland area
Scenarios A~C reflect population decline by 17% in 2050, and all items were deducted by 17%. “⇧”indicates an increase in the item, and “⇩”indicates a decrease in the item.
Table 9. Input and output circulation ratios for each scenario.
Table 9. Input and output circulation ratios for each scenario.
Input Circulation RatioOutput Circulation Ratio
NitrogenPhosphorusNitrogenPhosphorus
Control28%41%25%62%
A33%49%29%72%
B-138%55%33%81%
B-238%54%35%86%
C-145%58%40%93%
C-233%48%28%75%
Table 10. The number of measured samples within and above the tolerance range of heavy metal regulation for fertilizer quality.
Table 10. The number of measured samples within and above the tolerance range of heavy metal regulation for fertilizer quality.
Dehydrated or Other Type of SludgeIncinerated Sludge Ash
Total no. of samples600194
No. of samples below 50% tolerance55514
No. of samples within 50–100% tolerance29153
No. of samples above 100% tolerance1641
Heavy metalTolerance value (mg/kg)
As50-10
Cd565
Hg212
Ni300322
Cr50061
Pb100-13
Tolerance value is established in “Act on the Quality Control of Fertilizer” [71].
Table 11. Current chemical fertilizer demand versus potential nutrient recovery from circulated sources (103 t/year).
Table 11. Current chemical fertilizer demand versus potential nutrient recovery from circulated sources (103 t/year).
103 t/Year
NitrogenPhosphorus
Current demand for chemical fertilizers354.9140.6
Potential circulated fertilizers249.0112.2
Non-circulated sewage sludge67.134.1
Food wastes *81.945.9
Non-circulated livestock excreta *48.719.1
Residuals *51.313.1
* N loss ratio due to compost is determined as 0.5 [55].
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Ushiyama, K.; Takano, M. Scenario Analysis of Japan’s Food and Feed Systems: Integrating Nutrient Flows with Sustainable Agricultural Policy. Sustainability 2026, 18, 5710. https://doi.org/10.3390/su18115710

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Ushiyama K, Takano M. Scenario Analysis of Japan’s Food and Feed Systems: Integrating Nutrient Flows with Sustainable Agricultural Policy. Sustainability. 2026; 18(11):5710. https://doi.org/10.3390/su18115710

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Ushiyama, Kimiko, and Masao Takano. 2026. "Scenario Analysis of Japan’s Food and Feed Systems: Integrating Nutrient Flows with Sustainable Agricultural Policy" Sustainability 18, no. 11: 5710. https://doi.org/10.3390/su18115710

APA Style

Ushiyama, K., & Takano, M. (2026). Scenario Analysis of Japan’s Food and Feed Systems: Integrating Nutrient Flows with Sustainable Agricultural Policy. Sustainability, 18(11), 5710. https://doi.org/10.3390/su18115710

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