N2N regional circular agriculture model in China: A case study of Luofang biogas project

Abstract

As China’s economy continues to expand rapidly, the agriculture sector is encountering increasing resource constraints and environmental challenge. Conventional agricultural practices are characterized by low rates of material and energy use, excessive resource consumption, and high pollutant emissions. However, circular agriculture is a promising new model for agricultural development that is sustainable, cost-effective, and environmentally friendly. This study presented the N2N regional circular agriculture model for the utilization of agricultural livestock and poultry waste in China based on feedback structure analysis theory and cost-benefit analysis (CBA), using the Luofang biogas project in Xinyu, Jiangxi province, operated by the Zhenghe Company as an example. The model improves resource utilization but also generates economic benefits for the biogas production enterprises. The results indicated that the sustainable operation of the N2N regional circular agriculture model can achieve multilevel resource utilization, improve the ecological environment, and generate substantial social, economic, and ecological benefits. The paper also discusses the importance of encouraging farmers to use biogas fertilizers and the role of economic incentives in promoting waste treatment and utilization.

Keywords:

• Agriculture production system
• circular model
• biogas project
• cost-benefit analysis
• sensitivity analysis
• sustainability
• renewable energy policy

1. Introduction

According to statistics released by the Chinese Ministry of Agriculture, the number of pigs bred in China has exceeded 700 million in recent years. However, with the consolidation of the breeding industry and the lack of adequate manure treatment facilities on farms, the concerns regarding pollution caused by large-scale livestock and poultry farming have become more severe (Abubaker et al., 2012). In addition, environmental protection issues have made it challenging for aquaculture businesses to expand their agricultural operations, and may even have contributed to the decline of the breeding sector. At the same time, the overemphasis on production in the crop industry has resulted in the excessive use of chemical fertilizers and pesticides, leading to a deterioration in the quality of agricultural products (Crosson & Rosenberg, 1989), soil compaction, ecological damage, and a decline in the overall value of agricultural cultivation (Wang, 2014). Therefore, the current problem is how to solve the two major issues of comprehensive manure utilization and chemical fertilizer abuse.

Recycling Agriculture is a highly beneficial model that not only provides significant environmental and social advantages, but also generates substantial economic benefits (Fan et al., 2018; Liwarska-Bizukojc et al., 2009). This model advocates for resource conservation and recycling using the 3 R principle of “reduce, reuse, recycle.” One of the most effective strategies for the treatment of pig manure is the biogas-tied planting and breeding integrated agricultural cycle model (Granlund et al., 2015; Hijazi et al., 2016). This model adopts multi-layer biomass energy recycling to efficiently control biogas slurry and accomplish ecological sewage discharge, take Germany as an example, which leads the world in the biogas industry, there are approximately 9000 biogas plants as biogas is believed to be crucial for agriculture (Grando et al., 2017). However, there is still significant room for improvement (Appel et al., 2016; Britz & Delzeit, 2013; Poeschl et al., 2010). Sweden, for example, advocates for the use of solely natural fertilizers such as animal and poultry manure instead of chemical fertilizers, herbicides, and insecticides in crop production (Hukari et al., 2016). In developed European and North American nations, statistics show that crop yield depends 70 to 80 percent on soil fundamental fertility and 20 to 30 percent on fertilizer. The utilization rate of manure nitrogen in Denmark has increased from 20% in 1980 to 45% in 2017 (Appel et al., 2016; Hijazi et al., 2016). Japan is promoting the development of farmers’ recycling awareness through various means to reduce the discharge of agricultural and animal husbandry wastes; economic incentives such as taxation, credit, incentives, and preferential treatment are implemented to promote the policy of “protection and cultivation of green resources”; and agricultural management organizations are being reformed to ensure that all aspects of agriculture are moving toward large-scale production.

2. N2N regional circular biogas project

The Chinese government has prioritized the development of biogas as a renewable energy source, as evidenced by its renewable energy policy (Mingxue Gao et al., 2019). This has resulted in the emergence of several successful recycling agriculture models across the country, which serve as valuable examples for others to follow. These models include the “pig-marsh-fruit (vegetable, tea)” model, the “pig (livestock and poultry)-marsh-earthworm-fruit” model, the agriculture and animal husbandry integrated cattle (sheep) model, the “fruit-grass-poultry” model, and the rice-duck (fish, shrimp, crab) symbiosis model (L. Chen et al., 2017). From the perspective of business entities, there are mainly three aspects: First, the ecological cycle mode represented by family farms, such as the small-scale ecological farming model of Shanghai Li Chunfeng Family Farm, which uses anaerobic fermentation of manure and consumes the resulting biogas residue through free farmland, achieving zero emissions for the farm. Second, the ecological agriculture cycle mode implemented by large-scale animal husbandry enterprises with large-scale biogas projects as the core, such as the green cycle industry chain constructed by leading livestock enterprises like Yili Group, which effectively solves the pollution of animal husbandry and the fertilizer problem of agricultural planting, achieving a “double improvement” in the efficiency of animal husbandry and planting. Third, the third-party centralized processing ecological cycle mode centered on counties, such as the N2N regional circular agriculture model invested and built by Jiangxi Zhenghe Group in Luofang Town, Chishui District. This model utilizes agricultural waste treatment centers and organic fertilizer centers to comprehensively collect and process the manure and dead pigs generated by “N” upstream breeding enterprises and connects “N” downstream planting zones to construct a regional green ecological cycle agricultural model. The Chinese government’s efforts to increase (Yu et al., 2008) the number of digesters have not fully addressed the issues of idleness and waste in rural household biogas (Y. Chen et al., 2010), despite a rapid increase in their installation. These problems are attributed to several factors, including the high barriers for biogas power generation (Gao et al., 2011; Guan et al., 2015; Hengeveld et al., 2016) and the lack of subsidies for organic fertilizers, technical support, and enforcement of environmental laws. Survey results reveal that only a meager 20 percent of large-scale farms have effectively combined planting and breeding, and most ecological recycling enterprises only involve the agricultural planting sector.

To address this, the N2N regional ecological circular agriculture model integrates the livestock and poultry breeding business into the industrial chain to resolve environmental protection issues in the aquaculture industry and generate economic benefits for businesses. To investigate the viability of this model, this article employed an economic management level approach, integrating economic benefits analysis, cost analysis, and financial analysis under various scenarios.

The N2N regional circular agriculture model (here in after referred to as the “N2N model”, as shown in Figure 1) is a transformative upgrade from the traditional “pig (cow, sheep)—biogas - fruit (vegetables, rice)” model. This model takes the county as the boundary and third-party centralized processing as the core, with the upper connection of N livestock and poultry breeding industries and the lower connection of N planting industries, to establish a regional balance between planting and breeding, and to promote the seamless connection of the surrounding breeding and planting industry chains, achieving the goal of “reduction, circulation, and regeneration” and promoting the development of regional ecological circular agriculture industry in the county. The model has been widely promoted in Yushui District, Dingshan County, and Jinxiang County of Jiangxi Province, as well as in Henan, Hainan, Guizhou, Inner Mongolia, Sichuan, and other provinces.

Figure 1. Flow chart of N2N circular agriculture model.

The “N2N model” is a closed-loop agricultural regional circular system in the county. The first “N” refers to the breeding industry subsystem, representing N breeding enterprises in the region; “2” refers to the processing center, representing agricultural waste resource utilization centers and organic fertilizer processing centers built by third-party enterprises; the second “N” refers to the planting industry subsystem in the region, representing N agricultural enterprises, planting households, and cooperatives. This model uses the core of the two-resource recycling and conversion centers to combine the upstream waste production end of the planting and breeding industries with the downstream resource regeneration product application end, promoting the seamless connection of various industry chains of breeding and planting in the region and achieving the goal of developing regional ecological circular agriculture in an integrated manner.

The main body of animal husbandry can effectively solve the non-point source pollution caused by manure and dead animals, reduce pollution costs, and lower the total production cost. At the same time, it can provide the required raw materials for the agricultural waste resource utilization center. The agricultural waste resource utilization center crushes and thermally disinfects the raw materials and produces waste residue through biological degradation. The waste residue is used as biogas fermentation material for biogas power generation and centralized gas supply to obtain profits, enabling residents to use clean energy, reduce living costs, and provide slurry and manure for the organic fertilizer processing center. Multi-level utilization of material energy and technology for organic waste transformation and regeneration. That is, using the principles of the ecological food chain, a new food chain is formed by adding cycles to the existing one, allowing material energy to be repeatedly transformed and utilized by different organisms in the food chain, resulting in a zero-waste production system. The organic fertilizer processing center produces organic fertilizer by processing slurry and manure, which is then sold to customers such as planting entities and ecological agriculture parks for profits. The planting entities can produce high-quality organic agricultural products through green production after obtaining organic fertilizer, increase planting income, reduce soil compaction, and achieve sustainable development. In addition, planting entities can also centrally and harmlessly process straw, rotten vegetable leaves, and rotten fruit through the agricultural waste resource utilization center, ensuring that each related entity in the N2N model can receive reasonable benefit allocation.

3. Material collection and research methods

3.1. Data collection

In 2016, Jiangxi Zhenghe Environmental Protection Engineering Co. Ltd invested $14.3 million in a large-scale biogas power production plant located in Luofang Town, Yushui District, Xinyu City through a PPP project. The plant boasts a CSTR anaerobic fermentation tank with a total volume of 27,000 m³, which enables the annual processing of 200,000 tons of waste and production of 9.12 million m³ of biogas. The generated biogas is mainly utilized for power generation and grid connection. Additionally, the plant produces 28,000 tons of biogas residual fertilizer and 150,000 tons of biogas fertilizer on an annual basis. Table 1 listed a detailed account of the technical and economic parameters of the biogas plant.

Table 1. Comprehensive technical and economic indicators of biogas engineering

index	numerical value	units
CSTR	27,000	m^3
Design organic waste treatment scale	200,000	t·a−1
Biogas	9.12	Million m^3·a−1
Biogas residue organic fertilizer	28,000	t·a−1
Biogas slurry organic fertilizer	150,000	t·a−1
Factory site area	127040	m^2
Factory building area	33048	m^2
The number of major equipment	130	sets
All staff	45	persons
Total investment	14.3	$ millions
Financial matching funds	5	$ millions
Local support	2.15	$ millions
Self-raised funds	7.15	$ millions

3.2. Methods

The present study employs a cost-benefit analysis (CBA) as a quantitative measure to assess the reduction of pollutant emissions. Furthermore, a sensitivity analysis is conducted to evaluate the influence of changes in three variables, namely biomass grid-connected power generation subsidies, biogas slurry prices, and biogas raw material prices, on the earnings generated by the biogas project. The research involves three main aspects:

1. Calculation of the ratios between revenue and expenses, which was approved by the principal of Zhenghe Company.

2. Evaluation of the regional circular economy of the N2N model through a field survey and frame diagram.

3. Based on the Chinese biogas growth scenario and the thirteenth Five-Year Plan’s greenhouse gas emission requirements, a new comprehensive development model for Chinese biogas is designed.

4. Results and analysis

In the proposed model, a centralized processing center is established to collect animal and poultry waste from eligible businesses, which is then fermented to produce biogas and organic fertilizer. Solid-liquid separation of biogas slurry generates biogas residue, which can be utilized as pollution-free organic or compound fertilizer following extensive processing. By relying on the services provided by Zhenghe Company for manure disposal, agricultural firms can reduce their investment and operating costs for environmental protection facilities, while maximizing market resource allocation and environmental benefits. The farms play a dual role as both consumers and suppliers of raw materials for power generation, allowing farmers to concentrate on agricultural output. This integrated approach contributes to a circular economic system, which creates multiple benefits in terms of economic, environmental, and social impacts (Guan et al., 2014).

4.1. Economic advantages evaluation

4.1.1. Biogas supply and energy production

The present study reports on the utilization of biogas produced from a facility in Luofang Town for two primary purposes: supplying energy to the town and generating energy for other uses. The government has effectively constructed a gas supply pipeline, whereby a portion of the biogas generated from the facility is utilized to power the homes of 6,000 individuals in the town and surrounding villages. The average daily gas consumption of these 6,000 families is approximately 1,200 m³, translating to an annual gas consumption of 438,000 m³. The selling price of biogas is $0.367 per cubic meter, yielding a total revenue of $0.16 million from centralized gas supply. The following is the formulation:

1200 × 0.367 × 365/10,000 = 0.16 ($ millions)

The utilization of biogas for power production and grid connection is the primary use for the remaining fraction. In Jiangxi Province, a purchase price of $0.098 per kilowatt-hour for biogas-generated electricity, which includes subsidies for power generation, has been endorsed by the approved policy (Xiaoli et al., 2018).

The project’s generator set comprises two 1.5 MW biogas generators, and each biogas unit has a generating capacity of 2.2 kW per cubic meter. It is necessary to undertake interim maintenance every 30–40 days, with a unit maintenance time of approximately 5–7 days, in accordance with biogas power generation’s safety production standards and empirical data. The generator set operates for around 20 hours every day, with an annual running time of approximately 6,000 hours, resulting in an annual power generation output of roughly 18 million kilowatts and an annual revenue of $1.764 million from power generation. The following is the formulation:

0.098 × 3,000 × 6,000/1,000,000 = 1.764 ($ millions)

4.1.2. Organic fertilizer revenue

In the study, it was found that biogas slurry and biogas residue, which are byproducts of organic fertilizer (Abubaker et al., 2012), can be obtained from 200,000 tons of manure produced annually by 400,000 pigs. Specifically, 0.14 tons of biogas residue and 0.75 tons of biogas slurry can be generated per ton of manure, resulting in an annual production of 28,000 tons of solid organic fertilizer and 150,000 tons of biogas slurry. To calculate the revenue generated from the solid organic fertilizer, considering the current market price of $100 per ton, the total income amounts to $2.8 million. The following is the formulation:

28,000 × 100/1,000,000 = 2.8 ($ millions)

However, the disposal of large quantities of biogas slurry poses a significant challenge to the industry. To address this issue, two handling techniques were identified. The first technique involves the use of membrane concentration and separation technology to separate the biogas slurry into high-concentration liquid fertilizer and emission-compliant recycled water. The second technique involves transporting the biogas slurry to orchard and vegetable bases. The corporation can earn $0.25 million annually from the sale of biogas slurry at the current price of $1.67 per ton. The following is the formulation:

150,000 × 1.67/1,000,000 = 0.25 ($ millions)

4.1.3. Pigs die from disease disposal subsidy

In compliance with the government’s subsidy policy, the company has implemented a harmless treatment policy for deceased pigs in the breeding chain at a subsidy rate of $13.33 per head, resulting in approximately 20,000 pigs being treated per annum due to disease. Following the deduction of the feeding cost of $1.67 per head, the overall contribution of this initiative amounts to $0.23 million in revenue. The formula is:

(13.33–1.67) ×20,000/1,000,000 = 0.23 ($ millions)

4.1.4. Carbon trading revenues (currently earn no revenue)

Additionally, the company’s carbon trading revenues presently remain nonexistent. The proposed revenue per cubic meter of biogas from carbon trading is $0.08, while the CO₂ equivalent of methane is 25 times greater than that of carbon dioxide. Upon the approval of the carbon trading proposal, the company anticipates a yearly increase in revenue of $0.78 million. The formula is:

27,000 × 365 × 0.08/1,000,000 = 0.78 ($ millions)

The application process for Clean Development Mechanism (CDM) projects is hindered by a number of complexities, including the lack of a neutral third-party review agency, the inconsistent quality of project consulting organizations, and the uncertain property rights associated with carbon sinks (Y. Chen et al., 2017; Gangnibo et al., 2010; Rahman et al., 2018). These factors contribute to the difficulties of navigating the CDM project application process. And, as CDM requires third-party assessment, no gains are currently being made.

4.1.5. Manure treatment fee

In the context of the “who pollutes, who pays, who governs, who benefits” premise, a third-party management organization currently charges aquaculture businesses $1.67 per ton of pollution control fees for up to 30 axioms. Assuming this organization handles 200,000 tons of manure annually, the annual cost of manure treatment would amount to $0.334 million. The following is the formulation:

200,000 × 1.67/1,000,000 = 0.334 ($ millions)

4.2. Cost analysis

As the entire biogas project is subject to contractual agreements for each phase of production, the majority of engineering operating expenditures are comprised of various expenses such as transportation, power generation, solid organic fertilizer production, fixed asset depreciation, management fees, and finance fees.

4.2.1. Transportation cost

The range for raw material collection is limited to a maximum of 30 kilometers from the biogas station, with an average transportation distance of 15 kilometers per vehicle, as based on the current operational scenario. In the event that a manufacturer transports 1000 tons of material per day at a rate of $2.5 per ton, their yearly transportation expenses would amount to $0.9125 million. The formulas for calculation are as follows:

1000 × 2.5 × 365/10,000 = 0.9125 ($ millions)

4.2.2. Cost of power generation

The outsourcing service cost is $0.01/kW•h, while biological desulfurization costs $0.003/kW•h and self-consumption power costs $0.015/kW•h. Therefore, the total cost of power generation amounts to $0.028 per kW•h. Consequently, the annual cost of power generation for the biogas project is $0.51 million. The formulas for calculation are as follows:

0.028 × 3,000 × 6,000/1,000,000 = 0.51 ($ millions)

4.2.3. Cost of organic solid fertilizer production

The estimated cost of producing each ton of organic fertilizer is approximately $70, with the primary expenses including $19 for production auxiliary materials, $3 for biological microbe, $5 for production power, $10 for packaging fees, $23 for manufacturing, and $10 for shipping. Based on these expenses, the total annual cost of producing solid organic fertilizer is calculated to be $1.96 million. This formulation presents as follows:

28,000 × 70/1,000,000 = 1.96 ($ millions)

4.2.4. Decay of immovable assets

The total investment for this project amounts to $14.3 million. Using the composite life depreciation method, the annual depreciation of fixed assets that are 20 years old, assuming a 5 percent residual value, is calculated to be $0.68 million. The formulation presents as follows:

14.3 × (1–5 percent)/20 = 0.68 ($ millions)

4.2.5. Management fees

The project is equipped with a staff of 45 full-time employees responsible for the operation and management of maintenance systems, comprising 2 individuals in the financial department, outsourced personnel for the power generation department, 6 employees in the comprehensive department, 15 employees in the raw materials department, 15 employees in the organic fertilizer production department, 2 employees in the safety production department, and 5 administrative staff. Based on an assumed annual income of $10,000 per capita, the annual salaries for the staff are estimated to be $0.45 million.

4.2.6. Financial costs

Furthermore, given the $7.155 million self-raised funds for the project, the financial cost is approximately $0.43 million per annum, assuming an approximate interest rate of 6%. The formulation presents as follows:

7.155 × 6 percent = 0.43 ($ millions)

The project’s profits can be computed as $1.008 million annually, based on the income and expenses outlined above. The details of these calculations are presented in Table 2.

Table 2. Production cost and earnings of biogas project (millions US dollars)

Cost item		Cost	Revenue item	Revenue
Variable costs	Transportation	0.5	Centralized gas supply	0.16
	Electricity	0.51	Biogas power generation	1.764
	Organic fertilizer	1.96	Organic fertilizer	2.8
Fixed costs	Fixed assets depreciation	0.68	Biogas slurry	0.25
	Management expenses	0.45	dead pig treatment subsidy	0.23
	Finance charges	0.43	CDM	0
			wastes handling fees	0.334
	total	4.53	total	5.538
	profit	1.008

4.3. Financial analysis under different scenarios

The previous calculations reveal that the project’s typical operational profit amounts to $1.008 million, not taking into account any environmental or social benefits. Sensitivity analysis was conducted using three variables: biomass grid-connected power prices, biogas slurry prices, and biogas raw material prices, to ascertain the effects on earnings of the biogas project when the variable values undergo changes. This procedure served to provide further confirmation of the influence of control variables on the revenue generated by the biogas project, as explored in the preceding section.

4.3.1. Cost of power

Based on the Jiangxi Provincial Development and Reform Commission’s approved on-grid tariff of $0.098/kW•h, the biogas power generation project generates an annual revenue of $1.764 million, which accounts for 1.85% of the total revenue. However, the company lacks autonomy in determining energy prices, and any future changes in the pricing system established by the NDRC may significantly impact the company’s performance. Table 3 illustrates that the company’s earnings would experience a decline from $2.844 million to $0.144 million if the on-grid rate were reduced from $0.02/kW•h to $0.05/kW•h. This highlights the importance of closely monitoring any potential changes to the on-grid rate in order to make informed business decisions.

Table 3. The sensitivity analysis of the engineering efficiency of the power price fluctuation

power price/$	0.2	0.15	0.125	0.1	0.075	0.05
Total revenue/$ million	7.374	6.474	6.024	5.574	5.124	4.674
profits/$ million	2.844	1.944	1.494	1.044	0.594	0.144

4.3.2. Costs of biogas slurry

According to Table 4, the revenue derived from biogas slurry sales amounted to $0.25 million, constituting 4.51% of the total revenue. A decrease in biogas slurry prices from $5/t to -$5/t is shown to cause a decrease in the enterprise’s total revenue from $6.058 million to $4.558 million and a decrease in profit from $1.528 million to $0.028 million. Hence, the price of biogas slurry directly affects the company’s profitability (Yazan et al., 2018). Specifically, a price of $50 per ton can result in a profit of $0.778.

Table 4. The sensitivity analysis of the engineering efficiency of biogas slurry price fluctuation

Biogas slurry price/$	5	3	1	0	−1	−3	−5
Total revenue/$ million	6.058	5.758	5.458	5.308	5.158	4.858	4.558
profits/$ million	1.528	1.228	0.928	0.778	0.628	0.328	0.028

4.3.3. Costs of raw materials

The production of biogas necessitates solely two primary constituents: the partner’s livestock excrement and rice straw from the surrounding agricultural area. Table 5 illustrates that an escalation in the procurement expense of livestock excrement from the current -$5/ton to $5/ton would lead to a surge in the company’s overall revenue from $6.204 million to $4.204 million. Nonetheless, the company’s net earnings would plummet from $1.674 million to -$0.326 million, indicating a $1.674 million contraction. It follows that the cost of acquiring raw materials assumes a pivotal role in determining the feasibility of biogas plants, assuming that all other parameters remain constant.

Table 5. The sensitivity analysis of the engineering efficiency of raw material price fluctuation

Manure collection cost/$	−5	−3	−1	0	1	3	5
Total revenue/$ million	6.204	5.804	5.404	5.204	5.004	4.604	4.204
profits/$ million	1.674	1.274	0.874	0.674	0.474	0.074	−0.326

5. Conclusions and recommendations

5.1. Conclusions

The present study applies an economic benefit analysis and a sensitivity analysis to investigate the the N2N regional ecological circular agriculture model’s biogas project in Yushui District, Xinyu City, Jiangxi Province.

This model mainly achieves multi-level recycling of agricultural waste by using the waste from one industry as raw materials for the next industry, such as straw, animal manure, etc. It aims to achieve fertilizer, energy, feed, and reprocessing of agricultural waste, ultimately achieving zero emissions. It includes three specific modes: comprehensive utilization of straw, comprehensive utilization of livestock and poultry manure, and comprehensive utilization of biogas. County-integrated ecological recycling agriculture is a new model of agriculture that aims to achieve ecological recycling, resource sharing and synergistic development to meet people’s demand for high-quality, healthy, and sustainable agricultural products. It does this by organically combining the agriculture, animal husbandry, aquaculture, and forestry industries to form a recycling ecosystem that maximises the use of resources and achieves sustainable economic, social and environmental development.

The main features of integrated eco-cycle agriculture in the county include the following:

1. Taking ecological recycling as the core. County-integrated ecological cycle agriculture is based on natural ecological cycles, using the interaction of plants, animals, microorganisms, and other ecosystems to form an ecological cycle system to maximise the use of resources and the self-healing of the ecosystem.

2. Based on resource sharing. County-integrated ecological cycle agriculture organically combines agriculture, animal husbandry, aquaculture, and forestry industries to achieve resource sharing and synergistic development and improve resource utilisation efficiency and economic benefits.

3. Supported by scientific and technological innovation. County-integrated ecological recycling agriculture uses advanced technological means and management models, such as precision agriculture, intelligent management, and biotechnology, to improve production efficiency and product quality, while protecting the ecological environment and achieving sustainable economic, social and environmental development.

4. Market-oriented. County-integrated ecological recycling agriculture attaches importance to market demand and consumers’ health needs, focuses on product quality, safety, and environmental protection, develops special agricultural products, promotes brands and increases the added value of products and market competitiveness.

The practice of county-integrated ecological recycling agriculture has proved that it can effectively improve the overall efficiency and sustainable development of agriculture, promote increased farmers’ income and rural economic development, while protecting the ecological environment and ecological resources and contributing to the realization of rural revitalization and the construction of beautiful villages.

5.2. Recommendations

The N2N regional ecological circular agriculture model represents an innovative model to resource conservation and recycling. The results demonstrate that the N2N regional circular agriculture model is capable of generating positive economic, social, and ecological benefits when the utilization rate of biogas project by-products (i.e., biogas, biogas slurry, and biogas residue) reaches 100% and suggests its potential for model, replicable, and generalizable performance. Specifically, the biogas production enterprise plays a critical role in addressing waste pollution associated with large-scale livestock and poultry farming. By supplying growers with organic fertilizer and household energy, the enterprise enhances planting efficiency (Li et al., 2012) and improves living standards.

Based on research findings, the present study offers several recommendations for the adoption of sustainable and environmentally friendly agricultural practices:

(1) The government should implement a subsidy scheme to incentivize the use of biogas-based organic fertilizers. This scheme should extend to businesses, rural cooperatives, family farms, and peasant families, thereby establishing a conducive policy environment for the successful implementation (Herrmann et al., 2017) of the N2N regional ecological circular agriculture model.

(2) Introducing a policy of growing ryegrass on fallow fields throughout the winter can significantly improve environmental protection and the problem of inadequate feed in the south. This policy can help absorb the methane slurry produced by the biogas project and promote the sustainable use of resources.

(3) It is recommended to plan agricultural planting demonstrations within the N2N model’s surrounding area. This can involve labeling agricultural products with “green” and “healthy” attributes, thereby enhancing product pricing and promoting the development of a pollution-free brand for regional agricultural products.

(4) Increasing the promotion of biogas slurry use can foster environmentally friendly agricultural production practices and enhance fertilizer awareness among farmers. To reduce the cost of using biogas slurry through fertilizing technology, leading social organizations can provide socialized services such as transportation.

(5) To foster a conducive market environment for third-party management of livestock and poultry manure, it is crucial for the livestock sector and environmental authorities to strengthen enforcement of environmental laws and regulations while also increasing the fees associated with waste and sewage discharge from breeding enterprises.

Acknowledgments

We appreciate the financial support from the China National Natural Science Foundation (No. 71263024, No.71663030).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Notes on contributors

Rao Han

Rao Han was born in Fuzhou City, Jiangxi Province, in December 1999. I am a student of Accounting at Jiangxi Agricultural University. My primary research areas are agricultural project investment appraisal and ecological circular agriculture.

Wang Huo-Gen

Wang Huo-Gen Born in Fuzhou City, Jiangxi Province, in July 1971. A tutor of Professional degree students in technical economy and management, and Accounting. Research directions include agricultural project investment evaluation, practical and economic theories such as ecological circular agriculture. With the goal of promoting the development of an agricultural ecological society, my team's primary project research focuses on the practical benefits of agricultural biogas engineering in China, combined with China's economic theory and policy.