Analysis of the Fertilizer and Energy Utilization Potential of Livestock and Poultry Manure Resources—A Case Study Concerning Liaoning Province, China

Abstract

The efficient resource utilization of livestock manure has received extensive attention worldwide at present, and the related resource utilization technology has been continuously improved, while the potential for the utilization of livestock manure in terms of fertilizer and energy is not yet clear. In order to more accurately assess the potential for fertilizing and energizing livestock manure, this study took Liaoning Province, a large livestock and poultry farming province in China, as an example. Based on statistical data and field research, this study assessed the potential for fertilizing and energizing livestock manure based on calculating the amount of livestock manure resources in Liaoning Province in 2023 by applying the method of excretion coefficients and other methods. The results show that (1) the total amount of livestock manure resources in Liaoning Province in 2023 was 104.41 × 10⁶ t; (2) the amounts of organic matter (OM), nitrogen (N), phosphorus (P), and potassium (K) that the livestock manure could be converted into were 18.86 × 10⁶ t, 2.03 × 10⁶ t, 3.05 × 10⁶ t, and 2.26 × 10⁶ t, respectively, which was sufficient to replace the total amount of chemical fertilizer application in Liaoning Province; and (3) the total energization of livestock manure in Liaoning Province could be converted into 3826.73 × 10⁴ t standard coal or 1950.61 × 10⁷ m³ biogas, respectively. The results of this study can provide a reference basis for the preliminary estimation of the potential of livestock manure resource utilization in China and even in the world, which is of great significance for the global reduction in the dependence on chemical fertilizers, the optimization of the energy structure, and the maintenance of the ecological balance. This can also help to promote the improvement of the policies related to the resource utilization of livestock manure to achieve the high efficiency of the resource utilization of livestock manure.

1. Introduction

Livestock and poultry farming, as an important part of the livestock industry, develops intensively and on a large scale, providing abundant meat, egg, and milk products for human life, and making important contributions to the sustainable development of the livestock industry and the global circular economy [1,2]. According to relevant media reports, the global livestock and poultry farming market size exceeded USD 1.5 trillion in 2023. China, as the world’s largest hog and poultry farming country, produced 96.41 × 10⁶ t, 41.97 × 10⁶ t, and 35.63 × 10⁶ t of meat, milk, and egg products, respectively, in 2023, of which meat production accounted for more than 30% of global meat production [3]. However, livestock manure, as the most important waste of livestock and poultry farming, is the direct excretion of livestock and poultry digestion and metabolism, and its quantity has increased dramatically with the large-scale development of livestock and poultry farming, which has brought many problems such as health hazards, greenhouse gas emissions, deterioration of water quality, and odors for the sustainable development of human beings and the environment [4,5,6]. In fact, livestock manure is a good renewable energy source, which can be used as agricultural fertilizer through fermentation [7], converted into usable energy sources such as biogas or electricity through anaerobic fermentation or combustion [8], or made into feed for secondary consumption by livestock through drying or fermentation [9]. Therefore, livestock manure is also known as “misplaced resources” [10]. However, there is still much room for improvement in the current global utilization rate of livestock manure resources [5]. As far as China is concerned, the current annual generation of livestock manure is about 4 billion tons, while the resource utilization rate is only 75% [11], and the resource utilization efficiency of livestock manure still needs to be further improved in order to give full play to its utilization value and to provide more comprehensive economic, social, and ecological benefits [12].

In the face of the coexistence of livestock manure pollution and the low resource utilization rate, and the urgent need to address this situation, the global community in recent years has paid great attention to the resource utilization of livestock manure. With energy and fertilizer being the main directions of livestock manure resource utilization, related research mainly focuses on these two aspects. Srivastava et al. explored new ways of sustainable energy and the fertilizer utilization of livestock manure worldwide and analyzed the environmental and economic benefits of different utilization methods [13]. Finzi et al. evaluated the technical, economic, and environmental performance of an integrated livestock manure energy and nutrient treatment system in Northern Italy through a 5-year study, which provided significant value for improving livestock manure utilization efficiency and reducing its impact on the environment [14]. China has also gradually recognized the necessity and significance of livestock and poultry waste resource utilization, and has issued a series of laws, regulations, and policy measures in recent years, such as the Opinions on Accelerating the Advancement of Livestock and Poultry Breeding Waste Resource Utilization and the Measures for the Examination of the Resource Utilization of Livestock and Poultry Breeding Waste. These laws, regulations, and policy measures stipulate the direction of the development of livestock and poultry waste resource utilization and its development objectives and related policies, and the Chinese government vigorously promotes comprehensive livestock manure resource utilization [15]. However, the current research mainly focuses on enhancing and improving specific technologies for the resource utilization of livestock manure to increase its resource utilization rate, while the resource utilization potential of livestock manure in terms of fertilizer and energy is still unclear. As a result, the actual economic and environmental feasibility of using livestock manure as a substitute for chemical fertilizers and fuels in the resource utilization process is in some doubt. Therefore, there is an urgent need to analyze the feasibility and potential of using livestock manure in fertilizer and energy applications, reveal the important value of its resource utilization, provide a decision-making basis for relevant policymakers, and effectively promote the efficient resource utilization of livestock and poultry wastes.

As a nationally important livestock product production and supply base, Liaoning Province in China has a well-developed animal husbandry industry on a large scale. It provides a large amount of meat, eggs, milk, and other livestock and poultry products for the entire Chinese market. In 2023, the total output value of the province’s livestock and poultry industry chain reached CNY 240 billion. This plays an important role in guaranteeing the supply of China’s livestock product market and stabilizing market prices [16]. Behind this significant economic and social contribution, Liaoning Province naturally faces the practical dilemma of high livestock manure production and the urgent need to improve resource utilization methods and efficiency [17,18]. Therefore, this study aims to reveal the economic, social, and ecological values of livestock manure resource utilization in Liaoning Province. It will comprehensively evaluate the actual utilization potentials of livestock manure in terms of fertilizer and energy, and analyze the economic benefits it can generate as an alternative to chemical fertilizers and other fertilizers during resource utilization. The results of this study will provide a reference for estimating the potential of livestock manure resource utilization across China and the world. They are of great significance for reducing dependence on chemical fertilizers, optimizing the energy structure, relieving environmental pressure, and maintaining ecological balance. At the same time, they will provide a decision-making basis for relevant policymakers and promote the continuous improvement of policies related to livestock manure resource utilization.

2. Research Methods and Data Sources

2.1. Overview of the Study Area and Data Sources

Liaoning Province is in the south of Northeast China, between 38°43′–43°26′ N and 118°53′–125°46′ E, which is the central area of the Northeast Economic Zone (Figure 1). Liaoning Province has a temperate continental monsoon climate with sufficient sunshine and abundant rainfall. The annual average temperature is 5.2–11.7 °C and the climate is mild, which is suitable for the development of animal husbandry in the farming industry. Liaoning Province is also the main livestock breeding area in Northeast China. Many types of animals are bred in this province. The main ones are pigs, cattle, sheep, and poultry. In 2023, 3.09 million cattle, 28.5 million pigs, 8.75 million sheep, and 1518.3 million poultry animals were bred in this province. The statistical data used in this study mainly came from the Liaoning Statistical Yearbook and the Liaoning Rural Statistical Yearbook, including data on the feed intake of livestock and poultry in 14 cities in Liaoning Province in 2023. According to the statistics on the types of livestock and poultry in the yearbook, pigs, cattle, sheep, and poultry were selected for analysis.

2.2. Method for Estimating Livestock Manure Production

The production of livestock manure (Y_manure) was calculated using Formula (1).

$$Y_{manure}={\displaystyle {\sum }_{i=1}^{n}Q{d}_i·T_i·e_i}$$

(1)

Y_manure denotes the production of livestock manure (10⁴ t); n denotes the number of species of livestock and poultry; Qdi denotes the total number of the i-th type of animal (livestock or poultry); Ti denotes the breeding period of the i-th animal (livestock or poultry) (d); and e_i denotes the pollution production coefficient of the i-th animal (livestock or poultry; kg·d⁻¹).

(1)

Pollution coefficient of livestock manure

The daily excretion coefficient of livestock manure is a commonly used parameter for estimating the production of livestock manure. The daily excretion coefficient of livestock and poultry is related to many factors, such as livestock and poultry species, body weight, growth stage, feed type, region, climate, and so on [19]. China carried out its first national pollution source census in 2008 and, subsequently, published the First National Pollution Source Survey Livestock and Poultry Breeding Industry Source Production and Discharge Coefficient Manual, which contained a more detailed collection of different regions, the different feeding statuses of the main types of livestock, and data on the poultry manure pollution coefficient and discharge coefficient. In this study, based on pollution production coefficient data concerning various livestock and poultry species in the northeast region mentioned in the manual cited above, the weighted average of the fecal volume coefficient was calculated according to the body weight index, serving as the reference coefficient used in the estimations in this study. The pollution coefficient for pig, beef cattle, dairy cattle, sheep, and poultry was 6.29 kg·d⁻¹, 22.67 kg·d⁻¹, 35.74 kg·d⁻¹, 2.6 kg·d⁻¹, and 0.1 kg·d⁻¹, respectively [20].

(2)

Livestock and poultry feeding cycles

The feeding cycle of livestock and poultry was determined according to average feeding cycles. The average feeding cycles for pigs, cattle and sheep, and poultry were 199 days, 365 days, and 210 days, respectively.

(3)

Number of livestock and poultry animals

The number of livestock and poultry animals bred in a region must be determined according to the respective animals’ feeding cycles. If the feeding cycle is less than one year, the number of slaughtered animals in this year already contains the number of slaughtered animals at the end of the previous year, so the number of slaughtered animals at the end of the year is taken as the number of livestock and poultry animals bred in this year. If the feeding cycle is more than one year, the quantity bred is the number of animals at end of the year. The breeding quantity data concerning the main livestock and poultry species in Liaoning Province mainly came from the Liaoning Statistical Yearbook. The quantities of livestock and poultry animals bred in Liaoning Province in 2023 are shown in

Table 1. The number of livestock and poultry animals bred in Liaoning Province.

Area	Pigs (104)	Beef Cattle (104)	Dairy Cattle (104)	Sheep (104)	Poultry (104)
Shenyang	403.54	58.54	14.64	69.07	8698.13
Dalian	219.48	12.59	3.15	40.32	28,295.78
Anshan	98.94	8.34	2.08	23.21	17,506.21
Fushun	33.75	4.74	1.19	23.06	2861.24
Benxi	54.92	5.45	1.37	20.91	2157.22
Dandong	47.22	4.52	1.14	23.29	9585.8
Jinzhou	460.89	20.79	5.19	72.61	11,706.22
Yingkou	20.33	3.28	0.83	59.36	8409.43
Fuxin	333.42	33.05	8.27	188.79	5653.51
Liaoyang	67.84	4.88	1.23	16.28	1584.95
Panjin	45.41	1.03	0.26	2.26	12,339.28
Tieling	334.79	34.53	8.64	29.84	19,200.17
Chaoyang	440.71	45.22	11.31	222.25	14,600.54
Huludao	285.25	10.81	2.71	83.63	9231.61
Total province	2846.49	247.77	62.01	874.88	151,830.09

.

2.3. Method for Estimating the Nutrient Content of Livestock Manure

Different types of livestock manure have different nutrient contents, and factors such as feeding methods, growth conditions, and food intake will affect the nutrient content of livestock manure. The nutrient content of organic matter (OM), nitrogen (N), phosphorus (P), and potassium (K) in livestock manure was calculated using the coefficient of livestock manure resources and nutrient content. The formula is shown below.

$$N_{manure}={\displaystyle {\sum }_{i=1}^n{Y}_{manure}·{\delta }_i}$$

(2)

N_manure denotes the nutrient content of livestock manure (10⁴ t); n denotes the number of species of livestock and poultry; Y_manure denotes the production of livestock manure (10⁴ t); and δ_i denotes the nutrient content coefficient of the i-th livestock or poultry animal (%).

When this study was conducted, there were no authoritative data on the determination of the main nutrient content coefficients of livestock manure in China, and the nutrient content coefficients adopted by scholars, with different disciplines and aims, are not all consistent. After reviewing numerous studies and research results, considering the scientific nature of the measurement method, 170 samples of livestock manure from 20 provinces in China were studied, and the contents of total nitrogen, total phosphorus, and total potassium in the samples were determined via distillation, vanadium molybdenum yellow colorimetry, and flame photometry, respectively [21]. The nutrient content coefficients of each type of livestock manure are shown in

Table 2. Nutrient content coefficient of the main types of livestock manure.

Type of Livestock Manure	OM (%)	N (%)	P2O5 (%)	K2O (%)
Pig manure	14.5	2.28	3.97	2.09
Cattle manure	16.5	1.56	1.49	1.96
Sheep manure	25.5	1.31	1.03	2.40
Poultry manure	21.5	2.08	3.53	2.38

Note: OM—organic matter, N—nitrogen, P₂O₅—phosphorus, and K₂O—potassium. The same notation is used in the following tables.

.

2.4. Livestock Manure Energy Calculation Method

Standard coal conversion and biogas conversion are usually used to evaluate the energy utilization potential of livestock manure [22]; that is, according to the energy conversion coefficient and gas production of different types of breeding waste, the breeding waste resources are converted into standard coal and biogas, and the energy contained in biomass is estimated through relevant parameters in order to measure its energy potential.

The standard coal calculation formula for the conversion of livestock manure is given below.

$$C=Y_{\mathrm{manure}}·R_i·X_i$$

(3)

i denotes the type of livestock manure, with i = 1, 2, 3…, n; Y_manure denotes the production of livestock manure (10⁴ t); R_i denotes the recoverable coefficient of the i-th type of livestock manure; and X_i denotes the standard coal conversion coefficient of the i-th type of livestock manure.

The formula for calculating the biogas production potential of livestock manure is given below.

$$G=Y_{manure}·R_i·V_i$$

(4)

i denotes the type of livestock manure, with i = 1, 2, 3…, n; Y_manure denotes the production of livestock manure (10⁴ t); R_i denotes the recoverable coefficient of the i-th type of livestock manure; and V_i denotes the unit biogas production of the i-th type of livestock manure.

Through a field investigation, it was found that the recoverable coefficient of pig manure was higher than that of the other types of manure, and it could basically be fully recovered, while the recoverable coefficients of the other types of manure were all only about 60%. After a comparison with other related documents, it was found that the data contained were basically consistent with the results of our field investigation [23,24,25]. This may be because pigs are usually kept in the intensive captive mode, and manures are often concentrated in closed or semi-closed septic tanks, convenient for mechanical or manual unified collection and treatment. Cattle and sheep are mostly grazing or semi-grazing animals, and their manures are scattered over pastures or in the wild, so it is difficult to collect them in one location. Although chickens are mostly kept in cages, their manure is often mixed with padding, for which the cost of separation is high. The parameters of the energy assessment of livestock manure were determined as shown in

Table 3. Energy parameters of livestock manure.

Type of Livestock Manure	Standard Coal Conversion Coefficient	Unit Biogas Production (m3·kg−1)	Recoverable Coefficient
Pig manure	0.43	0.2	1.0
Cattle manure	0.47	0.3	0.6
Sheep manure	0.53	0.3	0.6
Poultry manure	0.64	0.3	0.6

.

3. Results and Analysis

3.1. Livestock Manure Resources in Liaoning Province

Based on the statistical data on Liaoning Province in 2023, the total quantity of livestock manure resources in Liaoning Province was calculated according to Formula (1). The livestock manure resources and the proportions of different livestock manure resources in Liaoning Province in 2023 are shown in Figure 2.

The livestock manure resources in Liaoning Province in 2023 amounted to 104.41 × 10⁶ t. Pig manure amounted to 35.63 × 10⁶ t, accounting for 34.12% of the total, and pigs were the largest producers of livestock manure resources; cattle manure amounted to 28.59 × 10⁶ t, accounting for 27.39% of the total, and the manure resources of beef and dairy cattle amounted to 20.50 × 10⁶ t and 8.09 × 10⁶ t, respectively; sheep manure amounted to 8.30 × 10⁶ t, accounting for 7.95% of the total; and poultry manure amounted to 31.88 × 10⁶ t, accounting for 30.54% of the total.

The utilization of livestock manure resources was identified based on the livestock manure resources in each city. The regional distribution of livestock manure resources in Liaoning Province is shown in

Table 4. Livestock manure resources in each city in Liaoning Province.

Area	Pig Manure (104 t)	Cattle Manure (104 t)	Sheep Manure (104 t)	Poultry Manure (104 t)	Total (104 t)	Proportion (%)
Shenyang	505.12	675.37	65.55	182.66	1428.70	13.68
Dalian	274.73	145.27	38.26	594.21	1052.47	10.08
Anshan	123.84	96.14	22.03	367.63	609.64	5.84
Fushun	42.25	54.75	21.88	60.09	178.97	1.71
Benxi	68.74	62.97	19.84	45.30	196.85	1.89
Dandong	59.11	52.27	22.10	201.30	334.78	3.21
Jinzhou	576.90	239.73	68.91	245.83	1131.37	10.84
Yingkou	25.45	37.97	56.33	176.60	296.35	2.84
Fuxin	417.35	381.36	179.16	118.72	1096.59	10.50
Liaoyang	84.92	56.43	15.45	33.28	190.08	1.82
Panjin	56.84	11.91	2.14	259.12	330.01	3.16
Tieling	419.06	398.43	28.32	403.20	1249.01	11.96
Chaoyang	551.64	521.72	210.92	306.61	1590.89	15.24
Huludao	357.05	124.80	79.36	193.86	755.07	7.23

.

Due to the different development scales of the livestock and poultry industry in each city, the resources of livestock manure varied greatly. Chaoyang had the most livestock manure resources, reaching 15.91 × 10⁶ t, accounting for 15.24% of the total livestock manure resources in the province. The amount of manure in Shenyang, namely, 14.29 × 10⁶ t, was second only to that in Chaoyang and accounted for 13.68% of the total manure resources. Among all cities, Fushun had the least amount of livestock manure, amounting to only 1.79 × 10⁶ t, accounting for 1.71% of the total (Table 4). In the entire province, in terms of the manure resources produced by the different types of livestock and poultry, Jinzhou had the most pig manure, Shenyang had the most cattle manure, Chaoyang had the most sheep manure, and Dalian had the most poultry manure.

The different types of livestock manure resources in various cities in Liaoning Province as percentages of the total amount of manure resources in the city is shown in Figure 3. The percentages of the different types of livestock manure resources in each city with respect to the total amount of manure resources are not the same. In nine cities, pig and cattle manure resources account for more than half of their manure resources, while the remaining five cities’ poultry manure resources account for more than half of the total resources. The amount of sheep manure accounts for basically the smallest proportion of the total amount of livestock manure resources in each city, which may be related to the number of sheep bred.

3.2. Fertilizer Potential of Livestock Manure in Liaoning Province

3.2.1. Nutrient Content of Livestock Manure Resources in Liaoning Province

Based on the livestock manure resources in Liaoning Province in 2023, combined with the nutrient content coefficients of different livestock manures, the nutrient content of livestock manure resources could be calculated by using Formula (2). The results are shown in

Table 5. Nutrient content of livestock manure resources in Liaoning Province.

Type of Livestock Manure	OM (104 t)	N (104 t)	P2O5 (104 t)	K2O (104 t)
Pig manure	516.63	81.24	141.45	74.47
Cattle manure	471.75	44.60	42.60	56.04
Sheep manure	211.72	10.88	8.55	19.93
Poultry manure	685.51	66.32	112.55	75.88
Total	1885.61	203.04	305.15	226.32

.

In 2023, the OM content of livestock manure resources in Liaoning Province was about 18.86 × 10⁶ t, among which the OM content provided by poultry was the highest, reaching 6.86 × 10⁶ t. N content amounted to 2.03 × 10⁶ t, and pig manure amounted to 81.24 × 10⁴ t, accounting for about 40% of the total (Table 5). The P₂O₅ content was 3.05 × 10⁶ t, and pig manure accounted for the highest P₂O₅ content, 1.42 × 10⁶ t, followed by poultry manure. The K₂O content in poultry manure and pig was 75.88 × 10⁴ t and 74.47 × 10⁴ t, respectively, accounting for about 66% of the total.

Among the different types of livestock and poultry, the manure of pigs can provide the most nutrients, and the total nutrient content was 2.97 × 10⁶ t. The second most nutritious was poultry manure, which provided 2.55 × 10⁶ t. Furthermore, cattle manure contained 1.43 × 10⁶ t of nutrients. Sheep manure had the lowest nutrient content (Table 5).

Identifying the nutrient content of livestock manure resources in each city forms the basis for the use of livestock manure as fertilizer. The regional distribution of the nutrient content of livestock manure resources in Liaoning Province is shown in

Table 6. Nutrient content of livestock manure resources in each city in Liaoning Province.

Area	OM (104 t)	Proportion (%)	N (104 t)	Proportion (%)	P2O5 (104 t)	Proportion (%)	K2O (104 t)	Proportion (%)
Shenyang	240.66	12.76	26.71	13.16	37.24	12.20	29.71	13.13
Dalian	201.32	10.68	21.39	10.54	34.44	11.29	23.65	10.45
Anshan	118.48	6.28	12.26	6.04	19.55	6.41	13.75	6.08
Fushun	33.66	1.78	3.35	1.65	4.84	1.59	3.91	1.73
Benxi	35.16	1.86	3.75	1.85	5.47	1.79	4.23	1.87
Dandong	66.11	3.51	6.64	3.27	10.46	3.43	7.58	3.35
Jinzhou	193.63	10.27	22.91	11.28	35.86	11.75	24.26	10.72
Yingkou	62.29	3.30	5.58	2.75	8.39	2.75	6.83	3.02
Fuxin	194.65	10.32	20.28	9.99	28.29	9.27	23.32	10.31
Liaoyang	32.72	1.74	3.71	1.83	5.55	1.82	4.04	1.79
Panjin	66.47	3.52	6.90	3.40	11.60	3.80	7.64	3.38
Tieling	220.41	11.69	24.53	12.08	37.10	12.16	26.84	11.86
Chaoyang	285.78	15.16	29.86	14.71	42.67	13.98	34.11	15.07
Huludao	134.28	7.12	15.16	7.47	23.70	7.77	16.43	7.26

.

In 2023, the nutrient content in livestock manure resources in Liaoning Province was very high, and the nutrient content was different in each city. In terms of the nutrient content provided by livestock manure, Chaoyang provided the highest amounts of OM, N, P, and K, with amounts of 2.86 × 10⁶ t, 29.86 × 10⁴ t, 42.67 × 10⁴ t, and 34.11 × 10⁴ t, respectively. The nutrient content of Shenyang manure was the second highest, and the nutrient content of livestock manure resources in Fushun was the lowest in the province. Due to the different breeding strategies in each city, the nutrient contents were different due to differences in excretion parameters, feeding cycles, and breeding numbers.

3.2.2. Fertilization Analysis of Livestock Manure in Liaoning Province

The amount of manure applied as fertilizer in Liaoning Province in 2023 is shown in

Table 7. The amount of manure applied as fertilizer in each city of Liaoning Province.

Area	Total (104 t)	N Fertilizer (104 t)	P Fertilizer (104 t)	K Fertilizer (104 t)	Compound Fertilizer (104 t)
Total Province	137.6	47.2	9.2	10.8	70.4
Shenyang	19.1	6.7	1.3	2.2	9.0
Dalian	14.3	4.5	1.1	1.6	7.0
Anshan	10.1	2.6	0.3	0.6	6.7
Fushun	3.2	1.6	0.4	0.3	1.0
Benxi	1.1	0.7	0.1	0.1	0.3
Dandong	6.2	3.2	0.3	0.4	2.3
Jinzhou	16.4	6.7	0.7	1.1	7.8
Yingkou	4.9	2.4	0.7	0.7	1.1
Fuxin	14.5	4.0	0.3	0.6	9.6
Liaoyang	4.7	1.6	0.6	0.4	2.2
Panjin	3.8	1.6	0.4	0.3	1.5
Tieling	21.8	3.8	0.9	0.9	16.2
Chaoyang	9.7	4.8	1.3	0.7	2.8
Huludao	7.7	2.9	0.9	0.9	3.0

. In 2023, the amount of manure applied as fertilizer in this province was 1.38 × 10⁶ t, of which the amount applied as N fertilizer was 47.2 × 10⁴ t, the amount applied as P fertilizer application was 9.2 × 10⁴ t, and the amount applied as K fertilizer was 10.8 × 10⁴ t. The compound amount applied as fertilizer was the largest, amounting to 70.2 × 10⁴ t, accounting for more than 50% of the total.

The formula for calculating the rate at which the nutrient content of livestock manure resources is substituted for chemical fertilizer is as follows.

Fertilizer substitution rate = nutrient content of livestock manure/fertilizer application rate.

The rates at which the nutrient content of livestock manure resources was substituted for chemical fertilizer in Liaoning Province in 2023 are shown in

Table 8. Rates at which the nutrient content of different livestock manure resources were substituted for fertilizer.

Type of Livestock Manure	N (%)	P2O5 (%)	K2O (%)
Pig manure	172.12	1538.04	689.54
Cattle manure	94.49	463.04	518.89
Sheep manure	23.05	92.93	184.54
Poultry manure	140.51	1223.37	702.59
Total	430.17	3316.88	2095.56

.

The rate at which the N content in livestock manure was substituted for nitrogen fertilizer reached 430.17%. The rate at which the P₂O₅ content in livestock manure was substituted as P fertilizer was 3316.88%. The rate at which the K₂O content in manure resources was applied as fertilizer was 19.54 times the K fertilizer application rate.

The substitution rate of nutrients in livestock manure for fertilizer in Liaoning Province is shown in Figure 4. In terms of the substitution rate of nitrogen nutrients in livestock manure for N fertilizer, Chaoyang and Tieling had the largest substitution potential. In terms of the substitution potential of P in livestock manure for P fertilizer, Anshan and Fuxin had significantly greater substitution potentials than other cities. The substitution potential of K in the livestock manure of Fuxin, Benxi, and Chaoyang for K fertilizer was greater than that of other cities. From the perspective of the total province, Fuxin had the largest substitution potential of total nutrients in livestock manure resources for chemical fertilizer. The substitution potential of total nutrient content in livestock manure for fertilizer application rate was Fuxin > Benxi > Anshan > Chaoyang > Tieling > Jinzhou > Panjin > Dandong > Dalian> Huludao > Shenyang > Fushun > Yingkou > Liaoyang.

To further illustrate the potential of the nutrients in livestock manure to replace fertilizer, the values were converted into the annual reduction in fertilizer inputs. To facilitate this calculation, the nutrients (N-P₂O₅-K₂O) in manure were converted into CO(NH₂)₂ (46%), Ca(H₂PO₄)₂ (12%), and K₂SO₄ (50%). The calculation was carried out according to the following rates: CNY 2400/t of CO(NH₂)₂, CNY 1500/t of Ca(H₂PO₄)₂, and CNY 4200/t of K₂SO₄. The results are shown in

Table 9. Economic conversion of substituting fertilizer with livestock manure in Liaoning Province.

Area	Conversion of Manure Instead of Chemical Fertilizer
	N (104 t)	Conversion Amount of CO(NH2)2 (104 t)	P2O5 (104 t)	Conversion Amount of Ca(H2PO4)2 (104 t)	K2O (104 t)	Conversion Amount of K2SO4 (104 t)	Economic Conversion (108 CNY)
Shenyang	26.71	58.07	37.24	310.33	29.71	59.42	85.44
Dalian	21.39	46.50	34.44	287.00	23.65	47.30	74.08
Anshan	12.26	26.65	19.55	162.92	13.75	27.50	42.38
Fushun	3.35	7.28	4.84	40.33	3.91	7.82	11.08
Benxi	3.75	8.15	5.47	45.58	4.23	8.46	12.35
Dandong	6.64	14.43	10.46	87.17	7.58	15.16	22.91
Jinzhou	22.91	49.80	35.86	298.83	24.26	48.52	77.16
Yingkou	5.58	12.13	8.39	69.92	6.83	13.66	19.14
Fuxin	20.28	44.09	28.29	235.75	23.32	46.64	65.53
Liaoyang	3.71	8.07	5.55	46.25	4.04	8.08	12.27
Panjin	6.90	15.00	11.60	96.67	7.64	15.28	24.52
Tieling	24.53	53.33	37.10	309.17	26.84	53.68	81.72
Chaoyang	29.86	64.91	42.67	355.58	34.11	68.22	97.57
Huludao	15.16	32.96	23.70	197.50	16.43	32.86	51.34
Total province	203.03	441.37	305.16	2543.00	226.30	452.60	677.47

.

The input of livestock manure used to replace chemical fertilizer in Liaoning Province could be reduced by CNY 67.75 billion (Table 9). The top three cities in this regard were Chaoyang (CNY 9.76 billion), Shenyang (CNY 8.54 billion), and Tieling (CNY 8.17 billion), and the cost of using livestock manure to replace chemical fertilizer to reduce the input was the smallest in Fushun (CNY 1.11 billion). The abundant livestock manure resources in Chaoyang and other cities should be used, combined with local economic and social development levels, to promote the return of livestock manure to the fields and reduce the economic costs of the application of chemical fertilizer.

3.3. Energy Potential of Livestock Manure in Liaoning Province

Using Formulas (3) and (4) and the parameters in Table 3, the standard coal and biogas production converted from livestock manure in Liaoning Province in 2023 was calculated. The results are shown in

Table 10. Energy potential of livestock manure in Liaoning Province.

Type of Livestock Manure	Livestock Manure Resources (104 t)	Available Resources (104 t)	Standard Coal (104 t)	Biogas (107 m3)
Pig manure	3562.98	3562.98	1532.08	712.60
Cattle manure	2859.11	1715.47	806.27	514.64
Sheep manure	830.26	498.16	264.02	149.45
Poultry manure	3188.43	1913.06	1224.36	573.92
Total	10,440.78	7689.67	3826.73	1950.61

.

If the livestock manure in Liaoning Province in 2023 was fully utilized to generate energy, it could be converted into 3826.73 × 10⁴ t of standard coal or 1950.61 × 10⁷ m³ of biogas. As the leading breeding industry in Liaoning Province, pig farming had the largest amount of energy that could be generated from manure: it was higher than that of other manures, equivalent to 1532.08 × 10⁴ t of standard coal and 712.60 × 10⁷ m³ of biogas. Poultry was next: if poultry manure were to be completely converted into energy, it would be equivalent to 1224.36 × 10⁴ t of standard coal and 573.92 × 10⁷ m³ of biogas. Finally, there was the manure of cattle and sheep, which could be converted into slightly lower amounts of energy, namely, 806.27 × 10⁴ t and 264.02 × 10⁴ t of standard coal and 514.64 × 10⁷ m³ and 149.45 × 10⁷ m³ of biogas, respectively.

Using the method noted in this section, the energy potential of livestock manure in each city in Liaoning Province was calculated and compared with the energy consumption of each city. The results are shown in

Table 11. Energy potential of livestock manure resources in each city in Liaoning Province.

Area	Livestock Manure Resources (104 t)	Standard Coal (104 t)	Biogas (107 m3)	Energy Consumption (104 t Standard Coal)	Standard Coal/Energy Consumption (%)
Shenyang	1428.7	498.64	267.27	782.3	63.74
Dalian	1052.47	399.44	194.94	3647.2	10.95
Anshan	609.64	228.54	112.21	1843.6	12.40
Fushun	178.97	63.64	33.06	1039.2	6.12
Benxi	196.85	71.02	36.81	1347.1	5.27
Dandong	334.78	124.48	61.44	226.3	55.01
Jinzhou	1131.37	431.98	215.18	309.8	139.44
Yingkou	296.35	107.38	53.85	1659.7	6.47
Fuxin	1096.59	389.56	205.73	502.5	77.53
Liaoyang	190.08	70.12	35.91	998.8	7.02
Panjin	330.01	127.99	60.54	1440.7	8.88
Tieling	1249.01	456.39	233.20	518.1	88.09
Chaoyang	1590.89	569.14	297.39	1038.5	54.80
Huludao	755.07	288.41	143.06	579.2	49.79

and Figure 5.

As shown in Table 11 and Figure 5, the city with the greatest energy potential for livestock manure was Chaoyang, which reached 569.14 × 10⁴ t of standard coal. The lowest energy potential for livestock manure was Fushun, with only 33.06 × 10⁷ m³ of biogas, and this result is consistent with the distribution of livestock manure resources. The order regarding the potential for the conversion of livestock manure resources into standard coal in Liaoning Province was as follows: Chaoyang > Shenyang > Tieling > Jinzhou > Dalian > Fuxin > Huludao > Anshan > Panjin > Dandong > Yingkou > Benxi > Liaoyang > Fushun.

The livestock manure resources in each city were converted into standard coal and compared with their energy consumption. Evidently, the energy potential of livestock manure in Jinzhou exceeded its energy consumption, reaching 139.44%, indicating that it can be completely replaced. In addition, the energy potential of livestock manure in Tieling, Fuxin, Shenyang, and Chaoyang accounted for more than 50% of energy consumption. However, the energy potential of livestock manure in Benxi only accounted for 5.27% of its energy consumption, which was the least in Liaoning Province. In general, although the energy potential of livestock manure varied in each city, it was possible to reduce energy consumption by converting local livestock manure into energy, thereby reducing pollution and promoting environmental protection.

4. Discussion

4.1. Estimation of Livestock Manure Resources and Nutrient Content

There have been many studies on the estimation of livestock manure resources and nutrient content, but there are some deviations in the calculation results. Systematic studies have been conducted on livestock manure resources in developed countries [26]. In China, there is no unified method for calculating livestock manure resources. Most researchers use the excretion coefficient method [27]. Previous studies have shown that, in 2010, there was 4.23 × 10⁹ t of livestock manure resources in China, while another study suggested a figure of 2.26 × 10⁹ t [28,29]. The difference between these data is mainly caused by the different kinds of livestock and poultry analyzed, the different feeding periods of livestock and poultry, inconsistent estimation methods, and an inconsistent selection of excretion coefficients [30]. The excretion coefficient of livestock and poultry is the basis of animal husbandry environmental management. However, the environmental management of animal husbandry started late in China, and there is no definite excretion coefficient. Moreover, the excretion coefficient will change due to feeding methods, feeding cycles, seasons, and other factors. When studying livestock manure resources, researchers have chosen the excretory coefficient of livestock and poultry relevant to their research according to their own understanding [28,29,31,32,33]. Although the methods of calculating the excretion coefficient were different, the research results all showed that there is a massive quantity of manure resources in the livestock and poultry breeding industry in Liaoning Province, one rich in nutrient resources and associated with a high fertilizer substitution rate.

Based on the analysis, there was a massive amount of livestock manure in Liaoning Province in 2023, and it was mainly composed of pig, cattle, and poultry manure. Due to the differences in the excretion parameters and feeding cycles of different livestock and poultry animals, the resources of livestock manure were not proportional to the amount of feeding. Pigs were the main source of livestock manure in Liaoning Province because of their large body sizes, the large amounts of food they eat, their long feeding cycles, and the large amounts of waste they excrete daily. Although poultry animals are small, have short feeding cycles, and excrete small amounts of waste daily, they were the second largest source of livestock manure in Liaoning Province because of the large amounts of feed they consume. Cattle contributed fewer manure resources than pigs and poultry, and sheep contributed the least. Chaoyang, Shenyang, and Tieling ranked among the top three cities in terms of the amount of organic fertilizer converted from livestock manure and the economic conversion of alternative chemical fertilizers. The government should make use of the abundant local resources and combine local economic and social development levels and the development of the livestock and poultry breeding industry to promote regional farming and breeding and commercial organic fertilizer production and build a modern integrated farming and breeding system.

Based on the results of the assessment of the potential for fertilizing livestock manure in Liaoning Province, we preliminarily estimated the potential value of fertilizing livestock manure in China according to the number of livestock and poultry farmed in the country. According to the data in Statistical Communiqué on the 2023 National Economic and Social Development of the People’s Republic of China, in 2023, the livestock and poultry farming quantities of pigs, cattle, sheep, and poultry in China are, respectively, 72.6 × 10⁷, 5.02 × 10⁷, 33.8 × 10⁷, and 16.82 × 10⁹. The resources of major livestock and poultry manure in China and their potential for fertilization were converted according to the assessment method above. The conversion results show that China’s livestock manure can provide organic matter, nitrogen, phosphorus, and potassium with contents of 35.97 × 10⁷ t, 3.87 × 10⁷ t, 5.78 × 10⁷ t, and 4.35 × 10⁷ t, respectively. Based on the nutrient equivalence, collecting these livestock manures for harmless treatment and using them in agricultural production can reduce the application of fertilizers such as about 8.41 × 10⁷ t CO(NH₂)₂, 48.91 × 10⁷ t Ca(H₂PO₄)₂, and 8.7 × 10⁷ t K₂SO₄. The use of livestock manure as a substitute for chemical fertilizers can effectively improve the comprehensive utilization rate of livestock manure, reduce its negative impact on the ecological environment, and, at the same time, can reduce China’s dependence on chemical fertilizers and raw materials, improve soil fertility, promote the growth of crops, and realize the sustainable development of agriculture [34].

4.2. Analysis of the Energy Utilization Potential of Livestock Manure

The biogas potential of Liaoning Province in 2023 was 1950.61 × 10⁷ m³. The total rural population of Liaoning Province was 1186.54 × 10⁴ at this time, so each person could be allotted 1644 m³ of biogas. According to the calculations, there were 3.5 people in each household, so each household could make use of 5754 m³ of biogas resources, a figure much higher than the national average of 1184.3 m³ [35]. At present, most biogas projects in Liaoning Province are idle, and the overall technical content of these projects is low. For large livestock and poultry farms, large- and medium-sized biogas projects should be built, support for grid-connected biogas power generation should be increased, and a subsidy policy for grid-connected biogas power generation should be implemented [36]. For small-scale farming areas, black-film biogas digesters could be built to reduce construction and operation costs [37]. Biogas derived from animal manure can be directly used for power generation, heating, or domestic gas, with standardized technical process and stable operation, and biogas slurry and residue can be processed into solid or liquid organic fertilizer through aerobic fermentation, forming a double income model of “biogas + organic fertilizer”. Biogas power generation can meet the demand for electricity for farm production, and the remaining electricity can be integrated into the power grid or slated for self-use, reducing energy costs. Biogas can also be used for the daily life of staff, feed processing, and heating, reducing dependence on coal and lowering fuel expenses. While traditional manure treatment entails high environmental protection costs, biogas projects reduce pollutant emissions through resource utilization, avoid environmental fines, and may be subsidized by the government. Additionally, biogas, as a renewable energy source, can be used in the carbon trading market, further increasing a project’s revenue. The economic feasibility of converting livestock manure into biogas is high, and the core of this process lies in mature technology, a multi-product income chain, and policy support. In the process of energy utilization, various limiting factors should be considered. Before developing biogas, detailed investigations and research should be performed, and different policies and methods should be adopted in order to utilize biogas resources according to local conditions [38].

Based on the results of the assessment of the energy potential of livestock manure in Liaoning Province and combined with the number of livestock and poultry farms in China in 2023, we calculated the amount of major livestock manure resources and discounted their potential for energy utilization. The results show that, if the livestock manure produced in China in 2023 is fully utilized as an energy source, it can be converted into approximately 7.47 × 10⁸ t of standard coal or 3802.6 × 10⁸ m³ of biogas. If this biogas is used to replace natural gas as a household energy source, it can supply about 70% of China’s annual natural gas consumption. If all of this energy is used to generate electricity, about 45 billion kWh of green power can be generated annually, which is equivalent to 57% of the annual power generation of the Three Gorges Power Station in 2022. This indicates that it has a huge potential for energy substitution.

4.3. Suggestions for Rational Resource Utilization of Livestock Manure

We evaluated the potential of livestock manure for fertilizer and energy utilization in various cities of Liaoning Province. Additionally, we initially estimated the actual value of the resource utilization of major livestock manure in China in 2023. From these efforts, it is clear that, if livestock manure can be effectively managed and utilized, it can provide great economic, social, and ecological value to all aspects of production, life, and ecology in China. Therefore, based on the current utilization potential of livestock manure in Liaoning Province, we propose the following countermeasures and recommendations for the efficient utilization of livestock manure resources both in Liaoning Province and across China in the future.

(1)

In order to effectively enhance the utilization rate of livestock manure resources, the organic combination of planting and farming should be vigorously promoted, and biogas digesters should be established in farming areas as appropriate. In some Chinese cities and villages where livestock and poultry farming is the main industry, such as Chaoyang City in Liaoning Province, Zhengzhou City in Henan Province, and Chengdu City in Sichuan Province, where hog farming is on a large scale; Zhangye City in Gansu Province, Chifeng City in Inner Mongolia Autonomous Region, and Fuxin City in Liaoning Province, where cattle and sheep farming is on a large scale; and Weifang City in Shandong Province, Foshan City in Guangdong Province, and Dalian City in Liaoning Province, where poultry (chicken) farming is on a large scale, efforts should be made to develop three-dimensional agriculture, making full use of land resources and space for planting and breeding at different levels. It is recommended to promote the model of raising chickens and sheep in orchards and under forests in these areas. At the same time, local governments or relevant entities should build biogas digesters in cities with large-scale pig farming. This can realize the comprehensive utilization of animal and poultry manure for fertilizers and energy under low-cost conditions. Moreover, due to natural free-range farming, the quality of the meat and eggs of poultry and livestock will be improved. This will increase the profitability of farming, save the cost of feed, and enhance the efficiency of the region’s energy supply. In this way, it can enable the animal husbandry, planting, and energy industries to form a virtuous cycle of ecological and organic development, achieving a win-win situation for planting, breeding, energy, and livestock and poultry waste resources.

(2)

Although there are various ways to utilize livestock manure for fertilizer and energy, each of them needs to be combined with the actual natural conditions, environmental conditions, and social needs of the region to determine the specific development mode for livestock manure utilization. For example, Liaoning Province is located in the typical temperate monsoon climate zone in Northeast China. With low winter temperatures, strong soil absorption capacity, and a high carrying capacity for livestock manure nutrients, it is more suitable for using livestock manure as fertilizer. And, in the desert areas in the inland northwest, such as the desert area in Gansu’s Hexi Corridor, it is not suitable to promot the use of livestock manure as fertilizer. In these areas, when livestock manure is applied to the soil, it is difficult for the organic components to decompose quickly in the dry environment into nutrients that can be absorbed by plants, which may, due to a lack of water, lead to the accumulation of salts in the fertilizer. Also, in coastal areas such as Guangdong Province and Fujian Province, promoting the use of livestock manure as fertilizer is not suitable. During the typhoon season, the strong rainfall will cause the livestock manure applied to the soil to be washed away by the rain before it has time to be adsorbed by the soil and absorbed by plants. This not only results in a waste of fertilizer, but also in the runoff being carried into a body of water, causing water pollution and other environmental problems. However, for some energy shortage areas in China, such as Hebei Province in North China, which is densely populated, with a high consumption of energy for industry and residential life, and facing the problems of the tight supply of traditional energy sources such as coal and environmental protection pressures, the energy use of livestock manure can help to increase the supply of clean energy and optimize the energy structure. In addition, in some ecologically fragile areas such as Inner Mongolia, Gansu, and Ningxia, since traditional energy acquisition methods such as the over-exploitation of coal may cause greater damage to the ecological environment, using livestock manure to produce biogas and other clean energies can reduce the dependence on traditional energy sources. At the same time, it can decrease the impact of traditional energy use and livestock and poultry waste emissions on the ecological environment, achieving a win-win situation between ecological protection and economic development. Therefore, according to the actual natural conditions and economic and social development needs of each place, combined with the results of the evaluation of the potential for fertilizer and energy utilization of livestock manure in the region, the most appropriate ways of resource utilization should be weighed and determined to achieve the maximization of the economic, social, and ecological benefits of the utilization of livestock manure resources.

(3)

The key problems affecting soil health and agricultural product safety in regard to the use of livestock manure as fertilizer are heavy metals and antibiotic residues. In order to reduce the effect of heavy metals and antibiotics in manure during fertilization, adsorbent materials such as biochar, zeolite, and clay have been added in the composting process to immobilize heavy metals and reduce their bio-effectiveness. The high-temperature period of composting should be increased (above 55 °C), and thermochemistry should be used to degrade antibiotics such as tetracyclines and sulfonamides. Non-edible crops (e.g., energy plants) or species with low heavy metal uptake should be planted in areas subjected to a high risk of pollution. In terms of management and policy, mandatory standards should be developed for the use of livestock manure as fertilizer (e.g., heavy metal limits, antibiotic residue thresholds), and a system for certifying the quality of manure should be established to prevent excess manure from entering farmland. Through implementing the above multi-dimensional measures, the potential risks heavy metals and antibiotics pose to the environment and human health can be effectively reduced, all while ensuring the resourceful utilization of livestock manure, thus promoting the green and sustainable development of agriculture.

5. Conclusions

By measuring the amount of livestock manure resources in Liaoning Province in 2023, we analyzed the potential and value of livestock manure in Liaoning Province in terms of fertilizer and energy utilization, and preliminarily extrapolated the analysis results to the potential of livestock manure resource utilization in China. The main conclusions obtained from this study are as follows.

(1)

Liaoning Province is rich in livestock manure resources, possessing a total amount of 104.41 × 10⁶ t. In 2023, the amounts of pig, cattle, sheep, and poultry manure were 35.63 × 10⁶ t, 28.59 × 10⁶ t, 8.30 × 10⁶ t, and 31.88 × 10⁶ t, respectively.

(2)

The amount of livestock manure in Liaoning Province in 2023 can be converted into organic matter (OM), nitrogen (N), phosphorus (P), and potassium (K) of 18.86 × 10⁶ t, 2.03 × 10⁶ t, 3.05 × 10⁶ t, and 2.26 × 10⁶ t, respectively. And, all these nutrients can be used for fertilization to completely replace the amount of fertilizers used in Liaoning Province.

(3)

When all livestock manure generated in Liaoning Province in 2023 is utilized for energy purposes, it can be converted into 3826.73 × 10⁴ t of standard coal or 1950.61 × 10⁷ m³ of biogas, which indicates a significant potential for energy substitution in the region.

(4)

The results of this study can be used as a reference for estimating the potential of livestock manure fertilizer and energy utilization in China and globally, which is of great significance for achieving the efficient utilization of livestock manure resources.