Policies and regulations for promoting manure management for sustainable livestock production in China: a review

Livestock numbers in China have more than tripled between 1980 and 2017. The increase in the number of intensive livestock production systems has created the challenges of decoupled crop and livestock systems, low utilization of manures in croplands, and subsequent environmental pollution. Correspondingly, the government has enacted a series of policies and regulations to increase the sustainability of livestock production. This paper reviews the objectives of these policies and regulations and their impacts on manure management. Since 2017 there have been two policy guides to speed up the appropriate use of manures, three action plans for increasing manure recycling, and one technical guide to calculate nutrient balances. Requirements of manure pollution control and recycling for improved environmental performance of livestock production systems were included in three revised environmental laws. Most recent survey data indicate that the utilization of livestock manures was 70% in 2017, including that used as fertilizer and/or for production of energy. The targets for manure utilization are 75% in 2020 and 90% in 2035. To achieve these targets and promote ‘green

livestock production', additional changes are needed including the use of third-party enterprises that facilitate manure exchange between farms and a more integrated manure nutrient management approach.

Introduction
Livestock products contribute 17% to the total food energy consumption and 33% to the total protein consumption by humans globally but there are large differences between developed and developing countries [1] . In developed countries the per capita rate of consumption of livestock products is plateauing, but in developing countries the consumption of livestock products (and hence livestock production) is increasing [1][2][3] .
The livestock industry in China has experienced rapid growth and a vast transition driven by economic incentives over the last four decades [3,4] . The number of livestock (livestock units) has increased threefold between 1980 and 2017. Livestock production has increased even more; total meat, egg and milk production increased 6.0, 10.7 and 12.0 times between 1980 and 2017 [5,6] . The spatial distribution of manure nitrogen (N) and phosphorus (P) excretion by livestock (calculated by the total number of animals per category per province [7] and animal categoryspecific N and P production coefficients [8] ) indicates that 'hotspots' of manure production are concentrated on the North China Plan and in central, south and east China.
Increased specialization of livestock systems has resulted in the decoupling of crop and livestock production systems [11,[18][19][20] and in a reduction in manure use efficiency. Therefore, a greater integration of crop and livestock production systems is one of the key strategies for increasing the resource use efficiency of livestock manures [21] . To address the environmental challenges of livestock production, many countries including the United States of America (USA) and EU countries have introduced agri-environment policies and action plans to promote efficient and low emission livestock production systems since the 1990s [22][23][24] . This paper reviews the objectives and targets of agri-environment policies and regulations in China and assesses their impact on manure management. Based on the review, we propose a number of suggestions to further improve manure utilization. These suggestions provide a reference for the sustainable development of livestock production in developing countries including China.

Challenges of livestock manure utilization in China
In recent years the Ministry of Agriculture and Rural Affairs (MARA), Ministry of Finance (MF), Ministry of Science and Technology (MST) and other ministries have actively promoted the utilization of livestock manure [25][26][27] . However, over 70% of farms including crop production and/or livestock production in China were specialized crop production systems or specialized livestock production systems in 2017 [28] . This specialization has created barriers for effective manure utilization in croplands as indicated below.

Small crop farms separated from large livestock farms
Nutrients from organic manures supplied over 90% of the total nutrients applied to croplands in China in the 1950s [29] . The increase in demand for livestock products caused by the increased population and consumption per capita has led to a rapid increase in the proportion of large-scale livestock farms without cropland [4] . This has contributed to the separation of crop and livestock farms both in space and scale [30] . The proportion of pigs reared in farms with > 500 finishing pigs per farm increased from 8% in 1998 to 47% in 2017. In contrast, crop production is still dominated by small-scale farmers who often work part-time in the cities [31] .
This situation is likely to continue for some time [31] . The area cultivated on farms with > 50 mu (3.3 ha) accounted for about 18% of the total cultivated area in 2016 [31] . According to the Technical Guideline for the Calculation of the Land's Capacity to Receive Livestock Manure, an area of 50.0 mu (3.3 ha) can receive manure N produced by 500 finishing pigs [32] . The gap between the proportion of livestock farms with > 500 finishing pigs and the proportion of crop farms with over 50 mu (3.3 ha) results in a low utilization of livestock manure in croplands.
Currently, only 30% of total excreted N and 48% of excreted P are returned to the land via manure application [11] .

Variable and low nutrient contents in manures
Manure is an excellent source of the major plant nutrients including N, P, and K [33] and it provides many of the micro nutrients that plants require [34,35] together with organic matter for soil amendment, all of which contribute to boosting crop yields and nitrogen use efficiency (NUE) [36][37][38][39][40][41] . However, manure nutrient content and availability are often highly variable and unknown. Labels for composted manure may only provide a sum of all nutrients [19] , and this is not sufficiently informative for precision fertilization.
Furthermore, the cost of applying manures is high, about twice that of mineral fertilizers [42] , due to the large volume, high water and low nutrient contents, and especially the high transport costs, compared with mineral fertilizers. There is also a requirement for liquid manures to be treated before they can be used on croplands [43] , and this increases the costs and may also reduce the nutrient value (especially N) if the manures are composted. Therefore, the market competitiveness of manures is much lower than that of mineral fertilizers.

Risks of heavy metals and antibiotics in manures
Another issue is the possible contamination of manures with trace metals (loid) and antibiotics [44,45] . The content of heavy metals (notably copper and zinc) of some pig and chicken manures exceeds the national requirements of the Control Standard for Pollutants in Sludge from Agricultural Use in some regions due to the use of feed additives [43,46] . Frequent applications of manure will result in the accumulation of heavy metals and antibiotics in soils and crops [44] , with potential adverse effects on human health.

Lack of enterprises and services for manure redistribution
In the Netherlands, private companies overseen by the government redistribute manures between livestock farms and crop farms. Livestock farmers have to pay 10 to 25 Euro per tonne of manure to these trading companies, and crop farmers receive 1-14 Euro per tonne, depending on manure quality and the distance between farms [47] . Each truck load of manure (about 30 tonnes) is weighed and the N and P contents are determined. This type of trading/management scheme is not yet available in China. There are many challenges in establishing a professional manure redistribution system, such as (i) who should pay for the prolonged manure storage and application infrastructure, (ii) who should pay for the manure transportation, (iii) who should receive government subsidies, and (iv) who should monitor and control the flow of manure and money. The lack of appropriate manure application equipment and manure storage facilities and the high costs of manure transportation [48,49] are barriers to the use of manures by crop farmers. All of these factors have contributed to a fractured manure management chain and to low manure nutrient utilization in Chinese croplands.

Experiences in the United States and the European Union
Many developed countries including the USA and some EU countries experienced a period of serious pollution during the rapid development of intensive livestock farming in the second half of the twentieth century. In response, governments and livestock industries implemented a series of policies, action plans and guidance to reduce the environmental burden from livestock production. Livestock manures are now considered as valuable sources of nutrients [33] and organic matter [38] which have to be stored in contained manure stores and have to be applied to croplands during the growing season according to crop nutrient demand. Major improvements have also occurred through increased animal productivity, animal breeding, and improved animal feeding and housing. However, the separation and concentrations of specialized livestock farms and crop production systems remains a bottleneck in improving manure management in these countries (see other papers in this special issue) In the USA, farmers or their advisers have to make comprehensive nutrient management plans for addressing potential water quality and public health impacts associated with animal feeding operations [50,51] . When the nutrient supply via livestock manure exceeds the nutrient demand of crops, farms have to choose other methods to treat and use the manure. However, only small proportions of manures are processed in practice, for example by composting or anaerobic digestion [52] .
Livestock farmers in the EU also have to make a nutrient management plan and have to comply with manure application limits and additional regulations related to manure storage and manure application timing and method, according to action plans to comply with the Nitrates Directive [24] . A uniform manure application limit of 170 kg N ha -1 yr -1 has been set across the EU, although a derogation is possible for N-demanding crops with a long growing season (permanent crops) [24] . Application of fertilizers and manures is restricted to the growing season only. Further, farmers are encouraged to use low-protein animal feeds and reduce ammonia emissions by low-emission animal housing and manure storage systems, and by lowemission manure application (through injection, trailing hose or rapid incorporation into the soil) [53] .

Government policies, laws and regulations in China
Until 2015 the main objective of government policies, laws and regulations related to manure management in China was simply pollution control. Since 2015 the objectives of the policies, laws and regulations have expanded to include pollution control and enhanced resource use efficiency.
The environmental problems caused by the rapid development of livestock production have emerged rapidly (Table 1). The NH3 emissions from livestock production have increased from 2.9 Tg in 1980 to 4.8 Tg in 1997 [17] . Non-CO2 GHG emissions from livestock production have increased from 149 Tg in 1980 to 212 Tg in 1997 [6,54] . The nutrients from organic manures as a percentage of to the total amounts of nutrients from fertilizers applied to croplands decreased from 47.1% in 1980 [55] to 23.6% in 2008 [56] . In consequence, N use efficiency in the food system has decreased steadily [4,57] . As a result, increasing quantities of livestock manures, sewage sludge and other organic resources have been neglected and not effectively re-utilized in crop production, but have instead been lost to soils, waters and air [9][10][11][12][13][14][15][16] .  b Percentage of manure comprehensive utilization refers to the ratio of utilized manure as resources (like compost, biogas and land application) to the amount of fresh manure production.
c Value according to Zhang, 2001 [55] ; d Value according to Niu and Ju, 2017 [56] e Value according to EPA, 2002 [72] ; f Value according to MARA, 2019 [73] ; In response, the government has gradually implemented policies and regulations related to manure management from 2000 (Table 2a) [59] , and the adoption of the sustainable development goals (SDGs) by all United Nations member states in 2015 have boosted the thinking about sustainable livestock production in China [60] . Gradually, manure pollution control measures have been replaced with policy and advice to promote manure resource recycling and use (Table 2b).  (Table 2b). The government has also provided a technical guide to calculate the maximum number of animals per farm based on the land area per farm and the balance of manure nutrient supply and crop nutrient demand. Further, nitrogen vulnerable zones have been proposed [30] . In 2017 a policy guidance document was issued to accelerate the utilization of livestock manures in croplands. This involved the establishment of a livestock manure use system and the development of mechanisms to improve integration of crop and livestock systems by 2020 [27] . It also set the target for manure utilization to be at least 75% by 2020. Hence, a minimum of 75% of produced livestock excreta needs to be applied to cropland by 2020. Further, at least 95% of large-scale livestock farms must have infrastructure for manure treatment [27] .
Another guide to promote manure application to cropland and to strengthen pollution control was issued in 2019 [25] . This guide sets the targets for comprehensive utilization of The Environmental Protection Law revised in 2014 introduced the regulatory regime for discharge permits [62] . Enterprises and institutions discharging pollutants in excess of the prescribed national or local discharge standards are required to pay levies that are used for the treatment of polluted surface waters.
The Law on the Prevention and Control of Atmospheric Pollution was revised in 2018.
The revised version stipulates the development of circular agriculture and provides support for manure treatment [63] . This law requires all livestock farms and communities to collect, store, transport and use sewage sludges, manures and livestock carcasses in a timely manner and use safe treatment practices to prevent the emissions of odor, nitrogen oxides (NOx) and GHGs.

The Law on the Prevention and Control of Water Pollution (2018) supports the construction of facilities for the safe treatment of manures and wastewaters on livestock farms
and in communities [64] . It stipulates that livestock farms and communities must ensure the normal operation of their facilities for the safe treatment of manures and ensure that wastewater discharge meets the required standards (total N, 40 mg L -1 ; NH3-N, 25 mg L -1 ) [65] or meet the quality standard for cropland irrigation water in China [43] . If livestock wastewater is applied through irrigation channels the water quality of the nearest irrigation water intake downstream must be guaranteed to meet the water quality standard for irrigation. Local governments are responsible for organizing the collection, centralized treatment and subsequent use of livestock manures in counties with small scattered livestock farms.

Additional actions for improving manure management
In addition to the governmental policies, laws and regulations discussed in section 3.2, a series of additional actions and financial incentives have been implemented to improve the effectiveness of the government policies, laws and regulations.
The Action Plan for Water Pollution Control (2015) aims at closing or relocating livestock farms in designated (prohibited) areas (Table 3). This plan has led to the transfer of numerous livestock farms from areas close to rivers and lakes to areas with dryland and relocation of pigs from the south to the north of Chain to protect watercourses [66] . An action plan for the recycling (land application) of livestock manures (2017-2020) introduced seven technological options: (1) full manure collection and land application, (2) specialized biogas plants, (3) composting of solid manures, (4) treatment of manures with high-rise fermentation beds, (5) litter recycling, (6) wastewater recycling, and (7) treatment of manures to meet discharge standards [26] (Figure 1). Livestock farms must choose one or more of these seven options.  [67,68] . In addition, subsidies have been provided to poultry farms to reduce the spillage of drinking water, and to pig farms to reduce the amounts of flushing water used [58] . Subsidies have also been provided for odor control and for closed storage and treatment of liquid manures from 2020 [69] .
Another action plan has stimulated the replacement of mineral fertilizers by organic fertilizers in the production of fruit, vegetables and tea in 100 counties through subsidies worth one billion RMB [70] . The goal is to reduce mineral fertilizer consumption by 20 to 50% in fruit, vegetable and tea production by 2020.

A Technical Guideline for the Calculation of the Land's capacity to Receive Livestock
Manure was released in 2018 and provides a standard calculation method for recycling manures [32] . It is based on the nutrient input-output balance. The nutrient requirements of crops are determined according to crop type and yield, soil fertility level, and the proportion of nutrients supplied by manures. The nutrient supply from livestock manures is determined according to the number of livestock, livestock-specific excretion factors, and the manure collection and treatment.

Main effects
Total manure recycling was < 60% in 2015 [71] and as much as 70% by the end of 2017. Manure treatment facilities for large-scale farms were present on < 20% of the total number of large farms in 2000 [72] and on 80% in 2019 [73] ( Table 1).
Water use and spillage have been greatly reduced on pig and poultry farms. As a consequence, the total volume of manure has also decreased dramatically. This has facilitated the transport of manure to crop farms [58] .
The amount of mineral fertilizer used in tea, vegetable and fruit production in the aforementioned 100 counties has dropped by 18%, and organic fertilizer use has increased by 50%, and this has increased resource use efficiency [70] . Organic fertilizers have also contributed to increases in soil organic matter content [36][37][38][39][40][41] and to an improved quality of agricultural products (higher contents of micronutrients) [36][37][38][39][40][41] . However, farmers often perceive that the subsidies are too small and the pilot areas that have benefited from the subsidies are often limited in scale and duration. There is still a lack of suitable manure application machinery because of high purchase costs.

Critical appraisal
Although a series of policies for enhanced manure recycling have been implemented, most of these have targeted large intensive farms only. While this is understandable with an increasing proportion of livestock being reared in these intensive systems, there are still numerous less intensive livestock farms in China [42] . Another complicating factor is the lack of knowledge about typical manure composition, and best manure management practices among farmers, advisors and government officers. This also leads to imprecise definitions that are not operational in practice. For example, in China manure recycling has been defined as the fraction of manure produced by livestock that is applied to croplands, and a target of 90% manure recycling has been set for 2035. In practice, manures will be stored and treated before application and significant fractions of the nitrogen, organic carbon and water will be lost via volatilization, leaching, decomposition and evaporation. The question is then how to verify that 75% of all livestock excreta will be applied to croplands by 2020, 80% by 2025 and 90% by 2035. It is unclear whether 'manure recycling' has been defined in terms of manure volume, mass, or nitrogen or phosphorus content.
A rethink is also needed regarding the government incentives to improving manure management. Subsidies are now provided to large livestock farms to build manure stores and manure treatment facilities that result in commercial organic fertilizers. However, there are no specific measures to ensure the continued operation of treatment facilities once built, and there are too few incentives to promote the effective utilization of the manure products generated.
The main barriers against crop farmers using manures are the high costs of transportation, lack of manure application equipment, and lack of qualified labor (lack of trained/educated farmers to make the best use of manure nutrients) for manure application [19] . As a result, treatment facilities on livestock farms are often not in operation due to technical failures, high operational costs, lack of product marketing, and lack of control of product quality. And although government reports indicate that manure recycling has increased from < 60% in 2015 to 70% by the end of 2017 [71] , it remains unclear how manure recycling has been defined.

Conclusions and outlook
The livestock sector has developed very rapidly in China during the last two decades in response to the increasing demand of animal-sourced food. This development has created a manure nutrient surplus at the farm and regional levels, especially as a result of concentrations of large landless livestock farms which import feed from elsewhere. The government has strongly facilitated the modernization and intensification of the livestock sector and has also implemented a series of policies and incentives for the appropriate handling and treatment of livestock manures. However, manure management remains a major challenge. The main bottlenecks to effective manure utilization are (i) the spatial separation of large intensive landless livestock farms from the many small-holder crop farms, (ii) the lack of third-party organizations, governmental institutions and appropriate technology for transporting manure from livestock farms to crop farms, (iii) the lack of small-scale manure spreading machinery and a manure nutrient recommendation system and associated training to guide farmers and advisers on manure nutrient application to crops, and (iv) the lack of governmental incentives for the end-users to adopt the use of animal manure products.
Improved integration of crop and livestock production systems is fundamental to increasing the effective use of animal manure resources. This integration is also an important means of reducing agricultural non-point source pollution and delivering national agricultural 'green' development goals [74][75][76][77][78] . Improvement of manure recycling and effective utilization in crop production have the potential to greatly reduce the use of synthetic fertilizers, to improve soil quality and crop nutrition and maintain high yields (through the supply of organic matter and secondary nutrients and micronutrients), and to decrease the eutrophication of surface waters and ammonia and GHG emissions to the atmosphere. This, however, requires great improvements in manure management practices, and hence in government policy measures. A rethink of current policies is needed.
It is imperative to develop policies and support programs to enhance the sustainability of livestock production and manure management practices. This will require: (1) establishment of comprehensive region-specific and farm type-specific nutrient management plans, based on accurate accounts of nutrient input-output balances; (2) a partial redirection of financial support from manure producers and manure treatment industries to manure users, and from investments in treatment facilities to end-users or third-party contractors (support for operational costs); (3) an institutional framework for the effective control and transportation of manures from producers to users, involving intermediate third-party enterprises, with governmental coordination using different specialized service models; and (4) strengthening third-party service organizations (contractors) to promote manure application to croplands in an economical and environmentally sound manner. The diversity among livestock farms is very large, from smallholders with a few pigs to large farms with thousands of pigs, and very large industrial enterprises with millions of pigs. These different enterprises have their own challenges in manure management and will need to adopt different specialized service models [42] (Table 4).
Government support for the livestock sector has to be embedded into policies aimed at improving manure management based on nutrient accounting through the entire manure management chain [19,48] to ensure that all manure nutrients from intensive livestock production are properly collected, stored, and applied to arable land at appropriate rates and times and with appropriate methods. A recording system is needed, supported by government and research institutes, to assist accurate manure nutrient accounting.
Improving the performance of livestock production and manure management is an important target of the Agricultural Green Development program. With great attention and strong support of manure resource recycling program from policy, research, and farm, vast improvements can be made in the sustainability of livestock production and manure management with benefits for cropping farms, soil health and reduced negative impacts on water and air quality. Table 4 Linking crop and livestock production, as a function of livestock farm size [42] Size of livestock farm Households and small farms Medium and large farms Huge livestock company Organization modes of linking crop and livestock production Linking crop and livestock production through farmer cooperatives Linking crop and livestock production through specialized service (e.g., contractors, manure treatment center)