Research on Agricultural Carbon Emissions and Regional Carbon Emissions Reduction Strategies in China

: Carbon emissions and strategies for reducing them have become hot topics in recent years. This study ﬁrstly measured the total amount and the intensity of agricultural carbon emissions (i.e., agricultural carbon emission per capital) in China. The results show that China’s total carbon emission in 2016 was 272.022 million tons, which is 26.67% more than that in 2000, with an average annual increase of 1.67%. It then compared the regional di ﬀ erences of agricultural carbon emissions in China using the method of coe ﬃ cient of variation and the Theil index. Following this, this paper ﬁnally provides scientiﬁc and technological support for the reduction of agricultural carbon emissions in China based on a matrix of carbon emission reduction strategies.

Sustainability 2020, 12, 2627 3 of 20 The estimation of agricultural carbon emissions in China has been focused on carbon emission sources. For example, some scholars have estimated the agricultural carbon emissions based on the measurement of conversion factors of coal, oil, natural gas, and other resources used in agricultural production [20][21][22][23]. Some others have measured the carbon emissions caused by changes in the agricultural land use in some ethnic regions in China through the measurement of carbon emissions from fertilizers, pesticides, agricultural plastic films, diesel fuels, conservation tillage, and irrigation technology [10,12,14,15]. Besides, the perspective of input-output, which takes electricity consumption into consideration, has been used by some scholars to measure the agricultural carbon emissions in Chongqing [23]. Recently, further research has been undertaken on the carbon emissions of livestock and poultry, including cows, sheep, goats, pigs, chickens, and ducks [24,25].
In general, the measurement of agricultural carbon emissions has been modified a lot since it was proposed. A general research framework with differences in the selection of secondary indicators has been developed to make estimations of the carbon emissions caused by agricultural land use (or material input in agriculture) and livestock and poultry farming [18,20,22]. However, the estimation of carbon emissions from rice cultivation and soil has not been standardized [23]. Carbon emissions from rice cultivation are usually estimated by multiplying the area of rice cultivation by a given coefficient, which varies between institutions. Some institutions use coefficients with regional differences while others use the same coefficient for the whole country [21]. As for the carbon emissions from soil, they are usually estimated based on the relevant experimental data from a certain area rather than data collected nationwide. However, carbon emissions from soil can be affected greatly by cultivation methods. Therefore, the agricultural carbon emissions in this paper have been estimated without considering the carbon emissions from soil. Rice cultivation has been estimated with a coefficient that reflects both regional differences and differences in species.
Based on an input-output table, some economists have estimated the carbon emissions from direct and indirect energy consumption at each upstream production stage of agricultural inputs with the method of environmental input-output (EIO) and the method of the life cycle of agricultural production (LCA) [26]. Furthermore, scholars and institutions, such as the World Resources Institute, the World Business Council for Sustainable Development, Matthews, and II. S., have proposed the Tiered Input-Output Life Cycle Assessment (TIO-LCA) [27] to prioritize agricultural emission reduction actions. It should be noted that the existing studies on the estimation of agricultural carbon emissions were mainly conducted by comparing traditional intensive agriculture and organic agriculture. Some foreign scholars have conducted a comparative study on the environmental impact of traditional intensive agriculture and organic agriculture in Australia with the hybrid input-output life cycle method. Samples selected in the research covered different regions, species of crops, scales, and methods of cultivation as well as different growing seasons [16]. In terms of the research method, the direct carbon emissions from on-farm production activities and other environmental impacts were estimated with the method of the life cycle, indirect carbon emissions from off-farm production activities was estimated with the method of input-output, and the agricultural emission reduction actions were prioritized through analysis of the structural path [16]. This research provided a comprehensive estimation of carbon emissions throughout the agricultural production process, measured the energy consumption (including the consumption of electricity, fertilizers, pesticides, seeds, and fodder) of fruits, vegetables, and livestock products and compared the energy consumption structure of agricultural production in different regions of Australia. The results show that, although the amount of water utilization and labor input in organic agriculture is higher than that in traditional intensive agriculture, the indirect contributions of other aspects (such as energy utilization and greenhouse gas emissions) in organic agriculture are much better than those in traditional intensive agriculture. Therefore, the indirect impacts (especially in off-farm production activities) have to be taken into consideration when estimating the environmental sustainability of different farming methods.
According to the estimation of agricultural carbon emissions in the United States, about half of the carbon emissions caused by agricultural production come from the use of agricultural land, while about a Sustainability 2020, 12, 2627 4 of 20 third come from the intestinal fermentation of livestock. The proportion of agricultural carbon emissions in total carbon emissions is highly related to the agricultural practices of different countries [28]. According to the estimation of carbon emissions from different emission sources (fertilizers, energy consumption, and crop cultivation) conducted by scholars in China [29], carbon emissions from fertilizers accounted for the largest proportion of carbon emissions [30]. Carbon emissions in China have been increasing since 1995 [31], but the growth rate has declined in recent years [32]. It has been found that all the carbon emissions from farmland, carbon sequestration, and the carbon footprint in 31 provinces in China have increased. Besides, according to research conducted in Heilongjiang, the field ecosystem is the main source of carbon emissions. The research also showed a positive correlation between agricultural carbon emissions and the input of agricultural chemicals, energy consumption, and farming forms [33]. Traditional cultivation ways cause a large amount of carbon emissions. Agricultural carbon emissions can be affected by the method of land use. It has been proven that agricultural carbon emissions can be effectively reduced by afforestation and the Grain for Green Program [34]. Carbon emissions from construction land are the highest, compared with those from urban land, rural residential land, land for transportation, and agricultural land [35].
It can be seen that further research is needed into regional agricultural carbon emissions. Therefore, using the coefficient of variation and the Theil index, this paper analyzes the spatial and temporal heterogeneity of agricultural carbon emissions in different regions of China and makes policy recommendations to support the reduction of agricultural carbon emissions. The second part is method and data, the third part is the regional differences of agricultural carbon emissions, the forth part is agricultural carbon emissions per capita and intensity, the fifth part is policy recommendations for the reduction of regional agricultural carbon emissions, and the last part is conclusions and discussion.

Measure of Agricultural Carbon Emissions by Province
The data in this paper were collected from the China Rural Statistical Yearbook, the China Statistical Yearbook, and the Economy Prediction System (EPS) Database (Beijing fuqua information technology co. LTD: Beijing, China). The prices used in this paper were converted according to the price in 2000.

Carbon Emissions from Agricultural Land Use
This paper mainly estimated the agricultural carbon emissions from fertilizers, pesticides, agricultural plastic films, diesel fuel consumption, crop sowing, and irrigation. The emission factors are shown in Table 1.  [45][46][47][48] Based on these factors, the carbon emission was estimated as follows: where E is the total carbon emission caused by agricultural land use and E f e , E pe , E pl , E ga , E so , and E ir are estimated on the basis of the parameters of fertilizers, pesticides, agricultural plastic films, diesel fuel consumption, the sowing area, and the effective irrigation area. The carbon emission of rice cultivation in this paper was estimated according to the standard of the FAO. Rice cultivation can be greatly affected by climate conditions [25]. Rice is one of the most important emission sources of CH 4 . Additionally, the CH 4 emission of rice in different growth cycles can be affected by climate and hydrothermal conditions. Therefore, based on the existing calculation model of carbon emission coefficient [39], the CH 4 emission factors of rice in this paper was estimated according to the data on climate, soil, and hydrology in different provinces (see Table 2). and the greenhouse gas accounting method in China's "Guidelines for the Preparation of Provincial Greenhouse Gas Inventories (Trial)", the N 2 O in the atmosphere mainly comes from agricultural land, animal manure management, and the wastewater treatment processes of the waste treatment sector, among which more than 70% of the nitrogen emissions come from agricultural production. As this paper is about agricultural carbon emissions, N 2 O emissions have not been measured and only the CH 4 emissions have been taken into consideration) that occur during manure treatment. In this paper, we only measured the carbon emission factors of cattle, horses, donkeys, mules, pigs, goats, sheep, and poultry [32] (see Table 3). Carbon emissions from livestock and poultry in each province were estimated with the number of poultry produced in each province by the end of the year and the number of other animals kept in each province by the end of the year. Based on the methods proposed in current research [27], the number of poultry used in this paper was modified as follows: where N is the modified number of poultry, Days_alive is the growth cycle of poultry (here this equals 55), and M is the number of poultry produced in each province by the end of the year. In order to simplify the estimation, the emission of CH 4 in this paper was converted to that of standard C. According to the report issued by the IPCC, the greenhouse effect caused by 1 ton of CH 4 is equivalent to that caused by 6.82 tons of C (25 tons of CO 2 ).

Coefficient of Variation
In this paper, the changes in agricultural carbon emission per capita were reflected by the coefficient of variations.
where, X is the agricultural carbon emission per capita at the national level, X i is the agricultural carbon emission per capita of the eight economic zones, and n is the number of regions in the economic zone.
The larger the value of CV is, the greater the difference among regional agricultural carbon emissions per capita is.

Theil Index
The Theil index has been widely used in the measurement of income inequality since it was proposed. With the Theil index, the overall difference can be divided into two parts. One is brought about by regional differences, and the other is brought about by intra-regional differences. The Theil index was adopted here to explain the overall difference of agricultural carbon emissions in eight economic zones [49]. In this case, the contribution rates of regional differences and intra-regional differences to the overall agricultural carbon emissions were measured with the Theil index.
T wr % = T wr T % (8) where ACE represents the total agricultural carbon emission, GDP is the total output of the agricultural and forestry economy, GDP j is the proportion of the j-th province's GDP within the national GDP, and GDP i is the proportion of the i-th economic zone's GDP within the national GDP. ACE j is the proportion of the j-th province's agricultural carbon emissions within the national agricultural carbon emissions and ACE i is the proportion of the i-th economic zone's agricultural carbon emissions in the national agricultural carbon emissions. T is the overall difference in agricultural carbon emissions, T wr is the regional difference in agricultural carbon emissions, T br is the difference in agricultural carbon emissions within the regions, T wr % is the contribution rate of regional differences to the overall difference, and T br % is the contribution rate of differences within regions to the overall difference.

Research Area Division
Agricultural carbon emissions are different in different regions. Based on existing research [46], the research areas were divided into four parts (the eastern region, central region, western region, and northeast region) and eight economic zones (the northern coast, eastern coast, southern coast, the middle reaches of the Yangtze River, the middle reaches of the Yellow River, the northwest region, the southwest region, and the northeast region), respectively (see Figure 1), according to similarities in agricultural production activities and the possibility of regional cooperation to reduce emissions.
Sustainability 2020, 12, x; doi: FOR PEER REVIEW www.mdpi.com/journal/sustainability similarities in agricultural production activities and the possibility of regional cooperation to reduce emissions.

Overall Analysis of Agricultural Carbon Emissions
The outcomes of the measurements of agricultural carbon emissions from 2000 to 2016 are shown in Table 4.

Overall Analysis of Agricultural Carbon Emissions
The outcomes of the measurements of agricultural carbon emissions from 2000 to 2016 are shown in Table 4. In 2016, China's total carbon emissions were 272.022 million tons, which is 26.67% more than that in 2000, with an average annual increase of 1.67%. The carbon emissions caused by land use, rice planting, and livestock and poultry were 110.5649, 70.193, and 91.2642 million tons, respectively, accounting for 40.64%, 25.8%, and 33.55% of the agricultural carbon emissions, respectively.
Agricultural carbon emissions increased greatly from 2000 to 2016 in total. However, there were several fluctuations. To be specific, agricultural carbon emissions increased slowly from 2000-2003 while they increased rapidly from 2004-2006. Later, between 2006 and2008, agricultural carbon emissions declined slightly and then increased. Since then, agricultural carbon emissions have remained stable. This can be explained by the fluctuation of the rice cultivation acreage. Based on this, it was estimated that agricultural carbon emissions will continue to increase in the next few years.
As agricultural carbon emissions are susceptible to the total amount of resources in each province, the agricultural carbon emissions of 31 provinces in this paper were evaluated by the intensity of carbon emissions (ton/10,000 yuan), which refers to the agricultural carbon emissions caused by the gross agricultural output value per 10,000 yuan. It can be seen from Figure   In 2016, China's total carbon emissions were 272.022 million tons, which is 26.67% more than that in 2000, with an average annual increase of 1.67%. The carbon emissions caused by land use, rice planting, and livestock and poultry were 110.5649, 70.193, and 91.2642 million tons, respectively, accounting for 40.64%, 25.8%, and 33.55% of the agricultural carbon emissions, respectively.
Agricultural carbon emissions increased greatly from 2000 to 2016 in total. However, there were several fluctuations. To be specific, agricultural carbon emissions increased slowly from 2000-2003 while they increased rapidly from 2004-2006. Later, between 2006 and2008, agricultural carbon emissions declined slightly and then increased. Since then, agricultural carbon emissions have remained stable. This can be explained by the fluctuation of the rice cultivation acreage. Based on this, it was estimated that agricultural carbon emissions will continue to increase in the next few years.
As agricultural carbon emissions are susceptible to the total amount of resources in each province, the agricultural carbon emissions of 31 provinces in this paper were evaluated by the intensity of carbon emissions (ton/10,000 yuan), which refers to the agricultural carbon emissions caused by the gross agricultural output value per 10,000 yuan. It can be seen from Figure 2

Regional Variation of Agricultural Carbon Emissions
In terms of total agricultural carbon emissions, the central region has always ranked first, while the eastern region ranked second until 2013 when it was surpassed by the western region. Agricultural carbon emissions in the central region, western region, and the northeast region increased slowly from 2000 to 2016, while agricultural carbon emissions in the eastern region were stable from 2000-2006 and declined from 2010-2015. This was positively related to the technological and green transformation during this period.
The eight economic zones in China were roughly divided into four groups according to their agricultural carbon emissions from 2000 to 2016. The first group included the middle reaches of the Yangtze River and the southwest region. The second group was the middle reaches of the Yellow River. The third group included the northern coast and the northeast region. The fourth group included the eastern coastal economic zone, the southern coastal economic zone, and the northwest economic zone. To be specific, the middle reaches of the Yangtze River were the highest. The agricultural carbon emissions in the middle reaches of the Yangtze River and the Yellow River increased significantly, while those in the eastern coastal economic zone and the southern coastal economic zone remained stable.

Analysis of Carbon Emission Per Capita
From 2000 to 2016, the agricultural carbon emissions in four regions increased with significant differences in their trends. To be specific, carbon emissions per capita in the northeast region rose rapidly, which could be explained by the large-scale cultivation of corn. In the eastern, central, and western regions, carbon emissions per capita were highest in 2006 and then increased slowly.
From 2000 to 2016, there were great differences among agricultural carbon emissions per capita in different regions. Specifically, in 2016, agricultural carbon emissions per capita in the northeast region were 0.9986 tons, which is the highest, followed by those in the northwest region, the middle reaches of the Yangtze River, the southwest region, the northern coast, the eastern coast, and the southern coast. Emissions per capita had a positive relation with the level of economic development.
From 2000 to 2016 (see Figure 3), the intensity of agricultural carbon emissions in the four regions showed a downward trend. Moreover, agricultural carbon emissions declined rapidly from 2007-2012 and then showed a slowing rate of decline from 2013. The agricultural carbon emissions intensity in the eastern region were the lowest over the years, indicating that the carbon emissions from agricultural production in the eastern region were the lowest.

Analysis of Carbon Emission Intensity
From 2000 to 2016, the carbon emission intensity in the northwest was relatively high (Figure 4), especially in 2000. However, the intensities of all economic zones dropped significantly by the year 2016, when the intensity of carbon emissions in the northwest was the highest, followed by the middle reaches of the Yangtze River, the northeast region, the middle reaches of the Yellow River, the southwest region, the northern coast, the eastern coast, and the southern coast, indicating that the intensity of carbon emissions in Guangzhou and other regions was the lowest. In 2016, the intensity of carbon emissions in Tibet ranked first, which was 3.93 tons/10,000 yuan, while the intensity of carbon emissions in Fujian was only 0.63 tons/10,000 yuan which was the lowest.
Except for Tibet, Qinghai, and Xinjiang, the agricultural carbon emissions in other provinces caused by agricultural land use all increased. According to the main source of the carbon emissions,

Analysis of Carbon Emission Intensity
From 2000 to 2016, the carbon emission intensity in the northwest was relatively high (Figure 4), especially in 2000. However, the intensities of all economic zones dropped significantly by the year 2016, when the intensity of carbon emissions in the northwest was the highest, followed by the middle reaches of the Yangtze River, the northeast region, the middle reaches of the Yellow River, the southwest region, the northern coast, the eastern coast, and the southern coast, indicating that the intensity of carbon emissions in Guangzhou and other regions was the lowest.

Analysis of Carbon Emission Intensity
From 2000 to 2016, the carbon emission intensity in the northwest was relatively high (Figure 4), especially in 2000. However, the intensities of all economic zones dropped significantly by the year 2016, when the intensity of carbon emissions in the northwest was the highest, followed by the middle reaches of the Yangtze River, the northeast region, the middle reaches of the Yellow River, the southwest region, the northern coast, the eastern coast, and the southern coast, indicating that the intensity of carbon emissions in Guangzhou and other regions was the lowest.  In 2016, the intensity of carbon emissions in Tibet ranked first, which was 3.93 tons/10,000 yuan, while the intensity of carbon emissions in Fujian was only 0.63 tons/10,000 yuan which was the lowest.
Except for Tibet, Qinghai, and Xinjiang, the agricultural carbon emissions in other provinces caused by agricultural land use all increased. According to the main source of the carbon emissions, these provinces can be divided into five groups: land-use-dominated regions (the agricultural carbon emissions were mainly caused by agricultural activities), rice-cultivation-dominated regions (the agricultural carbon emissions were mainly caused by rice cultivation), livestock-and-poultry-farming-dominated regions (the agricultural carbon emissions were mainly caused by livestock and poultry farming), compound-factor-dominated regions (the agricultural carbon emissions were mainly caused by agricultural land use and rice cultivation, rice cultivation and livestock and poultry farming, agricultural land use and livestock and poultry farming, and the carbon emissions from other factors only accounted for a small proportion, usually below 20%), and balanced regions.
From 2000 to 2016, carbon emissions caused by the use of agricultural land increased year by year. Crop planting was the main agricultural activity in these regions, while livestock and poultry farming and rice cultivation only accounted for a tiny percentage of their agricultural activities. With the implementation of China's rural revitalization strategy, especially the development of green agriculture and forestry industry, agricultural carbon emissions will gradually decline.

Variation of Regional Agricultural Carbon Emissions
T represents the overall differences in carbon emissions, T br represents the intra-regional differences in carbon emissions, and T br represents the regional differences in carbon emissions.
The three indices changed to some extent during the observation period (Table 5). Hence, the fluctuation of regional differences was relatively smooth. The changes of the Theil index were caused by intra-regional differences, which were greater than regional differences. It was found that there were some rules for the increases in regional differences of agricultural carbon emissions in the eight economic zones, which can be explained by the intra-regional differences.  Figure 5 shows the Theil index of overall differences of agricultural carbon emissions in eight economic zones from 2000 to 2016. It can be seen that the Theil index in the middle reaches of the Yangtze River was relatively stable, while that in the south coastal economic zone increased gradually, indicating that the overall differences in agricultural carbon emissions increased. Moreover, the Theil index in the southwest region and the south coast also increased, while those in the other economic zones had few changes for many years. economic zones, which can be explained by the intra-regional differences. Figure 5 shows the Theil index of overall differences of agricultural carbon emissions in eight economic zones from 2000 to 2016. It can be seen that the Theil index in the middle reaches of the Yangtze River was relatively stable, while that in the south coastal economic zone increased gradually, indicating that the overall differences in agricultural carbon emissions increased. Moreover, the Theil index in the southwest region and the south coast also increased, while those in the other economic zones had few changes for many years. The intra-regional differences of agricultural carbon emissions from 2000-2016 are summarized as follows:

The Theil Index in Eight Economic Zones
The intra-regional differences of agricultural carbon emissions in the northern coastal region were relatively stable, with slight fluctuations in 2006 and 2009. It was generally stable, especially from 2009 to 2015, and then increased from 2016. The intra-regional differences of agricultural carbon emissions in the eastern coastal region declined gradually, and became the lowest among the eight economic zones from 2009. The trend of intra-regional differences of agricultural carbon emissions in the southern coastal region was consistent with that of the eastern coastal region, but with a lower speed. The peak of the intra-regional difference of agricultural carbon emissions in the middle reaches of the Yellow River appeared in 2008. The differences declined in 2019 and showed an upward trend from 2009 to 2016. The intra-regional differences of agricultural carbon emissions in the middle reaches of the Yangtze River were always the largest, and there was a sight fluctuation from 2006-2007. The intra-regional differences of agricultural carbon emissions in the southwest region increased from 2000 to 2005 and from 2008 to 2016, while they declined from 2005 to 2007. The intraregional differences of agricultural carbon emissions in the northwest region and the northeast region from 2000 to 2016 were relatively stable. Figure 6 shows radar charts of the changes of agricultural carbon emissions per capita in the eight economic zones in different years, measured by the variation coefficient method. The intra-regional differences of agricultural carbon emissions from 2000-2016 are summarized as follows: The intra-regional differences of agricultural carbon emissions in the northern coastal region were relatively stable, with slight fluctuations in 2006 and 2009. It was generally stable, especially from 2009 to 2015, and then increased from 2016. The intra-regional differences of agricultural carbon emissions in the eastern coastal region declined gradually, and became the lowest among the eight economic zones from 2009. The trend of intra-regional differences of agricultural carbon emissions in the southern coastal region was consistent with that of the eastern coastal region, but with a lower speed. The peak of the intra-regional difference of agricultural carbon emissions in the middle reaches of the Yellow River appeared in 2008. The differences declined in 2019 and showed an upward trend from 2009 to 2016. The intra-regional differences of agricultural carbon emissions in the middle reaches of the Yangtze River were always the largest, and there was a sight fluctuation from 2006-2007. The intra-regional differences of agricultural carbon emissions in the southwest region increased from 2000 to 2005 and from 2008 to 2016, while they declined from 2005 to 2007. The intra-regional differences of agricultural carbon emissions in the northwest region and the northeast region from 2000 to 2016 were relatively stable. Figure 6 shows radar charts of the changes of agricultural carbon emissions per capita in the eight economic zones in different years, measured by the variation coefficient method.
Generally, the agricultural carbon emissions per capita in the eight economic zones all showed an uptrend from 2000 to 2016. According to the circle layers of the radar charts, the regions in outer layers have higher agricultural carbon emissions per capita. It can be seen from Figure 6   Generally, the agricultural carbon emissions per capita in the eight economic zones all showed an uptrend from 2000 to 2016. According to the circle layers of the radar charts, the regions in outer layers have higher agricultural carbon emissions per capita. It can be seen from Figure 6 that in 2000 and 2015 the agricultural carbon emissions per capita in the northeast economic zone and the northwest economic zone were the highest, while in 2010 and 2016, the agricultural carbon emissions per capita in the northeast economic zone were the highest.

Policy Recommendations for the Reduction of Regional Agricultural Carbon Emissions
Based on the above research, this paper has constructed a matrix of total carbon emissions and the intensity of carbon emissions to analyze the regional policies for the reduction of agricultural carbon emissions in eight economic zones. The design of regional policy is a comprehensive and complex science, which needs classified considerations to ensure the pertinence of policy implementation.
The classified policy for the reduction of carbon emissions are important parts of China's national carbon emissions reduction policy. The classification of the intensity of carbon emissions and total agricultural carbon emissions are shown in Table 6. Table 6. Classification of the intensity of carbon emissions and total agricultural carbon emissions.

Policy Recommendations for the Reduction of Regional Agricultural Carbon Emissions
Based on the above research, this paper has constructed a matrix of total carbon emissions and the intensity of carbon emissions to analyze the regional policies for the reduction of agricultural carbon emissions in eight economic zones. The design of regional policy is a comprehensive and complex science, which needs classified considerations to ensure the pertinence of policy implementation.
The classified policy for the reduction of carbon emissions are important parts of China's national carbon emissions reduction policy. The classification of the intensity of carbon emissions and total agricultural carbon emissions are shown in Table 6. Table 6. Classification of the intensity of carbon emissions and total agricultural carbon emissions. Therefore, there are nine types of combinations of emission and intensity, including low emission and low intensity (LE&LI), low emission and medium intensity (LE&MI), low emission and high intensity (LE&HI), medium emission and low intensity (ME&LI), medium emission and medium intensity (ME&MI), medium emission and high intensity (ME&HI); high emission and low intensity (HE&LI), high emission and medium intensity (HE&MI), high emission and high intensity (HE&HI). Agricultural production and livestock products are good outputs, while agricultural carbon emissions are bad outputs. The lower the intensity of agricultural carbon emissions is, the lower the carbon emissions of agricultural production per unit are. Therefore, low emission and low intensity (LE&LI) tends to be the best combination (Table 7).

Regional Division
Based on the concept of coordinated development in the eight economic zones, this paper proposes that corresponding policies for the reduction of agricultural carbon emissions should be adopted for different economic zones. --ME&MI; --ME&LI; LE&MI; --LE&LI ept of coordinated development in the eight economic zones, this paper nding policies for the reduction of agricultural carbon emissions should be onomic zones.

ment in the Northern Coastal Economic Zone
tal economic zone includes the two cities of Beijing and Tianjin and the two Shandong. The two provinces are important bases of agricultural production ndong province, which is also an important base of vegetable production in ong also plays an important role in the development of modern agriculture. characterized by a high level of openness and well-developed science and ortation conditions. However, the integration process in this region is ricultural products mainly support the Beijing area, which has hindered the eration mechanism of carbon emission reduction among different provinces. rbon emissions in the northern coastal economic zone should be reduced and ural carbon emissions should be controlled. Since leisure agriculture and he suburbs of Beijing have been developed, Hebei and Shandong provinces agement technologies and methods to promote agricultural transformation. Province, as the largest exporter of agricultural products in China, should ation of high-end and high value-added industries so as to realize the rading of industrial structure.

ment in the Eastern Coastal Economic Zone
f the eastern coastal economic zone, which includes the city of Shanghai and ngsu and Zhejiang, has been promoted by China's reform and opening-up y become the center of China's modern industries. With 40 years of reform odern financial system in this region has been formed, and its agricultural ready relatively high. cultural carbon emissions in this region should be reduced moderately. The g industry can be a strong driving force for the development of agriculture in also be accelerated by increasing the proportion of the tertiary industry; lopment of logistics, consulting, and other industries as well as increasing the region. --ME&MI; --ME&LI; LE&MI; --LE&LI pt of coordinated development in the eight economic zones, this paper ing policies for the reduction of agricultural carbon emissions should be omic zones.

ent in the Northern Coastal Economic Zone
economic zone includes the two cities of Beijing and Tianjin and the two andong. The two provinces are important bases of agricultural production dong province, which is also an important base of vegetable production in ng also plays an important role in the development of modern agriculture. haracterized by a high level of openness and well-developed science and rtation conditions. However, the integration process in this region is cultural products mainly support the Beijing area, which has hindered the ation mechanism of carbon emission reduction among different provinces. on emissions in the northern coastal economic zone should be reduced and al carbon emissions should be controlled. Since leisure agriculture and suburbs of Beijing have been developed, Hebei and Shandong provinces ement technologies and methods to promote agricultural transformation. rovince, as the largest exporter of agricultural products in China, should tion of high-end and high value-added industries so as to realize the ding of industrial structure.

ent in the Eastern Coastal Economic Zone
the eastern coastal economic zone, which includes the city of Shanghai and gsu and Zhejiang, has been promoted by China's reform and opening-up become the center of China's modern industries. With 40 years of reform ern financial system in this region has been formed, and its agricultural ady relatively high. ltural carbon emissions in this region should be reduced moderately. The industry can be a strong driving force for the development of agriculture in lso be accelerated by increasing the proportion of the tertiary industry; pment of logistics, consulting, and other industries as well as increasing he region. Based on the concept of coordinated development in the eight eco proposes that corresponding policies for the reduction of agricultural ca adopted for different economic zones.

Agricultural Development in the Northern Coastal Economic Zone
The northern coastal economic zone includes the two cities of Beijing provinces of Hebei and Shandong. The two provinces are important bases in China, especially Shandong province, which is also an important base o China. Moreover, Shandong also plays an important role in the developme This region is generally characterized by a high level of openness and w technology and transportation conditions. However, the integration p relatively slow as its agricultural products mainly support the Beijing are establishment of a cooperation mechanism of carbon emission reduction a The agricultural carbon emissions in the northern coastal economic zo its intensity of agricultural carbon emissions should be controlled. Sinc picking agriculture in the suburbs of Beijing have been developed, Hebei can learn from its management technologies and methods to promote ag Furthermore, Shandong Province, as the largest exporter of agricultural p focus on the transformation of high-end and high value-added indus transformation and upgrading of industrial structure.

Agricultural Development in the Eastern Coastal Economic Zone
The development of the eastern coastal economic zone, which include the two provinces of Jiangsu and Zhejiang, has been promoted by China policy, and it has already become the center of China's modern industries and opening up, the modern financial system in this region has been for input and output are already relatively high.
Therefore, the agricultural carbon emissions in this region should be high-end manufacturing industry can be a strong driving force for the dev this region, which can also be accelerated by increasing the proportion strengthening the development of logistics, consulting, and other indust brand awareness within the region.

Agricultural Development in the Southern Coastal Economic Zone
The southern coastal economic zone covers the city of Guangzhou Based on the concept of coordinated development in the eight econom proposes that corresponding policies for the reduction of agricultural carbon adopted for different economic zones.

Agricultural Development in the Northern Coastal Economic Zone
The northern coastal economic zone includes the two cities of Beijing an provinces of Hebei and Shandong. The two provinces are important bases of ag in China, especially Shandong province, which is also an important base of ve China. Moreover, Shandong also plays an important role in the development o This region is generally characterized by a high level of openness and well-d technology and transportation conditions. However, the integration proc relatively slow as its agricultural products mainly support the Beijing area, w establishment of a cooperation mechanism of carbon emission reduction amon The agricultural carbon emissions in the northern coastal economic zone s its intensity of agricultural carbon emissions should be controlled. Since le picking agriculture in the suburbs of Beijing have been developed, Hebei and can learn from its management technologies and methods to promote agricu Furthermore, Shandong Province, as the largest exporter of agricultural prod focus on the transformation of high-end and high value-added industries transformation and upgrading of industrial structure.

Agricultural Development in the Eastern Coastal Economic Zone
The development of the eastern coastal economic zone, which includes th the two provinces of Jiangsu and Zhejiang, has been promoted by China's re policy, and it has already become the center of China's modern industries. W and opening up, the modern financial system in this region has been formed input and output are already relatively high.
Therefore, the agricultural carbon emissions in this region should be red high-end manufacturing industry can be a strong driving force for the develop this region, which can also be accelerated by increasing the proportion of strengthening the development of logistics, consulting, and other industries brand awareness within the region.

Agricultural Development in the Southern Coastal Economic Zone
The southern coastal economic zone covers the city of Guangzhou and Based on the concept of coordinated development in the eight economi proposes that corresponding policies for the reduction of agricultural carbon e adopted for different economic zones.

Agricultural Development in the Northern Coastal Economic Zone
The northern coastal economic zone includes the two cities of Beijing and provinces of Hebei and Shandong. The two provinces are important bases of agr in China, especially Shandong province, which is also an important base of veg China. Moreover, Shandong also plays an important role in the development of This region is generally characterized by a high level of openness and well-dev technology and transportation conditions. However, the integration proces relatively slow as its agricultural products mainly support the Beijing area, whi establishment of a cooperation mechanism of carbon emission reduction among The agricultural carbon emissions in the northern coastal economic zone sho its intensity of agricultural carbon emissions should be controlled. Since leis picking agriculture in the suburbs of Beijing have been developed, Hebei and S can learn from its management technologies and methods to promote agricult Furthermore, Shandong Province, as the largest exporter of agricultural produ focus on the transformation of high-end and high value-added industries s transformation and upgrading of industrial structure.

Agricultural Development in the Eastern Coastal Economic Zone
The development of the eastern coastal economic zone, which includes the c the two provinces of Jiangsu and Zhejiang, has been promoted by China's refo policy, and it has already become the center of China's modern industries. With and opening up, the modern financial system in this region has been formed, input and output are already relatively high.
Therefore, the agricultural carbon emissions in this region should be reduc high-end manufacturing industry can be a strong driving force for the developm this region, which can also be accelerated by increasing the proportion of th strengthening the development of logistics, consulting, and other industries a brand awareness within the region.

Agricultural Development in the Southern Coastal Economic Zone
The southern coastal economic zone covers the city of Guangzhou and th y a high level of openness and well-developed science and ons. However, the integration process in this region is cts mainly support the Beijing area, which has hindered the m of carbon emission reduction among different provinces. the northern coastal economic zone should be reduced and ssions should be controlled. Since leisure agriculture and ijing have been developed, Hebei and Shandong provinces ogies and methods to promote agricultural transformation. e largest exporter of agricultural products in China, should nd and high value-added industries so as to realize the rial structure.
n Coastal Economic Zone stal economic zone, which includes the city of Shanghai and ng, has been promoted by China's reform and opening-up nter of China's modern industries. With 40 years of reform system in this region has been formed, and its agricultural igh. missions in this region should be reduced moderately. The a strong driving force for the development of agriculture in ted by increasing the proportion of the tertiary industry; tics, consulting, and other industries as well as increasing ern Coastal Economic Zone -LE&LI

Agricultural Development in the Northern Coastal Economic Zone
The northern coastal economic zone includes the two cities of Beijing and Tianjin and the two provinces of Hebei and Shandong. The two provinces are important bases of agricultural production in China, especially Shandong province, which is also an important base of vegetable production in China. Moreover, Shandong also plays an important role in the development of modern agriculture. This region is generally characterized by a high level of openness and well-developed science and technology and transportation conditions. However, the integration process in this region is relatively slow as its agricultural products mainly support the Beijing area, which has hindered the establishment of a cooperation mechanism of carbon emission reduction among different provinces.
The agricultural carbon emissions in the northern coastal economic zone should be reduced and its intensity of agricultural carbon emissions should be controlled. Since leisure agriculture and picking agriculture in the suburbs of Beijing have been developed, Hebei and Shandong provinces can learn from its management technologies and methods to promote agricultural transformation. Furthermore, Shandong Province, as the largest exporter of agricultural products in China, should focus on the transformation of high-end and high value-added industries so as to realize the transformation and upgrading of industrial structure.

Agricultural Development in the Eastern Coastal Economic Zone
The development of the eastern coastal economic zone, which includes the city of Shanghai and the two provinces of Jiangsu and Zhejiang, has been promoted by China's reform and opening-up policy, and it has already become the center of China's modern industries. With 40 years of reform and opening up, the modern financial system in this region has been formed, and its agricultural input and output are already relatively high.
Therefore, the agricultural carbon emissions in this region should be reduced moderately. The high-end manufacturing industry can be a strong driving force for the development of agriculture in this region, which can also be accelerated by increasing the proportion of the tertiary industry; strengthening the development of logistics, consulting, and other industries as well as increasing brand awareness within the region.

Agricultural Development in the Southern Coastal Economic Zone
The southern coastal economic zone covers the city of Guangzhou and the two provinces of Fujian and Hainan. With a high level of opening up due to its location near to Hong Kong (HK), Macau, and Taiwan, advanced foreign technologies are usually adopted firstly in this region, and it is also the main production base of consumer durable goods (such as cotton cloth). The main disadvantages in this region are the environmental pollution and the relatively high cost of pollution treatment.
The total amount and intensity of carbon emissions in this region should be maintained at the current level. As the center of foreign trade in China, the transformation and upgrade of the traditional processing industry can be promoted by making full use of the regional capital market-importing foreign capital, introducing advanced experience, improving the existing industrial development system, and enhancing the role of the value added by the regional wholesale market.

Agricultural Development in the Middle Reaches of the Yellow River Economic Zone
The middle reaches of the Yellow River economic zone includes the autonomous region of Inner Mongolia and the provinces of Shanxi, Shaanxi, and Henan, which are all important inland provinces in China. The pattern and level of economic development in this region are significantly different from those in the three economic zones mentioned above. The natural resources in this region are relatively rich, but the ecological environment has been greatly affected by long-term extensive cultivation. With a low agricultural output and insufficient level of opening up in this region, this region has faced great pressure to upgrade the industrial structure.
Therefore, active measures should be taken to reduce the total amount and intensity of carbon emissions in this region. With the improvement of production efficiency and the introduction of advanced technologies, the agricultural industry chain can be extended at the same time by enhancing regional and intra-regional cooperation, making full use of agricultural raw materials, such as edible fungi, and establishing a national logistics transportation network.

Agricultural Development in the Middle Reaches of the Yangtze River Economic Zone
The middle reaches of the Yangtze River economic zone includes the provinces of Hubei, Hunan, Jiangxi, and Anhui. With sufficient water sources and a large population, this region has developed a relatively mature agricultural system. However, its degree of opening up needs to be further improved, and its agricultural industrial structure should be upgraded.
For this region, moderate measures should be taken to reduce the total amount and intensity of agricultural carbon emissions. As the agricultural carbon emissions in this region are the highest in China, the proportion of high-tech industries can be increased by introducing the concept of large-scale agriculture, with emphasis on the development of leisure agriculture, agricultural tourism, and the transformation of agricultural products, so as to fully develop the modern agriculture in this region.

Agricultural Development in the Southwest Economic Zone
The southwest economic zone includes the city of Chongqing; the provinces of Yunnan, Guizhou, Sichuan, and others; and the autonomous region of Guangxi. Restricted by geographical factors, the scale of agriculture in this region tends to be small, and the quality of soil is relatively poor. However, the forestry in this region has been well developed, which provides a good foundation for the development of tourism.
Therefore, the agricultural carbon emissions should be reduced moderately and the intensity of carbon emissions should be controlled. The degree of agricultural modernization in this region can be improved by enhancing the management of agricultural production and introducing modern agricultural industry systems, such as a picking industry.

Agricultural Development in the Northwest Economic Zone
The northwest economic zone includes the provinces of Gansu and Qinghai, and the autonomous regions of Ningxia, Tibet, and Xinjiang. This region is not only the largest base of deep processing for cotton, grain, and oil products but also an important energy base in China. The production of the primary industry accounts for a large proportion of the gross production in this region, and the conditions for agricultural development are relatively poor.
Therefore, the total amount and intensity of agricultural carbon emissions in this region should be maintained at the current level. Due to the strong light throughout the year, the proportion of fruit products in the agricultural market can be gradually increased with the overall agricultural carbon emissions unchanged, and industrial upgrading can be promoted by cotton production.

Agricultural Development in Northeast Economic Zone
The northeast economic zone, which includes Liaoning, Jilin, and Heilongjiang provinces, is characterized by good agricultural production conditions. In recent years, this region has faced the pressure of depleting resources and industrial structure upgrading.
The total agricultural carbon emissions in this region should be reduced moderately and the intensity should be controlled. Furthermore, with the experiences of resource transformation at home and abroad, taking the opportunity of establishing a national carbon emission market and the rich carbon storage in this region, the management and maintenance of agricultural land can be enhanced and the area of forestry can be increased.

Conclusions and Discussion
This paper measured the agricultural carbon emissions in China, and compared the regional differences of agricultural carbon emissions using the method of coefficient of variation and the Theil index by taking four regions and eight economic zones as research areas. The results showed that, in 2016, China's total carbon emissions were 272.022 million tons, which is 26.67% more than that in 2000, and the average annual increase was 1.67%. Among them, carbon emissions caused by agricultural land use, rice cultivation, and livestock and poultry were 110.5649 million tons, 70.193 million tons, and 91.2642 million tons, respectively, accounting for 40.64%, 25.8%, and 33.55% of agricultural carbon emissions. The total agricultural carbon emissions of the three aspects mentioned above all increased from 2000 to 2016. To be specific, carbon emissions from agricultural land use increased the fastest, from 73.9473 million tons to 110.5649 million tons, with an average annual increase of 3.09%. That means the increase of agricultural output in China depends greatly on the increase of agricultural material input. There were great fluctuations in the carbon emissions from rice cultivation, which increased slightly from 69.  [32], in China, the intensity of agricultural carbon emissions declined from the west to the east (Figure 3), and in 2016, the intensity of agricultural carbon emissions showed a trend of northwest region > middle reaches the Yangtze River > northeast region > southwest region > northern Coast > eastern coast > southern coast, which is of strong similarity to previous literature.
Agricultural carbon emissions caused by straw burning and N 2 O were not taken into consideration in this paper, as existing researches have shown different results for carbon emissions caused by N 2 O. The regional differences of agricultural carbon emissions in this paper were only estimated on the basis of total carbon emissions and the intensity of carbon emissions. However, the efficiency of carbon emissions is also a very important indicator, which should be considered in further research.