中国生态农业学报(中英文)

Low carbon development strategy for agriculture based on cybernetics

LUO Shiming

2022, 30(4): 495-499. doi: 10.12357/cjea.20210583

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Agriculture is an agroecosystem with a cybernetic system nature. The low-carbon development of agriculture falls into the category of eco-friendly eco-agriculture. Human direct regulation methods for the low-carbon development of eco-agriculture originate from the exploration of traditional and local farmers, modern interdisciplinary agricultural research, and eco-friendly high-tech industries. To get low-carbon goals, the methods from different sources, which are conducive to adapting and strengthening the natural regulation process, can be investigated for their compatibility, synergy and effectiveness within a specific system. The selected methods can be synthesized and optimized to help form a diversified low-carbon system and a suitable technical package. The top-down stimulation measures introduced by the government and the bottom-up efforts provided by people constitute the human indirect regulation for agroecosystems. These entities need to cooperate to form a social joint force to effectively accelerate the low-carbon development of eco-agriculture to reach the national goal of carbon neutralization.

Mitigation of greenhouse gas emissions in China’s agricultural sector: Current status and future perspectives

LIN Bin, XU Meng, WANG Xiaoxi

2022, 30(4): 500-515. doi: 10.12357/cjea.20210843

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Reduction of greenhouse gas (GHG) emissions in China’s agricultural sector is essential to achieving carbon neutrality by 2060. China has been promoting the green transformation of its agricultural sector. This study systematically reviewed the policies and researches that are related to the reduction of GHG emissions in China’s agricultural sector, and established a governance framework for guiding future research that focuses on emission reduction in agriculture. Our results showed that China’s agriculture-related policies have already covered the main aspects of GHG emission reduction and carbon sequestration in the agricultural sector; however, technological innovation and resource use efficiency improvements should be further endorsed along with explicit policy targets. Among the existing literature, researches have focused on the estimation of agricultural GHG emissions to impact the evaluation of specific policies and measures. Future research on the improvement of agricultural GHG emission accounting and integrated assessment of emission reduction measures is needed. A governance framework for mitigating GHG emissions in agriculture has been identified in China, in which the government, market, and social organizations are the main governance entities, and the farmers are the implementation entities. Hence, to encourage farmers to reduce GHG emissions, the interactions between governmental entities and implementation entities should be considered when designing effective policies. This study summarized the current status of policies and research that are related to the mitigation of China’s agricultural GHG emissions and provided future perspectives on policy design and research foci.

Basic path and system construction of agricultural green and low-carbon development with respect to the strategic target of carbon peak and carbon neutrality

WANG Xueting, ZHANG Junbiao

2022, 30(4): 516-526. doi: 10.12357/cjea.20210772

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Achieving the targets of carbon peak and carbon neutrality is a major stratege at present and in the future in China. Agriculture is not only an important source of greenhouse gas emissions but also a huge carbon sink system. The agricultural green and low-carbon development is an important area that must be considered with respect to the target of carbon peak and carbon neutrality. Reduced agricultural carbon emissions and carbon sequestration are not only important ways to combat carbon peak, but also offer great potential. Therefore, this study examined the current situation of green and low-carbon agricultural development. At present, the total amount of agricultural carbon emissions in China has tended to stabilize and peaked, and the proportion of carbon emissions generated by the use of modern agricultural input elements, such as fertilizers and farm energy, has increased. The agricultural ecosystems is a powerful carbon sink. In this study, the main problems of agricultural green and low-carbon development were analyzed, including excessive agricultural inputs and excessive consumption of fossil energy, low utilization of agricultural resources, insufficient technical reserves for agricultural green and low-carbon development, and imperfect supporting systems. This study advocated the basic paths and measures to realizing agricultural green and low-carbon development by strengthening the conservation and utilization of agricultural resources, improving the efficiency of resource utilization, increasing the comprehensive treatment of agricultural non-point source pollution, and ensuring the reduction and efficiency of fertilizers and resource utilization of agricultural wastes. Effective control of agricultural white pollution; cultivation, expansion, and strengthening of agricultural green and low-carbon industries; realization of the greening of the entire industrial chain of agricultural products from production and processing to circulation; increase in scientific and technological innovation; and building of a scientific and technological support system for agricultural green and low-carbon development are also important ways. Finally, an institutional system that promotes agricultural green and low-carbon development is constructed from the aspects of fiscal and taxation systems, financial systems, land management systems, ecological product value realization mechanisms, and constraint and incentive mechanisms. Based on this study, agricultural green and low-carbon development policies and measures can be developed and research can be conducted.

Technical pathways of mitigating greenhouse gases emission from agriculture and rural areas under double-carbon strategy

XIE Liyong, YANG Yurong, ZHAO Hongliang, GUO Liping, JIN Zequn, YANG Yang, HE Yutong

2022, 30(4): 527-534. doi: 10.12357/cjea.20210599

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Achieving carbon peak and carbon neutrality is an extensive and profound systematic economic and social development change. This is related to the sustainable development of the Chinese nation and the construction of a community with a shared future for mankind. To achieve the strategic objectives of carbon peak and carbon neutrality, this study clarified that it is important to adjust energy structure vigorously, promote clean and low-carbon development of energy systems, accelerate the transformation of industrial structure, eliminate backward production capacity, strive to improve energy utilization efficiency, and strictly control energy consumption intensity. It is not only the objective demand of human beings to deal with climate change but also a practical demand for the transformation and upgrading of domestic industries. It is necessary to transform high energy consumption and pollution process to a high-quality development model and green and low-carbon economy, to achieve sustainable economic and social development. With the development of modern agriculture and promotion of agricultural modernization, agriculture and rural areas have shown great potential in greenhouse gas (GHG) emission reduction. Therefore, the relationship between agricultural and rural GHG sources and sinks and emission reduction potential was analyzed, and the main GHG emission sources, such as farmland systems, animal husbandry systems, waste, and daily life, were arranged in a certain order. Emissions of non-CO₂ GHGs were the focus of emission, and the emissions were relatively stable. The main emission reduction paths in agriculture and rural areas were summarized in the following order: farmland system emission reduction, animal husbandry system emission reduction, secondary resource emission reduction, and green life emission reduction. Among them, methane emission reduction in rice fields, nitrous oxide emission reduction in dry land, and methane emission reduction by ruminants are notable. The underlying scientific mechanism of emission reduction in agriculture and rural areas was discussed. Therefore, we advocated that the particularity and scientificity of emission reduction potential and internal demand of agricultural and rural development be followed, suggested that emission reduction and extreme emission reduction be paid attention to, and opposed the simple pursuit of carbon neutrality in agricultural and rural systems. We suggested that scientific and technological innovations and promotions be carried out. We strongly suggested that emission reduction and sink increase in agriculture and rural areas be carried out, guaranteeing food safety and security, co-promoting green development, pollution reduction, and carbon mitigation in agriculture, coordinating climate change adaptation, establishing innovation. Eventually, these practices would result in coordinated development of production, life, and ecology and provided support for the construction of ecological civilization and rural revitalization.

Carbon emissions of agrifood systems from energy consumption in China

ZHANG Xiangyang, ZHANG Yumei, FENG Xiaolong, FAN Shenggen, CHEN Kevin

2022, 30(4): 535-542. doi: 10.12357/cjea.20210784

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Energy consumption and carbon emissions from all sectors have increased over the past four decades. Climate change caused by carbon emissions from energy activities poses a serious risk to humans. Although carbon emissions from the direct energy consumption of agriculture are limited, agricultural production modes and consumption patterns are undergoing significant changes. The extension of the supply chain has resulted in an increase in energy consumption and carbon emissions. To estimate the carbon emissions from agrifood systems, this study used the input-output tables from 1997 to 2018 and the data of energy consumption by sector in China to estimate the carbon emissions and analyze its trends, components, and characteristics based on the input-output model. The most prominent advantage of this model is that it not only captures the carbon emissions from direct energy use, but also includes the carbon emissions from indirect energy use due to the production of intermediate inputs. This study had several findings. First, with China’s economic development, total energy consumption increased 2.2 times from 1.5 billion tons in 2000 to 4.7 billion tons of standard coal in 2018. The energy consumption of the agriculture and food processing industry has increased from 42.3 million tons and 39.2 million tons of standard coal in 2000 to 87.8 million tons and 75.1 million tons of standard coal in 2018, respectively. Second, carbon emissions from energy use in agrifood systems and non-agrifood systems have increased from 530.0 million tons and 2.7 billion tons in 1997 to 670.0 million and 9.7 billion tons in 2018, respectively. However, the growth rate of agrifood systems (1.1%) was much lower than that of non-agrifood systems (6.3%); therefore, the share of agrifood systems in the total carbon emissions from energy use declined from 16.3% in 1997 to 6.4% in 2018. Third, the food processing industry’s carbon emissions have increased significantly and have become the most important carbon emission source in agrifood systems, with 420.0 million tons accounting for 62.7% of the carbon emissions from energy activities in the agrifood systems in 2018. Carbon emissions from agriculture-related transportation and storage, wholesale and retail, and catering have continued to rise. In 2018, the total carbon emissions were 73.58 million tons, contributing to 11.1% of the carbon emissions of the energy activities in the agrifood systems. The carbon emissions from agricultural energy use showed a downward trend owing to the improvement in energy efficiency; however, this was still the second largest carbon emission source. The carbon emissions in 2018 were 170 million tons, accounting for 26.2% of the carbon emissions from energy activities in agrifood systems. Based on these results, policy suggestions are provided, such as reducing emissions from the supply chain, accelerating the development of low carbon emissions and low energy consumption in the food processing industry, promoting agricultural green development, and optimizing the energy structure to help to reduce carbon emissions.

Structure and driving factors of spatial correlation network of agricultural carbon emission efficiency in China

SHANG Jie, JI Xueqiang, SHI Rui, ZHU Meirong

2022, 30(4): 543-557. doi: 10.12357/cjea.20210607

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The study of agricultural carbon emission efficiency is important for the realization of agricultural carbon peak and carbon neutrality goals. There is a lack of studies on agricultural carbon emission efficiency based on relational data and network perspectives. These limitations restrict the development of regional agricultural collaborative emissions reduction activities. Therefore, based on relational data and network perspective, taking the development of the agricultural carbon emission efficiency of 31 provinces (cities and autonomous regions) from 2010 to 2019 as the research subject, the study used the SBM-Undesirable model to measure the efficiency of agricultural carbon emissions, constructed a modified gravity matrix of spatial correlation network of agricultural carbon emission efficiency, analyzed the structural characteristics of the spatial correlation network by applying the social network analysis method, and finally explored the driving factors through a quadratic assignment procedure (QAP) model. There are several main findings. First, despite the wide disparity across the 31 provinces (cities, autonomous regions) in China, agricultural carbon emission efficiency increased rapidly, from 0.400 to 0.756, increasing 88.8% with a creation room for improvement. Second, the network relevance of agricultural carbon emission efficiency in the provinces (cities, autonomous regions) was enhanced. For the spatial correlation networks of agricultural carbon emission efficiency in the 31 provinces (cities, autonomous regions) of China, the number of network relations increased from 121 to 211, and the network density increased from 0.130 to 0.227, while network ranking declined from 0.458 to 0.293, followed by network efficiency, which declined from 0.837 to 0.692. In addition, the spatial correlation network of agricultural carbon emission efficiency among the 31 provinces (cities, autonomous regions) had formed multiple network centers that played an important role in controlling agricultural carbon emission efficiency. Overall, the eastern coastal areas were the main destinations for cyberspace space-related spillover of agricultural carbon emission efficiency in 31 provinces (cities and autonomous regions) in China. Third, the transport-level difference, resident income difference, difference in the output value of the first industry and information-level difference had an important impact on the formation of a spatial correlation network of agricultural carbon emission efficiency in China. Finally, the study findings demonstrated that the differences in transportation level and the output value of the primary industry significantly promoted spatial correlation network development. Similarly, it was found that per capita income, information level, and spatial distance also emphasized spatial correlation network formation. Based on the research conclusions, we proposed some suggestions for enhancing the spatial correlation of agricultural carbon emission efficiency, such as emphasizing the development of inter-regional coordinated emission reduction activities and differences of various provinces (cities and autonomous regions) in spatially related networks, making full use of driving factors strengthening the connection between the agricultural product market and organizations, and enhancing the information and transportation network support.

Characteristics, influence factors, and prediction of agricultural carbon emissions in Shandong Province

LIU Yang, LIU Hongbin

2022, 30(4): 558-569. doi: 10.12357/cjea.20210582

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The Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report indicated that human-induced climate change has already affected many weather and climate extremes in every region across the globe. Greenhouse gases (GHG) produced via the process of agricultural production constitute a large proportion of the total GHG emissions from worldwide production activities. Therefore, estimation of agricultural GHG emissions, analysis of the influencing factors, and prediction of the peak are important. Based on the classical IPCC carbon emission calculation theory, agricultural carbon emissions were estimated for Shandong Province from 2000 to 2020 by using agricultural material input, livestock and poultry breeding, and agricultural soil utilization. The influence factor decomposition was conducted based on Logarithmic Mean Divisia Index (LMDI), and the agricultural carbon emissions from 2021 to 2045 were predicted by using the grey model GM (1, 1). Results showed that the total agricultural carbon emissions in Shandong Province in 2020 were 1.58×10⁷ t and the intensity of carbon emissions was 0.205 t·(10⁴ ¥)⁻¹. Carbon emissions tended to increase from 2000 to 2006 and then decrease from 2007 to 2020; however, the intensity of carbon emissions decreased at an annual rate of 3.8%. The source structure of agricultural carbon emissions was ranked, with agricultural material input, livestock and poultry breeding, and crop farming accounting for 49.6%, 38.5%, and 11.9%, respectively. Carbon emissions and intensities showed regional differences between the 16 cities and tended to increase. Carbon emissions and the intensity of carbon emissions in Heze were higher than those of other cities. The LMDI decomposition results showed that agricultural production efficiency, agricultural industrial structure, regional industrial structure, and rural population were emission reduction factors, whereas regional economic development level and urbanization were emission growth factors. The prediction results showed that agricultural carbon emission of Shandong Province would reach its peak before 2030, and carbon emissions of cities, such as Jinan, Qingdao, Zibo, Weifang, Jining, Tai’an, Weihai, Rizhao, and Liaocheng, would also reach their peaks before 2030. However, the prediction result showed that the agricultural carbon emissions in Zaozhuang, Dongying, Yantai, Linyi, Dezhou, Binzhou, and Heze did not reach their peaks before 2030. Therefore, suggestions for agricultural carbon emission reduction in Shandong Province were put forward.

Spatiotemporal evolution and influencing factors of agricultural carbon emissions in Hebei Province at the county scale

ZHOU Yifan, LI Bin, ZHANG Runqing

2022, 30(4): 570-581. doi: 10.12357/cjea.20210624

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Global climate change, caused by greenhouse gas emissions, is a common challenge for human society. Counties are the smallest administrative units covered by statistics in China, and are also the basic unit at which agricultural carbon emissions data are collected. Studying the spatiotemporal evolution and drivers of agricultural carbon emissions in counties is important for improving the inventory of agricultural carbon emission data, establishing agricultural carbon emission monitoring systems, and formulating regional emission reduction policies. A county-level greenhouse gas emission inventory was established by combining the agricultural greenhouse gas inventory with the characteristics of county data in this study. The agricultural carbon emissions of 168 counties in Hebei Province from 2009 to 2019 were measured firstly, and the spatial and temporal evolution and drivers of agricultural carbon emissions in counties were analyze then from the perspective of spatial spillover using exploratory spatial statistics and spatial measurement methods. The boundary effects of spatial spillover were investigated finally by using a dynamic spatial model to reveal the regular changes induced by the spatial spillover of agricultural carbon emissions in counties with increasing distance. The study results showed that agricultural carbon emissions in Hebei Province were decreasing during the study duration, with land management, livestock and poultry enteric fermentation, and manure management accounting for 33.00%, 42.57%, and 24.33% of agricultural carbon emissions, respectively. A high spatial agglomeration of agricultural carbon emissions at the county scale was found, and the distribution of agricultural carbon emissions hotspots was closely related to the structure of the agricultural industry. The hotspots of agricultural carbon emissions caused by land management were in Shenzhou, Wuqiang, and Raoyang counties in the south of Hebei, whereas the hotspots of livestock emissions were in Fengning, Weichang, Luanping, and Longhua counties in the north of Hebei. County agricultural carbon emissions had a significant spatial spillover effect, and agricultural carbon emissions in neighboring areas increased the overall carbon emissions in the region. Agricultural economic development was the main driver for the increase in agricultural carbon emissions. The agricultural industry structure, mechanization, fertilizer application intensity, rural energy consumption, and farmers’ income were important factors that increased the agricultural carbon emissions. The urbanization rate had an inverse effect on agricultural carbon emissions. Agricultural carbon emissions were affected by both spatial and boundary factors. The spatial spillover of agricultural carbon emissions in the county showed an increasing trend within 30 km, and a decreasing trend within 30–85 km, and the spatial spillover boundary of agricultural carbon emissions was thus approximately 30 km. The spatial spillover of carbon emissions occurred in approximately 6–8 neighboring counties. This study provides a basis and data foundation for establishing regional agricultural carbon emission reduction policies.

Spatiotemporal characteristics and reduction approaches of methane emissions from rice fields in China

TANG Zhiwei, ZHANG Jun, DENG Aixing, ZHANG Weijian

2022, 30(4): 582-591. doi: 10.12357/cjea.20210887

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Rice is the main staple crop in China and methane (CH₄) is the second most important greenhouse gas worldwide. Therefore, it is important to reduce CH₄ emissions from paddy fields. Based on national statistical data and literature collection, we calculated and analyzed the spatial and temporal characteristics of CH₄ emissions at the rice sown-area scale and yield scale in China from 2001 to 2018 and further summarized the key processes and main influencing factors of CH₄ emissions. The results of this study showed that the total sown area of rice and area-scaled CH₄ emissions from rice fields in China showed an overall trend of first decreasing, then increasing, then decreasing again from 2001 to 2018; however, yield-scaled CH₄ emissions in all regions showed a decreasing trend. CH₄ emissions from rice fields mainly included three processes of production, oxidation, and transport, which were mainly influenced by rice varieties, soil characteristics, climatic conditions, and agronomic measures. Owing to the influence of rice sown areas, area-scaled CH₄ emissions from paddy fields in China were high in the southeast and low in the northwest, and yield-scaled CH₄ emissions were high in the south and low in the north. Based on the above findings, this study suggested reducing CH₄ emissions by applying a new rice cultivar, cropping mode, and products with high yield and low CH₄ emissions. Given the regional characteristics of CH₄ emissions in China, this study first proposed the selection of rice cultivars with high yield and low CH₄ emissions and the application of aerobic dry tillage and water-control irrigation in the southern plain region, biochar and lime in the southern hilly region, and aerobic dry tillage and partially alternative urea with ammonium sulfate in the northern rice cropping region. Finally, some suggestions were put forward related to science, technology and policy innovations for CH₄ emission reduction to provide important references for achieving the win-win target of high yield and low CH₄ emissions.

Key biogeochemical processes of carbon sequestration in paddy soil and its countermeasures for carbon neutrality

ZHU Zhenke, XIAO Mouliang, WEI Liang, WANG Shuang, DING Jina, CHEN Jianping, GE Tida

2022, 30(4): 592-602. doi: 10.12357/cjea.20210748

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Rice field ecosystems have dual functions as C sources and C sinks. Soil C sequestration plays an important role in improving the productivity of rice fields, and greenhouse gas emissions from rice fields exacerbate the risk of global warming. Therefore, regulating the C sequestration and emission reduction of paddy soil is of great significance for ensuring food security in China and achieving the goal of “carbon neutrality”. In recent years, researches have focused on the processes and mechanisms of soil organic C (SOC) turnover in paddy fields worldwide. This review summarized the processes and mechanisms of soil C sequestration in paddy fields from the perspectives of sources, transformation, stabilization, and regulation techniques of SOC, and proposed strategies to deal with “carbon neutrality”. SOC is mainly derived from plants and microorganisms. The input of rice rhizosphere C accounted for approximately 28% of the entire underground C input during a single season, and the contribution rates of rice rhizosphere C and microbial assimilated C to the accumulation of SOC were 71.9% and 55.5%, respectively, which were much higher than that of rice straw (12.1%) and the root system (19.8%). After the input of exogenous organic materials into the soil, the decomposition and mineralization of organic materials were first controlled by the dissolution process of SOC, which was the rate-limiting step. The microbial mineralization of the dissolved SOC was affected by the soil moisture conditions, nutrients contents, stoichiometric ratio, microbial activity, and other factors. Apart from the emitted SOC, the remaining inputs were mainly anabolized to form living microorganisms and microbial residues, which were finally fixed in the soil protected by aggregates, organo-mineral colloidal complexes, and necromass (amino sugars). Based on the estimation of assimilation and emission of carbon dioxide, the annual net C sequestration of paddy ecosystems was approximately 156.4 Tg C in China, which proved that paddy soil had a significant C sequestration effect. Although straw removal or incineration, positive priming effects, and other factors decreased the amount of C sequestered in paddy soil, research data had shown that the SOC content of subtropical paddy soil had increased by 60% under the implementation of multiple management strategies such as irrigation and fertilizer application and straw returning in the last 40 years. It had a positive effect on achieving “carbon neutrality” by adopting the management of increasing C sequestration and mitigating greenhouse gas emissions. These management strategies included optimizing the combination of irrigation and fertilizer application and straw returning, establishing an ecological compensation mechanism for C emission reduction, and promoting the inclusion of the rice farming system in the “C trading market”. Therefore, it is necessary to clarify the mechanism of C sequestration in paddy fields, improve the accuracy of estimating and forecasting C neutrality, and accelerate the development of C neutralization technology in paddy fields in future research, which will provide scientific and technological support for achieving the “carbon neutrality” strategic goal in advance.

Key influencing factors and technical system of carbon sequestration and emission reduction in rice production in the middle and lower reaches of the Yangtze River

LIU Tianqi, HU Quanyi, TANG Jichao, LI Chengfang, JIANG Yang, LIU Juan, CAO Cougui

2022, 30(4): 603-615. doi: 10.12357/cjea.20210733

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Rice production is one of the main sources of greenhouse gas (GHG) emissions in China. Aiming at the strategic goals of “carbon peak” and “carbon neutrality,” it is of great significance to explore the key affecting factors and construct a technical system of carbon sequestration and emission reduction in rice production. Aimed at the main rice-producing areas in the middle and lower reaches of the Yangtze River, we conducted positioning experiments, including low-carbon management measures such as no-tillage, deep placement of nitrogen fertilizer, intermittent water-saving irrigation, and combined management of straw and nitrogen fertilizer, to analyze the key influencing factors of carbon sequestration and emission reduction in rice production. Based on a long-term monitoring of GHG emissions from rice fields, we used ¹³C nuclear magnetic resonance technology to analyze the molecular structure of organic carbon functional groups and clarified the mechanism of rice management measures for reducing carbon emissions and increasing carbon sinks. We further evaluated the indirect carbon emissions from rice production under different rice management technologies using the carbon footprint, and clarify the conversion ratio of exogenous straw carbon in rice systems using ¹³C-labeled straw carbon tracing technique. The results of this study showed that regulating the ratio of straw and nitrogen fertilizer could promote the conversion of straw carbon into small molecular functional groups, promote the adsorption of exogenous particulate organic carbon from soil aggregates, and increase the content of intra-aggregate particulate organic carbon by 32.3% in the soil carbon pool compared with those of conventional straw management methods. Intermittent water-saving irrigation technology could reduce methane emissions by 19.9%–21.1% in paddy fields by increasing the abundance of methane-oxidizing bacteria. Low-energy rice field management technologies, such as no-tillage, could reduce fuel and manpower inputs and comprehensively reduce indirect carbon emissions from rice production by 10.5%–16.7%. Compared with the conventional rice straw return mode, management techniques such as intermittent water-saving irrigation and combined straw and nitrogen fertilizer application could increase the exogenous carbon cycle sequestration rate of straw by 57.3%–59.9%. The development of soil aggregate structure, carbon emission functional microorganisms, soil nitrogen substrate concentration, rice production carbon footprint, and crop carbon sequestration are key factors that affect the carbon neutrality of rice production. Establishing a technical system of carbon sequestration and emission reduction from the perspectives of “sinks increase” “emission reduction” “consumption reduction” and “recycling” could promote rice production carbon neutrality by 28.9%–67.6%.

Characteristics of carbon sequestration and methane emission in rice-fish system

DAI Ranxin, ZHAO Lufeng, TANG Jianjun, ZHANG Taojie, GUO Liang, LUO Qiyue, HU Zhongyuan, HU Liangliang, CHEN Xin

2022, 30(4): 616-629. doi: 10.12357/cjea.20210811

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Rice-fish systems are unique rice farming systems that coculture rice with fish (in this paper, “fish” refers to a wide range of aquatic animals including carp, crayfish, shrimp, crabs, and softshell turtles, and others). Studies have shown that the interactions between rice and fish profoundly change the cycling of C, N, and other elements in paddy ecosystems. Whether and how rice-fish coculture affects C sequestration and methane (CH₄) emissions are matters of concern. Based on recently published data, we presented a review of the properties of soil organic C (SOC) and CH₄ emissions in rice-fish systems. Compared with that of the rice monoculture system, the SOC content (0–20 cm soil layer) in the rice-fish system tended to increase. An extra C input due to the feeding and excreta transformation of aquatic animals contributed to the increased SOC in the rice-fish system. CH₄ emissions from the rice-fish system differed greatly among different studies. Some studies have shown that CH₄ emissions from rice-fish systems (e.g., rice-frog, rice-crayfish, and rice-carp) are significantly lower than those of rice monoculture systems, whereas some studies have found that the CH₄ emissions of rice-fish systems (such as rice-carp) are significantly higher than those of rice monoculture. These differences in CH₄ emissions in the rice-fish system could be caused by the type of fish (e.g., carp, crayfish, shrimp, crabs, and softshell turtles), rice variety, paddy environment, and farming management. To improve our understanding of C sequestration and CH₄ emissions in the rice-fish system, more studies and efforts are required. These efforts include i) quantifying the potential of C sequestration and CH₄ emissions in rice-fish systems by establishing long-term studies, examining the variation in C sequestration and CH₄ emissions among different types of rice-fish systems (e.g., rice-carp, rice-crab, rice-turtle, rice-frog, and rice-crayfish), and outlining the general trends of C sequestration and CH₄ emissions in the rice-fish system; ii) understanding the mechanisms by which aquatic animals affect soil C pools and C cycling in paddy ecosystems and examining whether this changed C cycling would affect CH₄ emissions; and iii) development of a technology package for culturing rice and fish, including breeding or selecting rice varieties that can adapt well to rice-fish systems and can reduce CH₄ emissions, optimizing fertilization rates and fertilization methods for rice, optimizing feeding rates and methods for fish, and optimizing strategies of the straw return rate.

Environmental impact assessment of rice-fish culture with different land management models

CUI Wenchao, JIAO Wenjun, MIN Qingwen

2022, 30(4): 630-640. doi: 10.12357/cjea.20210736

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As the goals of carbon peak and carbon neutrality have been proposed, low-carbon and green development has become an inevitable choice for countries worldwide to solve environmental problems and achieve sustainable development. Because agricultural carbon emissions are a considerable part of global carbon emissions, the green transformation and development of agriculture has been regarded as an important basis for the establishment of a green and sustainable economy. Therefore, the study of agricultural carbon emissions is of great significance for China to explore agricultural green transformation and development, and the environmental impact assessment of carbon emissions can provide an important reference for this exploration. This study used the Qingtian Rice-Fish Culture System, the first Globally Important Agricultural Heritage System in China, as the research object, and selected Longxian Village, located in the core area of the heritage site, and Xinpeng Village and Xiaozhoushan Village, located in the radiation area, as the study area. A carbon footprint model based on life cycle assessment was constructed and used to evaluate the environmental impact of rice-fish culture using different land management models. The results showed that 1) although the carbon footprint of the rice-fish culture model that focused on developing terrace tourism was only 5779.1 kg(CO₂-eq)∙hm⁻², thereby making it the most advantageous for carbon emission reduction, its maximum carbon footprint per unit output value was 0.17 kg(CO₂-eq)∙¥⁻¹, which meant that the low economic benefit was not conducive to long-term sustainable development. 2) The economic benefit of the rice-fish culture model that focused on enlarging field fish raising was remarkable, and the carbon footprint per unit output value was only 0.05 kg(CO₂-eq)∙¥⁻¹; however, the high input of agricultural materials made its carbon footprint as high as 7928.6 kg(CO₂-eq)∙hm⁻² and caused high environmental risks. Therefore, a balance between economic output and environmental risk is urgently needed. 3) Supported by the local government, the rice-fish culture model that focused on maintaining traditional farming conserved the heritage of rice-fish culture and had a carbon footprint of 6266.7 kg(CO₂-eq)∙hm⁻² and a carbon footprint per unit output value of 0.12 kg(CO₂-eq)∙¥⁻¹; however, in the long-term, it is also necessary to improve the economic value of products and promote the integrated development of agriculture and tourism to achieve a win-win of economic and ecological benefits. The results reveal the significant differences in the economic and environmental benefits of the rice-fish culture with different land management models and provide a scientific basis for the formulation of green and sustainable development strategies for rice-fish culture systems under different land management models.

Carbon sequestration and greenhouse gas mitigation paths and modes in a typical agroecosystem in northern China

CAI Yurong, WANG Ligang

2022, 30(4): 641-650. doi: 10.12357/cjea.20210789

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Abstract:
“Carbon peak and carbon neutrality” is a commitment of the country to achieve sustainable development in “response and mitigate climate change”, and agroecosystems should bear the corresponding share of non-CO₂ greenhouse gas emission mitigation and farmland soil carbon sequestration. Northern agroecosystems play a pivotal role in ensuring food and ecological security in China, and many previous studies have shown that northern agroecosystems have great potential in N₂O emission mitigation and soil carbon sequestration. However, to ensure food security during the implementation of “carbon peak and carbon neutrality”, how do we choose the path of soil carbon sequestration and non-CO₂ emission mitigation in farmland soil? What are the carbon sequestration and emission mitigation modes of typical agroecosystems in different regions? What problems should be addressed in the implementation of carbon sequestration and emission mitigation? Other issues remain inconclusive or lack systematic research. Therefore, according to the method of agricultural division, the north of China is divided into three agricultural regions, i. e. Northeast China, North China and Northwest China. Based on the systematic analysis of the characteristics of agricultural production in different regions of northern China, this study proposed that the greenhouse gas emission reduction of the northern agroecosystems follows the path of “optimizing production capacity and mitigating emissions (stabilization of productivity of farming and breeding; and mitigation of N₂O emission from farmland, carbon emission from agricultural energy consumption and breeding and its’ wastes)”, and carbon sequestration follows the path of “slow-down and double increase (slow down of the decrease of soil organic carbon of black soil in the Northeast China and increase soil carbon storage of medium and low-yield field and grazing grassland)”. The study puts forward the key contents of carbon sequestration and emission mitigation in different regions. This paper summarizes the technical composition, carbon sequestration and emission mitigation effects, and adaptation area of four modes, namely low carbon cycle mode, capacity expansion and carbon increase mode, carbon optimized breeding mode, and nitrogen saving and carbon conservation mode. Furthermore, this study illustrates that the process of “carbon peak and carbon neutrality” assisted by agricultural production in northern China needs to focus on “coordination of carbon sequestration and emission mitigation, efficiency of carbon sequestration and emission mitigation, large-scale implementation of technology and mode” to provide ideas and support for the development of “low-carbon” green agroecosystems in northern China.

Carbon neutralization potential and carbon sequestration efforts in a wheat-maize rotation system in the North China Plain

WANG Yuying, HU Chunsheng, DONG Wenxu, ZHANG Yuming, LI Xiaoxin, LIU Xiuping

2022, 30(4): 651-657. doi: 10.12357/cjea.20210747

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Abstract:
Agricultural C neutralization is an effective method of using industrial carbon dioxide (CO₂) in agricultural production. Aiming at the national goal of “peaking CO₂ emissions before 2030 and achieving carbon neutrality before 2060”, we defined the agricultural non-energy C balance in the North China Plain (NCP) by using the “static chamber-eddy covariance-biomass monitoring method”. Simultaneously, C emissions from agricultural energy were determined based on the sampling survey data of farmers and the C emission coefficients of agricultural activities. Thus, the C neutralization potential of croplands in this region was calculated. Our results showed that in the NCP, the net amount of organic C (including grains and returned straw) for winter wheat and summer maize was 604 g(C)∙m⁻² and 540 g(C)∙m⁻², respectively. Considering the ecosystem autotrophic respiration consumption, the net C sequestration of non-energy C was −359 g(C)∙m⁻² and −143 g(C)∙m⁻² in the wheat and maize seasons, respectively. Energy C emissions in the system were further studied. The C emissions of pesticides, chemical fertilizers, agricultural diesel, and irrigation in the wheat season were 3.74, 90.70, 5.68, and 2.05 g(C)∙m⁻², respectively; and those in the maize season were 2.89, 53.70, 10.20, and 2.05 g(C)∙m⁻², respectively. Combined with the non-energy and energy C budget, both the winter wheat and summer maize seasons were C sinks, −257 g(C)∙m⁻² for the winter wheat season and −74 g(C)∙m⁻² for the summer-maize season. For example, in Luancheng (located in Hebei Province), a typical intensive and high-yield grain region in the NCP, the annual C sequestration potential of winter wheat and summer maize croplands was 3.8×10¹⁰ g C and 9.4×10⁹ g C, respectively. In addition, strengthening cultivated land management, promoting low-C agriculture, and developing C-rich agriculture can be effective strategies for C sequestration in this region. In conclusion, we identified the C sink intensity of winter wheat and summer maize rotation cropland in the NCP, estimated the C neutralization potential in Luancheng, Hebei Province, and proposed effective C sequestration efforts.

Conservation agriculture-mediated soil carbon sequestration: A review

XU Yingde

2022, 30(4): 658-670. doi: 10.12357/cjea.20210889

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Abstract:
Soil organic carbon (SOC) sequestration is an important driving force for mitigating global climate change and maintaining farmland productivity. Clarifying the accumulation and stabilization mechanism of SOC and its influencing factors can help regulate the soil carbon (C) sink potential scientifically. In addition, under the challenge of global ecological environment degradation and food security pressure, seeking sustainable farmland management has become an urgent task. Conservation agriculture (CA) has an important impact on SOC sequestration and helps to achieve a win-win situation between food production and ecological benefits. However, given the complexity of soil systems, a systematic theory of soil C pool formation under the control of CA has not yet been formed. In this context, a review is presented with the introduction to and discussion on different sequestration pathways of SOC and its stabilization mechanism, the connotation and main components of CA, and the effect of conservation CA on SOC sequestration. Besides, the mechanism of SOC sequestration under the regulation of CA is discussed in detail. On the basis of existing study, modern organic C separation and biomarker technologies should be used to clarify the microbial-aggregate-mineral synergistic mechanism of SOC sequestration mediated by CA, and pay attention to the deep soil C sequestration process. In addition, the establishment of a long-term study system for CA will contribute to improving the regulation of CA on the potential and essence of SOC. finally, a SOC management framework based on farmland practice should be built to help land managers and farmers to formulate scientific and reasonable sustainable land use strategy.

Effects of tillage rotation modes on soil carbon sequestration and carbon pool management index of farmland in northern Henan

ZHU Changwei, CHEN Chen, NIU Runzhi, LI Yang, JIANG Guiying, YANG Jin, SHEN Fengmin, LIU Fang, LIU Shiliang

2022, 30(4): 671-682. doi: 10.12357/cjea.20210741

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Abstract:
To explore the effects of different tillage rotation modes on soil carbon sequestration and carbon pool management index of farmland in northern Henan, a field experiment comprising five treatments with different tillage modes was carried out during wheat seasons from 2016 to 2020 in fluvo-aquic soil in northern Henan. The treatments were: 1) continuous rotary tillage (RT-RT-RT, CK); 2) deep tillage-rotary tillage-rotary tillage (DT-RT-RT); 3) deep tillage-rotary tillage-shallow rotary tillage (DT-RT-SRT); 4) deep tillage-shallow rotary tillage-shallow rotary tillage (DT-SRT-SRT); 5) deep tillage-shallow rotary tillage-rotary tillage (DT-SRT-RT). Soil bulk density, soil organic carbon (SOC), liable organic carbon (LOC), non-liable organic carbon (NLOC), organic carbon storage, and carbon pool management index (CPMI) in 0–50 cm soil layers were measured and analyzed. The results showed that the soil bulk density in the 0–40 cm soil layer decreased under rotation tillage treatments. In the 0−20 cm soil layer, the SOC, LOC, and NLOC contents, with values of 11.54 g∙kg⁻¹, 3.31 g∙kg⁻¹, 8.30 g∙kg⁻¹, respectively, were the highest under DT-SRT-SRT and were significantly higher than those under RT-RT-RT. Compared with those under RT-RT-RT, the SOC, LOC and NLOC contents in the 10−40 cm soil layer were significantly higher under DT-SRT-RT. The rotation tillage treatments reduced LOC/SOC but increased NLOC/SOC, especially in the 20−40 cm soil layer; the highest increment was 7.5%. During the experimental period, each rotation tillage treatment increased the soil organic carbon storage in the 0−40 cm soil layer. In 2019, the organic carbon storage in the 0−30 cm layer was highest under DT-SRT-SRT (36.64 Mg·hm⁻²). However, the organic carbon storage in the 0−40 cm soil layer, which increased by 12.8% and 9.7%, respectively, during 2019 and 2020 compared with that under RT-RT-RT, and was highest under DT-SRT-RT. In 2019, the activity index of carbon pool in the 0−40 cm soil layer under DT-SRT-RT was reduced. The CPMI was relatively low, with a maximum reduction of 4.3%. In 2020, DT-SRT-RT significantly increased the carbon pool index and CPMI values in the 0−40 cm soil layer; the highest CPMI was 108.5. Generally, deep tillage-strip rotary tillage-rotary tillage reduced soil bulk density; increased contents of SOC, LOC, and NLOC as well as NLOC/SOC value; and increased the organic carbon storage in 0−40 cm soil layer; therefore, it was suggested as the optimum practice for carbon sequestration of farmland in northern Henan.

Effects of rotation tillage on available nutrients and structural characteristics of dissolved organic carbon of Fluvo-aquic soil in northern Henan Province

ZHU Xuanlin, ZHU Changwei, CHEN Chen, LI Yang, NIU Runzhi, JIANG Guiying, YANG Jin, SHEN Fengmin, LIU Fang, LIU Shiliang

2022, 30(4): 683-693. doi: 10.12357/cjea.20210743

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Abstract:
Tillage is an important practice for improving soil quality. The effects of tillage on soil nutrient contents are well known. However, the understanding of the effects of tillage on soil dissolved organic carbon (DOC) and its structure is rare. This study aimed to select optimum tillage mode by exploring the effect of tillage mode on DOC and its structure in Fluvo-aquic soil in northern Henan Province. A field experiment was carried out using five treatments designed with different tillage rotation modes during the wheat season. The treatments were as follows: 1) continuous rotary tillage (RT-RT-RT); 2) deep tillage-rotary tillage-rotary tillage (DT-RT-RT); 3) deep tillage-rotary tillage-strip rotary tillage (DT-RT-SRT); 4) deep tillage-strip rotary tillage-strip rotary tillage (DT-SRT-SRT); 5) deep tillage-strip rotary tillage-rotary tillage (DT-SRT-RT). The contents of alkaline hydrolysis nitrogen (AN), available phosphorus (AP), available potassium (AK), DOC, degree of humification, molecular weight and polymerization degree of organic matter, proportion of hydrophobic components, degree of aromatization and molecular weight of soil were measured and analyzed. The results showed that the difference in all the indexes among treatments was mainly demonstrated in the 0–40 cm soil layer. Compared with those under RT-RT-RT in the 0–40 cm soil layer, the AN, AP, and AK increased by 17.8%, 17.2%, and 19.6% (P<0.05), respectively, under DT-SRT-RT, whereas the DOC content, degree of humification, and proportion of hydrophobic components increased by 20.2%, 53.1%, and 27.4% (P<0.05), respectively, under DT-SRT-RT. Compared with those under RT-RT-RT, the aromatization degree and molecular weight in the 20–30 cm soil layer increased by 21.0% (P<0.05), and the molecular weight and polymerization degree of organic matter in the 10–30 cm soil layer decreased by 36.7% (P<0.05) under DT-RT-SRT. Available soil nutrients and DOC and its structural characteristics were affected by soil depth, tillage mode, and the interaction between soil depths and tillage modes. The correlation among different indices decreased with increasing soil depth. In summary, compared with continuous rotary tillage, DT-SRT-RT improved soil available nutrients and DOC content and increased the complexity of the DOC structure. Therefore, the DT-SRT-RT mode was suggested as a suitable rotation tillage mode in the Fluvo-aquic soil areas of northern Henan.

Effect of long-term fertilization on the stabilization of soil organic carbon by iron oxides in red soil

WAN Dan, WANG Boren, ZHANG Lu, ZHANG Ting, CHEN Jiubin, YU Guanghui, HAN Yafeng, HUANG Qiaoyun

2022, 30(4): 694-701. doi: 10.12357/cjea.20210705

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Abstract:
The preservation and decomposition of soil organic carbon (SOC) has been the subject of scientific inquiry for decades, owing to its critical role in regulating atmospheric CO₂ concentrations. Iron (Fe) oxides are widely recognized as a rusty sink for carbon (C) because of their large surface area and high adsorption affinity. Fe oxides such as amorphous Fe hydroxides, crystalline Fe hydroxides, and organo-Fe complexes coexist in soils and can be converted to one another. An in-depth understanding of the stabilization of SOC by different types of Fe oxides will strengthen our understanding of soil C cycling. Based on a long-term (25 years) fertilization field experiment in Hengyang, Hunan Province, China, investigations were performed to clarify the stabilization of SOC using different Fe oxides, and its responses to long-term fertilization were discussed. A selective extraction was conducted sequentially to determine the distribution of organic carbon (OC) among different Fe oxides: Na-pyrophosphate (organo-Fe complexes) followed by HCl-hydroxylamine (amorphous Fe hydroxides) and dithionite-HCl (crystalline Fe hydroxides). Ultraviolet and visible light adsorption measurements were used to analyze the composition of Fe oxide-bound OC. The OC contents differed among different Fe oxides in the red soil in the following order: organo-Fe complex-bound OC (2.45–3.59 g∙kg^–1, OC_PP) > crystalline Fe hydroxide-bound OC (1.46–1.51 g∙kg^–1, OC_DH) > amorphous Fe hydroxide-bound OC (0.39–0.70 g∙kg^–1, OC_HH). OC_PP was formed by the coprecipitation/chelation of organo-Fe complexes with low aromaticity, high molecular weight, and high hydrophobicity compounds. OC_HH and OC_DHwere primarily formed by Fe hydroxide-adsorbed aromatic compounds. OC_HHhad greater average molecular weights and higher aromaticity than OC_DH. Long-term application of chemical fertilizers (NPK) facilitated (P<0.05) the binding of OC with organo-Fe complexes and amorphous Fe hydroxides. However, organic fertilizer (M) addition solely increased (P<0.05) the association of OC with amorphous Fe hydroxides. In addition, NPK treatments increased (P<0.05) the average molecular weights of OC_DH and the hydrophobicity and aromaticity of OC_PP. However, M treatments decreased (P<0.05) the average molecular weights of OC_PP and the hydrophobicity and aromaticity of OC_PP and OC_HH. These findings suggest that long-term fertilization may increase the stabilization of SOC by Fe oxides in red soil; however, the response of SOC stabilization by Fe oxides with varying crystallinity to long-term fertilization is different. In addition, long-term fertilizer addition may change the composition of Fe oxide-bound OC.

Greenhouse gas emission reduction effect of a straw briquette central heating system

FENG Xinxin, ZUO Tao, SUN Ning, XIE Jie, GAO Chunyu, BI Yuyun, WANG Yajing

2022, 30(4): 702-712. doi: 10.12357/cjea.20210679

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Abstract:
The long-term dependence on coal for heating during winter in northern China has caused serious environmental pollution. In addition, the limitations and non-renewability of fossil fuels have prompted the development of new energy sources for clean heating. Biomass energy resources are a good option because they are abundant, clean, and sustainable. Crop straw is an important agricultural biomass energy resource in China because of its’ high yield, wide distribution, and variety. Extruding straw into briquette fuel can significantly improve its combustion performance. Referring to the Intergovernmental Panel on Climate Change (IPCC), the United Nations Framework Convention on Climate Change (UNFCCC), and the Clean Development Mechanism (CDM) methodology, and through literature research and field surveys, this study constructed a calculation method for greenhouse gas emission reduction in a straw briquette fuel central heating system, with the natural decomposition of straw as the baseline. The calculation method involves four parts: the system boundary, baseline emissions, project emissions, and leakage. The system boundary includes the disposal of waste straw in the absence of the system, the route of transporting waste straw to the straw molding processing plant, the briquetting machine used in the molding process, the boiler used in the central heating process, the route to transport the straw briquette to the heating point, and the place where the straw briquette is used for heating. Baseline emissions are the sum of greenhouse gas emissions from the natural decomposition of straw, emissions from alternative coal heating, and energy consumption emissions from chemical fertilizer production replaced by returning ash generated by straw to the field. Total emissions of the system are the sum of fossil fuel consumption emissions from engineering transportation activities, power consumption emissions from straw molding, and emissions from utilizing straw molding fuel combustion and heating. The system leakage rate is zero. Finally, the total calculation formula is as follows: net greenhouse gas emission reduction of straw briquette fuel central heating system = baseline emission − energy consumption emission in straw utilization process − project leakage. Using the above methods, a case study was conducted on a straw briquette central heating project in Lintao County, Gansu Province, China. The results showed that in the heating season from 2019 to 2020, the baseline emission of the Lintao straw briquette central heating project was 1610.08 t CO₂, the project emission was 104.67 t CO₂, and the net emission reduction was 1505.41 t CO₂, which is equivalent to reducing the CO₂ emission of 529.45 t of standard coal. For every 1 t of corn straw raw material consumed by the Lintao straw briquette central heating system, the CO₂ emissions are reduced by 1.17 t. Therefore, it can be concluded that the straw briquette central heating system has an obvious emission reduction effect. This study established a quantitative calculation method for greenhouse gas emission reduction for a straw-briquette-based central heating system based on the background of natural straw decomposition, which enriches the estimation methodology for greenhouse gas emission reduction evaluations. This quantitative study demonstrated that large-scale straw briquette-based central heating projects have a significant emission reduction effect.

2022 Vol. 30, No. 4