中国生态农业学报(中英文)

Review on measurement of agricultural carbon emission in China

HU Yonghao, ZHANG Kunyang, HU Nanyan, WU Laping

2023, 31(2): 163-176. doi: 10.12357/cjea.20220777

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Abstract:
Accurate measurement of carbon emissions is crucial for achieving dual-carbon goals. Agricultural carbon emissions are affected by various crop types, production methods, geographical locations, and other factors. Therefore, although scholars have attempted to measure China’s agricultural carbon emissions from different perspectives, a consistent and effective conclusion regarding the estimation method, sample selection, and calculation results does not exist. First, this study introduces the main accounting methods for agricultural carbon emissions, including the emission factor method, model simulation method, and field measurement method. Second, it segregates agricultural carbon emission accounting methods from the existing four aspects: input and output, production process, carbon sequestration, and carbon footprint. Third, the accounting results for agricultural carbon emissions are summarized. Finally, the limitations of the existing research are analyzed, and a prospect for agricultural carbon emission accounting is specified. This study discovered shortcomings in the existing research, including the omission of emission sources, inappropriate use of emission factors, and excessive concentration perspectives at the macro level. Future research can be continued from the following aspects: constructing a scientific and comprehensive agricultural carbon emission accounting system, improving emission factors, and strengthening micro-level research on farmers.

Research progress of greenhouse gas emissions and sequestration of the Chinese food system

JIN Xinpeng, BAI Zhaohai, MA Lin

2023, 31(2): 177-193. doi: 10.12357/cjea.20220025

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Studies on the country’s food system and greenhouse gas (GHG) accounting are still lacking in China. Most of previous studies have focused on crop and livestock production, which are hard to meet the demands of both GHG reduction and sequestration, against the backdrop of the “carbon peak and neutrality” policy. In this study, we proposed a food system GHG accounting framework that covers land use, land use change, and forests (LULUCF); agricultural production; and post-production food supply sectors. Through literatures review, collecting emission data, and reverse-calculating emission factors, we analyzed the differences in accounting methods and the uncertainties of emission parameters for various GHG emission (or sequestration) segments in the Chinese food system. Results showed that the coefficients of variables (CVs) of the emission or storage parameters of manure and crop straw application, pesticides and film production, food processing, food retail and wholesale, and grassland sinks were above 35%. Our suggestions for future studies are as follows: 1) in the agricultural production sector: refine emission factors of agricultural activities, harmonize different energy use accounting methods (e.g., final energy consumption accounting and process-based accounting methods), and reinforce research on energy consumption of agricultural input manufacturing enterprises; 2) in the LULUCF sector: establish the land use classification dedicated to global change research, identify the land use processes associated with the food system, and cross-check the field measure-based accounting method and the process-based accounting method; 3) in the post-production food supply sector: clarify the accounting scopes of each stage and select the environmental input-output life cycle assessment method, the process-based life cycle assessment method, or the final energy consumption accounting method. This study could further provide scientific basis for GHG reduction in food systems.

Using soil organic carbon isotope composition analysis to elucidate the carbon cycle of agroecosystems

LI Fadong, LI Zhaoxin, QIAO Yunfeng, LIU Shanbao, TIAN Chao, ZHU Nong, HIRWA Hubert, MEASHO Simon

2023, 31(2): 194-205. doi: 10.12357/cjea.20230029

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Soil organic carbon is one of the most abundant and longest stored ecosystem carbon pools on the Earth’s surface. Improving soil organic carbon stability and enhancing soil carbon sink capacity have become a key scientific issue for sustainable strategies of carbon management in terrestrial ecosystems. There is an international consensus that agroecosystems are playing an increasingly important role in carbon sequestration and in the process of achieving carbon neutrality. Farmland management practices could disturb soil carbon cycle processes, and the carbon sink of agroecosystems can be enhanced by effective management practices. Currently, domestic studies have focused on the effects of tillage practices, fertilizer and irrigation levels, and straw incorporation on farm productivity, carbon sequestration rate, and greenhouse gas emissions; but the mechanisms of organic carbon stability in response to different farmland management practices and the relationship with soil carbon emissions have not been clearly understood. ¹³C isotope technology is a powerful tool for studying soil carbon cycling processes in agroecosystems. By measuring the isotopic abundance of different organic carbon components in soil carbon emissions, soil respiration components and sources can be accurately distinguished, which can better reveal the response mechanism of soil organic carbon stability to farmland management practices and provide a scientific basis for enhancing soil carbon sink effects and sustainable agricultural development. Most previous studies have focused on simulations and small-scale, short-term monitoring, with large discrepancies between results, which may overestimate or underestimate the actual values. Therefore, multi-point, long-term, and real-time in situ monitoring combined with ¹³C isotope technology should be adopted in future research on the soil carbon cycle to understand real-time decomposition of soil CO₂ emissions in agroecosystems, which can better reveal the mechanism of soil organic carbon stability.

Development measures of the fertilizer industry under the carbon peaking and carbon neutrality goals: Analysis of carbon emission reduction and existing problems from 2011 to 2020

LI Hua, LI Xiuying, WANG Lei, LI Yuyi, WANG Jing

2023, 31(2): 206-213. doi: 10.12357/cjea.20220528

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Carbon peaking and carbon neutrality have become common goals in global development. Fertilizers play a dual role in carbon emissions. They not only emit carbon due to energy consumption but also reduce carbon emissions by improving the carbon sequestration capacity of crops. Fertilizers will continue to play an irreplaceable role in food and agricultural production for the near future. Appropriate fertilizer products and scientific applications can support carbon emission reduction. This study used data published by the FAO, the National Bureau of Statistics, the Ministry of Agriculture and Rural Affairs of China, and other websites to analyze the current situation of carbon emission reduction in China’s fertilizer industry. It identified the existing problems and discussed the development measures of the fertilizer industry under the carbon peaking and carbon neutrality goals, in the hope of providing a reference for the low-carbon development of the fertilizer industry. The results showed that China’s fertilizer industry had made remarkable progress in reducing carbon emissions from 2011 to 2020. Following an increase, the production and application of chemical fertilizers decreased, which made the largest contribution to emissions reduction from agriculture. The output of N, P₂O₅, and K₂O in China decreased from the highest level of 7.43×10⁷t in 2015 to 5.50×10⁷t in 2020, a decline of 26.05%. The amount of chemical fertilizer application decreased by 12.82% from the highest 6.02×10⁷t in 2015 to 5.25×10⁷t in 2020. The carbon emissions from chemical fertilizers in China decreased from 3.35×10⁸ t CO₂ eq in 2015 to 2.74×10⁸ t CO₂ eq in 2020, dropping 18.21%. The output of organic fertilizers was on the rise, which was conducive to carbon sequestration and emission reduction. In 2020, the output of organic fertilizers reached 1.56×10⁷ t, up by 29.46% over the 2015 level. Owing to the rapid extension of scientific fertilization technologies, the utilization rate of chemical fertilizers for three major grain crops, namely rice, corn, and wheat, had increased yearly to 40.20% in 2020, up by 5 percentage points over 2015. However, the fertilizer industry in China faced problems, including higher application amounts, low absorption, insufficient innovation, market disorder, unscientific fertilization, inadequate organic fertilizers, and weak legislation and supervision. To achieve carbon peaking and carbon neutrality goals, China’s fertilizer industry should strive toward the following five aspects: developing new types of fertilizers, promoting science-based technologies for energy-efficient use of fertilizers, improving comprehensive utilization of agricultural wastes, strengthening legislation and supervision of the fertilizer industry, and enhancing publicity and training in scientific low-carbon fertilization.

Research on green agricultural development under the dual-carbon goal: review and perspectives

ZHANG Kangjie, YU Fawen

2023, 31(2): 214-225. doi: 10.12357/cjea.20220888

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The dual-carbon (Carbon Peaking and Carbon Neutrality) goal initiates new requirements for agricultural green development, especially the green transformation of agricultural production methods, which is particularly urgent. Based on the analysis of the connotation and principles of agricultural green development, this study explored the current situation and future development focus of agricultural green development using the literature induction method. Furthermore, the research progress of agricultural green development was systematically sorted into four system levels, namely: production, industry, operation, and policy. Finally, the research status of agricultural green development under the dual-carbon goal was reviewed, and its future research trend was investigated. The study showed that the research on agricultural green development mainly focuses on basic theories, indicator measurements, development statuses, production systems, and supporting policies. However, research on the connotation and extension, as well as the system innovation of agricultural green development under the dual-carbon goal, is relatively weak. In the future, research on agricultural green development under the dual-carbon goal should focus on scientifically defining the new connotation of agricultural green development, comprehensively expounding the relationship between dual-carbon goals and agricultural green development, and constructing an evaluation index system for agricultural green development with localized Chinese characteristics. On this basis, the dilemma of agricultural green development should be diagnosed from the perspective of the entire agricultural industry chain, and future development focus should be determined against the dual-carbon target. In particular, we should explore the direction of multi-dimensional innovation; deeply integrate digital empowerment, subject cultivation, market guidance, organization guidance, and other innovative elements; and accelerate the innovation of the agricultural green development system under the dual-carbon goal from the four abovementioned aspects to provide a scientific basis and theoretical support for agricultural green development and comprehensively promote the rural revitalization strategy.

Effects of agricultural technical efficiency on agricultural carbon emission: Based on spatial spillover effect and threshold effect analysis

YAN Guangyao, CHEN Weihong, QIAN Haihui

2023, 31(2): 226-240. doi: 10.12357/cjea.20220571

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Global warming, caused by the greenhouse effect, has triggered numerous unprecedented extreme weather events globally. Agricultural technology is the fundamental force that promotes the development of the agricultural industry. Studying the impact mechanism of agricultural technology on agricultural carbon emissions will help transform traditional agriculture into ecological, green, and low-carbon modern agriculture, and it is of great significance to the realization of carbon neutrality and carbon peaks. This study used panel data from 31 provinces and cities in China from 2001 to 2020. First, the stochastic frontier model was used to extend existing research from a broad and narrow sense of agricultural technical progress to agricultural technical efficiency. The total agricultural carbon emissions and intensity of agricultural carbon emissions were then calculated and compared. Finally, we constructed the spatial Dubin model and the threshold model with agricultural technical efficiency as the threshold variable, which revealed the spatial effect and non-linear relationship between agricultural technical efficiency and agricultural carbon emissions. The results showed that the total and intensity of agricultural carbon emissions had decreased in recent years. Central China had more agricultural carbon emissions than eastern and western China, and eastern China had a higher technical efficiency of agriculture and a lower carbon emission intensity of agriculture than central and western China. Agricultural carbon emission intensity and technical efficiency had spatial autocorrelation and agglomeration characteristics, and high-high clustering and low-low clustering are the main factors among the provinces. Agricultural carbon emission intensity had a positive spatial spillover effect on itself, but agricultural technical efficiency had a negative spatial spillover effect, which was conducive to the overall reduction of agricultural carbon emissions. Additionally, urbanization, human capital level, and per capita cultivated land area also had negative effects on agricultural carbon emission intensity, but the level of agricultural economic development and the degree of agricultural disaster had positive effects. There was a double threshold effect between agricultural technical efficiency and agricultural carbon emission intensity, which meant that when agricultural technical efficiency reached the “inflection point”, its impact on agricultural carbon emission intensity became negative, and after the level of agricultural technical efficiency was further improved, its influence weakened due to the diminishing marginal effect. Most existing research began with a broad or narrow definition of technological progress, but this study used technical efficiency as the research object after the decomposing technological progress in a broad sense, which further validated the indisputable and decisive role of technological progress in agricultural energy conservation and emission reduction. This study provides a theoretical and policy basis for exploring the path to achieving the “double carbon” goal.

Impact of structural transformation, technological progress choice on agricultural carbon shadow price: An empirical analysis based on BP technology and a mediating effect model

XU Biaowen, WANG Haiping, SHEN Zhiyang

2023, 31(2): 241-252. doi: 10.12357/cjea.20220492

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The effective implementation of emission reduction strategies through economic structural transformation and technological progress has become an inevitable choice for achieving low-carbon economic and social transformation and development in China. Considering that the disposability assumption of the shadow price calculation method is inconsistent with the realistic theory in the existing literature, a new calculation method for the carbon shadow price based on the data envelopment analysis (DEA) framework modeling and satisfying the principles of economic theory and material conservation was applied, in which the expected output production sub-technology and the undesired output production sub-technology are linked according to the generation relationship of pollutants. Improved By-production technology was used to accurately measure the agricultural carbon shadow price in 31 provinces from 1997 to 2020, and kernel density was used to analyze the dynamic evolution characteristics of agricultural carbon shadow prices. A feasible generalized least squares (FGLS) model was used to examine the impact of structural transformation and technological progress choices on the shadow price of agricultural carbon emissions. The results showed that: 1) the shadow price of agricultural carbon price showed an increasing trend, which was 7759.69 ¥∙t⁻¹ in the east region, 4192.35 ¥∙t⁻¹ in the central region, and 3997.51 ¥∙t⁻¹ in the west region, and the rising rates decreased in that order. 2) Kernel density analysis revealed that the kernel density value of the agricultural carbon shadow price had an increasing trend. The kernel density curve in the east region was right-shifted, in the central region left-right shifted with increasing regional differences, and in the west region it was downward and widened. 3) The overall regression analysis showed that the shadow price of agricultural carbon was significantly increased by structural transformation and labor-saving technological progress but that this increase was inhibited by capital deepening. Meanwhile, the level of economic development, the scale of agricultural operations, urbanization, and the level of opening up all played important roles in the agricultural carbon shadow price. 4) The regional regression analysis results highlighted that the influencing factors of agricultural carbon shadow prices differed in different regions. Structural transformation significantly increased the carbon shadow price in the east region but significantly inhibited it in the west region. Labor-saving technological progress reduced the carbon shadow price in the east region while significantly increasing it in the west region. Therefore, it is necessary to promote the transformation of the industrial structure, formulate differentiated green and coordinated development policies, and establish an agricultural carbon emissions trading market to promote low-carbon, green, and high-quality agricultural development.

Carbon budget and driving factors in marine fisheries in Liaoning Province, China

LI Yuan, LI Tianhui, LIANG Jinshui, LI Faxiang, LIU Changfa

2023, 31(2): 253-264. doi: 10.12357/cjea.20220542

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Marine fisheries are valuable oceanic carbon sinks that store and sequester carbon. They act as both “carbon sources” and “carbon sinks”, and this is particularly important to achieve the established carbon peak and carbon neutrality goals. The amount of carbon sequestered by fisheries and its economic value in Liaoning Province from 2006 to 2020 were calculated based on the China Fisheries Statistical Yearbook, the Calculation Reference of Oil Consumption for Oil Price Subsidy of Domestic Fishing Vessels, and the China Statistical Yearbook. Then, a cubic exponential smoothing method was applied to a time-series forecasting model to predict the same parameters for 2021–2030, and the factors controlling the amount and economic value of carbon sequestered in fisheries in Liaoning Province were examined using gray correlation analysis. The results showed that 1) the surplus of income and expenditure for carbon sequestration in marine fisheries in the region decreased each year from 2006 to 2020, and the deficit is predicted to intensify in 2021–2030. 2) The maximum surplus of carbon (sequestration minus emissions) was 256.36×10⁴ tons and the maximum deficit was 29.99×10⁴ tons, with an average of 116.66×10⁴ tons per year. 3) The total amount of carbon sequestered by shellfish and algae was 241.67×10⁴tons, 83% of which was attributed to the aquaculture industry, with little change. 4) The average amount of carbon emissions form marine fishing was 164.52×10⁴ tons per year, almost 50% of which was attributed to trawling. The amount of carbon sequestered from marine fishing could not compensate for carbon emissions after 2017. 5) The total economic value of sequestered carbon of marine fisheries of Liaoning Province was 27.423 billion Yuan, with an annual average of 1.828 billion Yuan. 6) The total amount and economic value of carbon sequestered in marine fisheries continued to decline and were positively correlated. 7) The amount of sequestered carbon was also positively correlated with fishing yields, shellfish production, and macroalgal culture. The amount and economic value of carbon sequestered in marine fisheries in Liaoning Province were significantly influenced by national policies, fishing yield, number of employees, area of shellfish and macroalgal aquaculture sites, and the total power of fishing vessels (which determined the vessels’ carbon emissions). To protect marine biodiversity and promote the sustainable development of marine fisheries in the area, it is recommended to integrate multiple aquaculture systems, reduce high-energy-consuming fishing operations, and strengthen the monitoring of highly polluting fishing vessels.

Evaluation of agricultural carbon emissions in Xinjiang and analysis of driving factors based on machine learning algorithms

DENG Lu, YUAN Shengbo, BAI Ping, LI Huifang

2023, 31(2): 265-279. doi: 10.12357/cjea.20220501

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Abstract:
Agriculturl carbon emissions are the second-largest source of carbon in the world. Therefore, clarifying the patterns of agricultural carbon emissions is crucial for achieving carbon peaks and neutrality. To explore the law of agricultural carbon emissions in Xinjiang and promote agricultural carbon emission reduction, agricultural carbon emissions in Xinjiang were measured based on carbon emission coefficients published according to the carbon emission links generated in the process of agricultural production. Furthermore, spatial correlation models, such as the Moran and learned index structure for spatial data (LISA) indices, were used to measure the spatial clustering patterns of agricultural carbon emissions in Xinjiang. A random forest machine learning model was then used to quantitatively analyze the factors influencing the efficiency of agricultural carbon emissions. The results indicated that: 1) agricultural carbon emissions grew slowly from 2010 to 2019, from 292.24×0⁴ t to 379.69×10⁴ t, with an average annual growth rate of 3.33%. 2) Applications of chemical fertilizers and agricultural films were the main sources of agricultural carbon emissions in Xinjiang, accounting for 58.06% and 39.03%, respectively. 3) Xinjiang’s agricultural carbon emission efficiency increased steadily, with a faster growth from 2010 to 2013 and a slower growth from 2014 to 2019. The main distribution range of carbon emissions efficiency increased from less than 50 ¥∙t⁻¹ to 50–100 ¥∙t⁻¹. 4) The agricultural output values in the high-high agglomeration areas of Xinjiang with high agricultural carbon emission efficiency were relatively low because of the low material input. In contrast, the agricultural output values in the low-low agglomeration areas were relatively high, however, where the level of technology and management was low, and the material input was extremely high. The efficiency of agricultural carbon emissions in Xinjiang has room for improvement. 5) Overall agricultural carbon emission efficiency was higher in the southern region with lower precipitation, whereas the northern region with higher precipitation exhibited moderate emissions. Precipitation may indirectly affect agricultural carbon emission efficiency by affecting the level of agricultural development and production technology. 6) Carbon emission efficiency decreased sharply with increased agricultural scale when the agricultural scale was between 0.12 and 2.02 hm² per person. Moreover, the influence on agricultural carbon emissions efficiency decreased when the agricultural scale exceeded 2.02 hm² per person. There was a significant negative effect on agricultural carbon emission efficiency when cultivated land was between 120 and 17 220 hm². In contrast, its’ effect on agricultural carbon emission efficiency was more moderate when cultivated land was larger than 17 220 hm². Rural economic development level had a positive effect on carbon emission efficiency. Furthermore, carbon emission efficiency exhibited a “U” shaped pattern as a function of agricultural electrification degree. Comprehensively considering the two aspects of improving agricultural output value and agricultural carbon emission efficiency, the degree of agricultural scale and the scale of arable land should be further improved to increase agricultural output value, and the level of rural economic development and the degree of agricultural electrification should be further improved to increase the efficiency of agricultural carbon emissions.

Effects of gypsum application on grain yield and methane emissions in rice paddies: a global meta-analysis

MENG Yi, LIAO Ping, WEI Haiyan, GAO Hui, DAI Qigen, ZHANG Hongcheng

2023, 31(2): 280-289. doi: 10.12357/cjea.20220428

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Gypsum is a widely recommended soil amendment for rice paddies, but a meta-analysis of the responses of rice yield and greenhouse gas emissions to gypsum application has less been reported. In this study, a global meta-analysis was conducted to quantify the effects of gypsum application on rice yield and greenhouse gas emissions. The dataset was collected from 74 studies involving 382 pairs of rice yield observations, 39 pairs of methane emission observations, 10 pairs of nitrous oxide emission observations, 10 pairs of area-scaled global warming potential (GWP) observations, and 10 pairs of yield-scaled global warming potential (GHGI) observations, where the absence of gypsum acted as the control and the application of gypsum acted as the treatment. Based on a meta-analysis, the effects of gypsum application on rice yield and paddy CH₄ emissions were examined under different gypsum application measures (type and application rate), soil properties (pH, organic carbon content, and texture), and field management methods (N rate, irrigation regime, rice type, and experiment type). Overall, gypsum application significantly increased rice yield (+58%) and reduced CH₄ emissions (−47%), GWP (−22%), and GHGI (−31%), but did not affect N₂O emissions relative to those without gypsum application. The magnitude of the increase in rice yield and reduction in CH₄ emissions of desulfurization gypsum was significantly higher than that of gypsum and phosphogypsum. Applying gypsum increased rice yield at gypsum rates ≥ 2 t·hm⁻², while no significant effects were observed at gypsum rates < 2 t·hm⁻². The magnitude of the increase in gypsum application-induced rice yield increased with increasing soil pH. The gypsum rate and soil pH showed a positive interactive effect, whereby the increase in rice yield increased with the gypsum rate in the initial soils with pH ≥ 8.5 but remained stable at soil pH < 8.5. Gypsum application induced a reduction in CH₄ emissions with increasing gypsum application rate. Our results indicate that gypsum application could increase rice yield and reduce greenhouse gas emissions, providing a theoretical basis for evaluating the effects of gypsum application on high rice yield and mitigating global warming.

Study on ammonia reduction technology by manure surface acidification in animal housing

LIU Juan, WANG Xuan, CAO Yubo, BAI Zhaohai, MA Lin

2023, 31(2): 290-299. doi: 10.12357/cjea.20220538

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Animal housing plays an important role in NH₃ emissions from livestock, and in situ technology for NH₃ mitigation is lacking in China. Therefore, the aim of this study was to explore an efficient, economic, and practical technology to reduce NH₃ emissions from in situ animal housing. Here, we determined the effects of sulfuric acid and silage leachate at different doses on NH₃ emissions in a simulated experiment to select the best acidification conditions that could be applied to in situ NH₃ reduction technology in animal housing. We then designed and equipped a set of NH₃ mitigation technologies (an acid spraying device) in sheep housing and applied the selected acidification conditions to explore the effect of NH₃ mitigation technology on NH₃ emissions from the perspective of NH₃ reduction efficiency and economy. The results showed that sulfuric acid and silage leachate can reduce NH₃ emissions efficiently. The NH₃ reduction rates were 39.1% (P<0.05) for sulfuric acid and 42.7% (P<0.05) for silage leachate, respectively, when the spraying dose was 0.03 g·m⁻², but it only worked within 8 h. Because sulfuric acid is difficult to obtain on the market and atomizing silage leachate is challenging, lactic acid, the main component of silage leachate, was used as an acidifier in in situ housing. When spraying lactic acid at the dose of 0.03 g·m⁻² (0.01 mol·L⁻¹) three times per day (8:00, 16:00, 0:00) by using an acid spraying device, NH₃ reduction efficiency was the highest (55.6%, P<0.01); NH₃ concentrations in the daytime were reduced by 67.0% (P<0.01) (3 m height) and 72.0% (P<0.01) (0 m height), respectively, when acid was sprayed once per day at 8:00, but there was no influence on NH₃ concentration at night. When the acidification frequency was two times per day at 8:00 and 16:00, NH₃ concentration could be reduced throughout the day, and there was a more efficient reduction in the daytime with 72.0% (P<0.01) (3 m height) and 56.5% (P<0.01) (0 m height) than that in nighttime with 32.1% (P<0.01) and 25.8% (P<0.01) at 3 m and 0 m height, respectively. As for the cost of NH₃ reduction, spraying acid twice per day was the lowest at 147 ¥·kg⁻¹(NH₃), and the cost for three- and one-time acidification was 165 ¥·kg⁻¹(NH₃) and 211 ¥·kg⁻¹(NH₃), respectively. Infrastructure was the largest cost, accounting for approximately 80% of all costs. This study provides a feasible and efficient NH₃ reduction technology for in situ animal housing, but there is a need to improve the equipment cost for the wide promotion and application of this technology.

Multi-scenario land use change and its impact on carbon storage based on coupled Plus-Invest model

LUO Shuqi, HU Xiaomeng, SUN Yuan, YAN Cai, ZHANG Xin

2023, 31(2): 300-314. doi: 10.12357/cjea.20220520

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Land use/cover change (LUCC) is an important cause of carbon storage change in terrestrial ecosystems. Land use change is often constrained by policy, which affects carbon stock changes. To forecast the LUCC of Xi’an in 2030 under the guidance of the policy, and analyze its impact on carbon storage is of great significance for Xi’an policy-making, land use structure adjustment, and the realization of the “double carbon” goal. Based on the land use data (LULC) of 2000, 2010, and 2020, this study selected 11 driving factors and established three development scenarios of business as usual (Q1), ecological protection (Q2), and town development (Q3), respectively, according to the Xi’an “14th Five-Year Plan” policy planning. The PLUS model was used to predict and analyze the spatial distribution pattern of land use in Xi’an in 2030, and the InVEST model was coupled to evaluate the carbon storage of Xi’an in different development scenarios and analyze the change in carbon storage. The results show that: 1) the PLUS model has strong applicability in Xi’an City. The overall accuracy of the model was 0.93 and the Kappa coefficient was 0.89. 2) From 2000 to 2020, the areas of construction lands, grasslands and water bodies in Xi’an increased, while the areas of arable land, woodland, and wetland decreased. From the perspective of the transfer direction, arable land was mainly converted to construction land. 3) Q1 continued with the previous development pattern. In 2030, the quantity of ecological land, such as woodlands and water bodies, under Q2 increased compared with that in 2020, and the construction land areas under Q3 increased by 10.42%. 4) LUCC was the main reason for changes in ecosystem carbon storage. The total carbon storage under Q1 in 2030 decreased by 373.28 t compared with that in 2020, indicating that a continuation of the previous development mode would reduce the total carbon storage. Under Q2 in 2030, carbon storage increased by 564.73 t from 2020, which explains certain ecological protection measures to protect forest land, wetland, and increase the amount of cultivated land. This would also limit the transfer of ecological lands with high carbon density, such as cultivated land, into low carbon density land for construction purposes, potentially slowing the increasing trend of carbon reserves in terrestrial ecosystems. Under Q3, with the acceleration of urbanization, the scale of construction land has expanded, and a large number of urban areas occupy ecological and cultivated lands, which greatly reduces carbon storage. The results show that the major reason for the loss of carbon storage is the large expansion of construction land and the encroachment of ecological and arable land. The implementation of scientific and reasonable ecological protection measures can solve the carbon storage decline problem caused by economic development.

Long-term fertilization effects on soil aggregates organic carbon sequestration and distribution in a yellow-mud paddy soil

WANG Fei, LI Qinghua, HE Chunmei, WANG Ke, YOU Yanling, HUANG Yibin

2023, 31(2): 315-324. doi: 10.12357/cjea.20220307

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Agricultural management practices affect carbon sequestration in agricultural soils. This study was performed in southern China to investigate the effects of different fertilizations on soil aggregate organic carbon sequestration and distribution over time in yellow-mud paddy. There were four treatments: no fertilizer (CK), application of chemical fertilizer (NPK), combined application of chemical fertilizer and cattle manure (NPKM), and combined application of chemical fertilizer and straw (NPKS). After 36 years of the experiments (1983 to 2020), the soil samples were collected after rice harvest to analyze soil aggregate, organic carbon sequestration, and distribution. The results showed that macro-aggregates (>2 mm) and medium aggregates (0.25−2 mm) were major components of the bulk soil. Compared to CK, NPKM and NPKS significantly increased the proportions of macro-aggregates by 22.0% and 15.5%, respectively, but greatly decreased the proportions of medium aggregates (0.25−2 mm) by 14.3% and 10.2%, respectively (P<0.05). Application of fertilizer resulted in a significant increase in the organic carbon content of the bulk soil, ranging from 16.9% to 43.9%, compared with the CK treatment. The average organic carbon content of the macro-aggregates was 1.3–1.6 times that of the other aggregates. The organic carbon content of macro-aggregates (>2 mm), medium aggregates (0.25−2 mm), and silt and clay (<0.053 mm) was higher under NPKM than under CK. Furthermore, NPKS increased the organic carbon content of macro-aggregates (>2 mm) compared to CK. The macro-aggregate organic carbon content accounted for 44.5%−63.8% of the total soil organic carbon. Compared with CK, NPKM and NPKS treatments significantly enhanced macro-aggregate organic carbon sequestration by 25.0% and 19.3%, respectively; but decreased the organic carbon sequestration of medium aggregates (0.25−2 mm), micro-aggregates (0.053–0.25 mm), and silt and clay (<0.053 mm). For the macro-aggregates, the light fraction of organic carbon (LF-C) and mineral-associated organic matter (mSOC) were the major parts, and the proportions of mSOC accounted for 50.7%−57.7% of the macro-aggregates. Compared with CK, the content of LF-C increased by 20.7%−32.3% in the fertilization treatments, respectively, and the contribution of LF-C to total soil organic carbon was most significantly increased by 8.9% and 9.4% under the NPKM and NPKS treatments (P<0.05), respectively. For the medium aggregates, the organic carbon content of the fine fraction organic carbon was significantly higher under NPKM treatment than under other treatments (P<0.05); other sub-fractions was not affected by the application of fertilizer. The coarse fraction of organic carbon (CF-C) and mSOC were the major components of the organic carbon in medium aggregates. NPKM and NPKS significantly decreased the sequestration of LF-C, CF-C, and mSOC in medium aggregates compared with the NPK and CK treatments (P<0.05). The organic carbon content of the bulk soil was found to be significantly correlated with rice yield and organic input (P<0.01). Both macro-aggregate organic carbon content and LF-C content showed a significant positive correlation with rice yield (P<0.01). They were also significantly positively correlated with the organic carbon input (P<0.01). Overall, the combined application of chemical fertilizer with cattle mature or straw could increase the proportions and content of organic carbon of macro-aggregates, thus promoting the contribution of total soil organic carbon, especially with the application of cattle manure. Additionally, the combined application of chemical fertilizer and straw was beneficial in promoting macro-aggregate LF-C content and the contribution of total soil organic carbon. The organic carbon content and fractions of active carbon in macro-aggregates are closely related to the productivity of yellow-mud paddy soil. The results provide methods for fertilization management of yellow-mud paddy soil in southern China.

Effects of increased atmospheric CO₂ concentration and temperature on carbon and nitrogen metabolism in maize at the grain filling stage

WANG Jiao, LI Ping, ZONG Yuzheng, ZHANG Dongsheng, SHI Xinrui, YANG Jing, HAO Xingyu

2023, 31(2): 325-335. doi: 10.12357/cjea.20220395

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Abstract:
Future climate change will bring considerable challenges to agricultural production and food security. Presently, research on the effects of elevated CO₂ concentration and increased temperature on crops is mostly focused on C₃ crops, while research on C₄ crops is rare. Maize is the most widely planted C₄ crop in the world, it is of great significance to explore the response of maize to elevated CO₂ concentration, increased temperature, and their combination to assess the impacts of future climate change on C₄ crops. The maize variety ‘Xianyu-335’ was used. Four treatments were set up in controlled chambers: CK (CO₂ concentration 400 μmol·mol⁻¹, ambient temperature), EC (CO₂ concentration 600 μmol·mol⁻¹, ambient temperature), ET (CO₂ concentration 400 μmol·mol⁻¹, 2 ℃ higher than ambient temperature), and ECT (CO₂ concentration 600 μmol·mol⁻¹, 2 ℃ higher than ambient temperature). The related indices of photosynthetic physiology, glucose metabolism, and nitrogen metabolism of maize leaves were measured at the grain-filling stage, and the biomass of maize was measured after ripening. The results showed that: 1) under elevated CO₂ concentrations, the chlorophyll content, sucrose content, net photosynthetic rate, sucrose synthase activity, pyruvate kinase activity, and α-ketoglutarate dehydrogenase activity in leaves were significantly increased (P<0.05), while glutamate synthase activity was significantly decreased (P<0.05). Additionally, aboveground biomass and spike mass were significantly increased by 35.8% and 170.2%, respectively (P<0.05). 2) At increased temperatures, the net photosynthetic rate, and activities of sucrose synthase and pyruvate kinase of leaves were significantly increased (P<0.05), while α-ketoglutarate dehydrogenase and glutamate synthase activities were significantly decreased (P<0.05), and the above-ground biomass and the biomasses of leaf, stem, and spike were significantly decreased by 37.0%, 28.7%, 32.3%, and 62.2%, respectively (P<0.05). 3) Under the combination of elevated CO₂ concentration and increased temperature, the net photosynthetic rate and pyruvate kinase activity of leaves were significantly increased (P<0.05), whereas the chlorophyll content, and activities of α-ketoglutarate dehydrogenase and glutamate synthase were significantly decreased (P<0.05), and the leaf biomass was significantly decreased by 23.4% (P<0.05). In conclusion, elevated CO₂ concentration could alleviate the negative impact of increased temperatures on maize biomass by increasing photosynthesis and the activity of enzymes related to glucose metabolism and photosynthetic metabolites. Under elevated CO₂, increased temperature, or their combination, nitrogen metabolism in maize is inhibited; thus, leaves are subjected to nitrogen stress, which harms maize quality.

Response of deep soil CO₂ concentration to precipitation events in semi-arid areas

WANG Xiaolu, ZHANG Ning, HE Gaohang, LIN Xiaohua, CHEN Yan, WANG Rui, GUO Shengli

2023, 31(2): 336-344. doi: 10.12357/cjea.20220586

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Abstract:
In arid and semi-arid areas, soil moisture strongly influences the balance between respiration and diffusion, altering soil CO₂ concentration and surface flux. Numerous studies have focused on the relationship between surface soil CO₂ flux changes and rainfall events. Subsoil carbon constitutes a large fraction of the total carbon stock, but it is unclear how rainfall events influence subsoil CO₂ concentration dynamics. We continuously monitored CO₂ concentrations at 10, 50, and 100 cm in the soil profile from 2019 to 2021, and analyzed the various responses of subsoil CO₂ concentration to rainfall events. In this study, soil temperature showed apparent seasonal characteristics. As the air temperature changed, the soil temperature of different depths also changed from 100 cm < 50 cm < 10 cm to 10 cm < 50 cm < 100 cm. The soil moisture content of different layers was in the order of 10 cm < 100 cm < 50 cm, and a significant fluctuation was found at 10 cm. The soil CO₂ concentration gradually increased with the increase of the depth in the order of 10 cm < 50 cm < 100 cm, with mean values of 0.66×10⁴, 0.87×10⁴, and 1.04×10⁴ μmol∙mol⁻¹, respectively. On sunny days, the soil CO₂ concentrations at 10, 50, and 100 cm showed apparent diurnal variations and could be expressed as a single-peak curve. However, rainfall events significantly affected the change trends of CO₂ concentrations. Approximately 78% of the rainfall events quickly altered the soil CO₂ concentration in 10 cm layer. When the rainfall amount was exceeded 25 mm, the CO₂ concentration at 50 and 100 cm decreased after 91 and 121 hours. When the soil moisture status changed from drying to wetting phases under rainfall events, > 25 mm precipitation promoted an increase in soil CO₂ concentration at 10 cm by 30% which then began to decrease. The soil CO₂ concentrations at 50 and 100 cm decreased by 16.3% and 10.9%, respectively, with an increase in soil moisture. In arid and semi-arid areas, rainfall negatively affects the changes in soil CO₂ concentration at 10 cm depth under lower soil moisture content. This is because the decrease in gas diffusivity led to an increase in CO₂ concentration. Soil CO₂ concentrations at 50 and 100 cm depths decreased under rainfall events, although the soil moisture was higher than the field capacity. This was caused by the high soil moisture content, which inhibited microbial respiration. The responses of soil CO₂ concentration at different depths to rainfall differed and largely depended on the soil moisture content.

Current Issue 2023, Volume 31, Issue 2

Current Issue
2023, Volume 31, Issue 2