Four pathways towards carbon neutrality by controlling net greenhouse gas emissions in Chinese cropland
Graphical abstract
Introduction
Cropland is a major emission source of greenhouse gasses (GHGs), generating nearly 8% and 32% of global anthropogenic emissions for methane (CH4) and nitrous oxide (N2O), respectively (Saunois et al., 2020; Tian et al., 2020). Soil carbon (C) sequestration in cropland is a non-negligible carbon sink, which contributes to mitigating climate change and increasing crop productivity (Lal, 2004; Schlesinger and Amundson, 2019). Reducing agricultural GHG emissions and increasing soil C sequestration are both necessary to achieve global targets to limit warming (Wollenberg et al., 2016). With increasing future population and food demand, the balance of GHG emissions, C sequestration and food security is a key challenge in agricultural development worldwide.
Carbon neutrality is a bold ambition for the future global governance of climate change. China has committed to peak carbon dioxide emissions before 2030 and to achieve carbon neutrality before 2060 (Ministry of Ecology and Environment, 2021). To achieve these goals, emissions need to be cut in all sectors, including agriculture. China uses only 7.5% of the world's arable land to feed 19.5% of the global population, and ranks top in the world for production of wheat, rice, and most types of vegetable and fruit (Huang and Yang, 2017; FAO, 2021). Unsustainable agricultural managements and excessive use of chemicals in crop production have been major concerns in recent decades due to their large GHG emissions and other environmental costs (Nayak et al., 2015; Hong et al., 2021; Zeng et al., 2021). GHG emissions in cropland, mainly including N2O emissions from fertilized soil and CH4 emissions from rice paddy, accounted for 59% of total agricultural emissions in China (Ministry of Ecology and Environment, 2018). Soil C sequestration in cropland contributed to 12% of national terrestrial C sink and was considered a nature-based solution to tackle climate change (Fang et al., 2018; Yang et al., 2022). Practices targeted GHG emission reduction and C sequestration in crop cultivation must have no adverse impacts on food security. The Chinese government now places high priority on green and low-carbon agricultural development, and has issued a series of laws and regulations, and implemented actions to promote environmentally friendly and sustainable agricultural practices (Ministry of Agriculture and Rural Affairs, 2015a; Shen et al., 2013; Guo et al., 2020; Smith, 2020). Significant advances have been made in agricultural GHG reduction and soil C increase through adoption of clean technologies, water-saving irrigation and fertigation, soil testing and formulated fertilization, reducing chemical fertilizer application, enhancing manure management and crop residue return (Teng et al., 2019; Shen et al., 2020; Zhang et al., 2021). However, continued increases in living standards and changing nutrition demand in the future will require continued increases in grain yield and improvements in food quality, which may present challenges to agricultural GHG reduction in China. There are often trade-offs among the objectives of GHG mitigation, C sequestration, efficiency and productivity in crop production (Maraseni et al., 2020). How can China peak GHG emissions in cropland while ensuring food security and nutrition supply, and what is the potential for GHG reduction and C sequestration? While there have been numerous studies estimating GHG emissions and specific mitigation options with some analysis at national scale (Wang et al., 2014; Xia et al., 2016; Shang et al., 2021; Han et al., 2021), there has been no previous systematic analysis of these issues in the context of China's emission peaking and carbon neutrality targets.
To fill this knowledge gap, we developed an integrated assessment framework for GHG mitigation and soil C sequestration from 2021 to 2060 in China's cropland. The framework is comprised of four components: (1) selection of available mitigation options that do not decrease crop yield and that are feasible for farmers to adopt; (2) set-up of mitigation scenarios based on existing policies, strategies and plans; (3) projection of activity data based on assumptions about population, grain and meat demand, and choice of emission factors applicable to the selected mitigation options; and (4) estimation of GHG emission, C sequestration and emission reduction potential. We consider direct GHG emissions in cropland due to application of synthetic fertilizer, organic fertilizer and crop residue management, as well as indirect GHG emissions due to nitrogen (N) deposition, leaching and run-off. Using data integration and scenario analysis, this study aims to outline feasible pathways to mitigate GHG emissions and promote C sequestration in China's cropland at national scale from 2021 to 2060. The results may serve as a reasoned basis for low-carbon crop production and can be used to support decision-making in pursuit of the dual goals of carbon neutrality and food security in China.
Section snippets
Selection of available mitigation options and set-up of scenarios
To identify available options for GHG emission reduction and C sequestration in China's cropland, all current mitigation practices assessed in published literature or recommended in national policies were reviewed. Four criteria were considered for the selection of mitigation practices, as follows.
- (1)
Effectiveness: Practices with evidence of effectiveness in reducing GHG emissions and/or enhancing soil C sequestration were included, and the literature must have shown that these effects were
Results
In the baseline scenario, GHG emissions in cropland were projected to slightly increase at an average rate of 0.12 Tg CO2e year–1 from 2021 to 2060, and to maintain a stable level (439.9–443.5 Tg CO2e) after 2030 (Fig. 1). Emissions from rice, maize, wheat, vegetables and fruit accounted for 35.4%−42.6%, 9.2%−12.9%, 5.1%−5.6%, 9.1%−11.1% and 5.4%−6.5% of total emissions, respectively. The accumulated quantity of soil C sequestered in cropland from 2021 to 2060 was 5212.1 Tg CO2e, and the C
CH4 and N2O reduction, C sequestration and co-benefits of the four pathways
Our study estimated historical GHG emissions in Chinese cropland from 1990 to 2020 using country-specific emission factors, and presented a first attempt to derive realistic pathways for net GHG mitigation from 2021 to 2060 using various necessary data and assumptions. The total N2O and CH4 emissions we calculated based on historical statistics were similar to the estimation reported in the National Communication on Climate Change of China (Ministry of Ecology and Environment, 2018). According
Conclusion
This study comprehensively estimates, using data integration and scenario analysis, the potential for reduction of GHG emissions and increases in soil C sequestration in Chinese cropland from 2021 to 2060 under four realistic pathways in the context of the national carbon neutrality target. GHG emissions are projected to be 439.9 Tg CO2e in 2030 and 443.5 Tg CO2e in 2060 in the baseline scenario. Our results indicate that national GHG emissions from cropland could peak before 2030 if any of the
CRediT authorship contribution statement
Bin Wang: Writing – original draft, Writing – review & editing, Formal analysis, Investigation. Andong Cai: Data curation, Formal analysis. Yu'e Li: Conceptualization, Writing – original draft, Formal analysis, Supervision, Project administration. Xiaobo Qin: Data curation, Formal analysis. Andreas Wilkes: Writing – review & editing. Panlei Wang: Data curation, Formal analysis. Shuo Liu: . Xiaoquan Zhang: Conceptualization, Formal analysis. Nan Zeng: Conceptualization, Formal analysis.
Declaration of Competing Interest
The authors declare no competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This research was supported by the projects of technologies and pathways for agricultural GHG mitigation and carbon sequestration funded by MARA, PRC (Grant No. 13210352) and the National Natural Science Foundation of China (Grant No. 41905102).
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