Four pathways towards carbon neutrality by controlling net greenhouse gas emissions in Chinese cropland

Highlight

• Four feasible pathways towards carbon neutrality in Chinese cropland were proposed.

• GHG emissions were projected to be 439.9–443.5 Tg CO₂e after 2030 in baseline.

• GHG emissions would decline to 338.3 Tg CO₂e in 2060 by implementing the four pathways.

• Accumulated soil C sequestration would increase by 1766.2 Tg CO₂e compared to baseline.

• Cropland could achieve a net GHG reduction of 41.2% in 2060 while ensuring food security.

Abstract

Decreasing greenhouse gas (GHG) emissions and enhancing soil carbon (C) sequestration in cropland are necessary to achieve carbon neutrality at national scale. However, feasible pathways to mitigate net GHG emissions in Chinese cropland while ensuring food security remain poorly defined. Here, we establish a comprehensive assessment framework and propose four mitigation pathways. In the baseline scenario, GHG emissions are projected to be 439.9–443.5 Tg CO₂e after 2030. Through simultaneously implementing the four pathways of recycling organic waste, improving nitrogen (N) use efficiency, optimizing water management and strictly controlling N input/surplus, cropland GHG emissions are projected to decline from 433.5 Tg CO₂e in 2020 to 389.7 Tg CO₂e (-11.4%) in 2030 and 338.3 Tg CO₂e (-23.7%) in 2060. The accumulated quantity of soil C sequestered would increase by 33.9% from 2021 to 2060. Considering both GHG emission reduction and increment of soil C stocks, the net GHG reduction rate would be 37.4% and 41.2% in 2030 and 2060, respectively. These pathways help transition crop production to a low-carbon and high-efficiency pattern while maintaining or increasing crop yield. As the first attempt, our study provides a scientific reference for approaches to accelerate GHG mitigation and soil C sequestration in Chinese cropland. This type of integrated assessment has potential to support policy-making in developing countries aimed at finding an equitable balance between crop production and environmental benefits.

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.