An adequate food supply is a core issue for sustainable development worldwide. Amid greater instability in the food supply triggered by more armed conflicts, trade disputes, and climate change, a decline in grain cultivation area still plagues many regions. China, a major food producer globally, is a case in point. The truth is that at the moment, the formulation and implementation of policies as well as academic discussions regarding this issue are predominantly based on the sown area of grains, overlooking the fundamental role co-played by population, yield efficiency, and sown area in determining food supply. Furthermore, the commonly used indicator, the non-grain cultivation rate, fails to directly reflect the impact of the phenomenon on the grain supply. To address these gaps, this study introduces trend-change detection and factor-contribution analysis, uses long-term grain sown area data to identify regions with significant grain retreat, and quantifies the relative influence of population shifts, crop yield improvements, and sown area changes on food supply. Key findings include the following: China’s total grain production maintained steady growth from 2003 to 2023, far exceeding conventional food security thresholds. Temporary reductions in grain sown area (2015–2019, 2021–2022) were offset by rising yields, with no substantial decline in supply. Twelve provinces/municipalities, Beijing, Shanghai, Zhejiang, Fujian, Guangdong, Guangxi, Guizhou, Shaanxi, Ningxia, Sichuan, Chongqing, and Hainan, exhibited substantial declines in grain plantation. However, Sichuan and Shaanxi achieved counter-trend growth in food supply, while Ningxia and Guizhou experienced frequent fluctuations. The sown area was not always the dominant factor in per capita grain availability. Yield increases neutralized cropland reduction in Sichuan, Shaanxi, Guizhou, and Ningxia, whereas population inflows outweighed the sown area effect in the other eight provinces. The study concludes that China’s grain cropland reduction has not yet posed a threat to national food security. That said, the spatial concentration of these affected regions and their ongoing output reductions may raise domestic grain redistribution costs and intensify inter-regional conflicts over cropland protection. Meanwhile, population influx plays a similarly important role to that of grain plantation decline in the grain supply. Considering that, we believe that more moderate measures should be adopted to address the shrinkage of grain planting areas, with pre-set food self-sufficiency standards. These measures include, but are not limited to, improving productivity and adopting integrated farming. Methodologically, this work lowers distortions from normal annual cropland fluctuations, enabling more precise identification of non-grain production zones. By quantifying the separate impacts of population, crop yield, and sown area changes, it supplements existing observations on grain cropland decline and provides better targeted suggestions on policy formulation and coordination.

Abandoned cropland is a widespread issue globally, with the impacts of utilizing abandoned cropland, such as grain production and carbon emissions, raising increasing concern. However, existing studies have largely overlooked the potential spillover effects on other regions through grain flows when increasing grain production in one region by utilizing abandoned cropland. Therefore, this study aimed to comprehensively estimate the impacts of using winter fallow fields (a typical seasonal abandoned cropland) on grain production and carbon emissions, particularly its neglected spillover impact. Focusing on Zhejiang province, this study used remote sensing techniques to identify winter fallow fields in 2018 and then assessed the impact of using those winter fallow fields on grain production based on grain yield data from the FAO, as well as its local and spillover impacts on carbon emissions based on the Greenhouse Gas Emission Factor method and a transportation carbon emission model. The results indicate the following: (1) The winter fallow fields in Zhejiang cover 5,161,000 hectares, accounting for 40.8% of the total cropland, with a notable prevalence in Jiaxing, Huzhou, Jinhua, and Quzhou. (2) Using winter fallow fields would increase grain production by 1,870,000 tons. (3) At the same time, local carbon emissions would rise by 261,000 tons if using winter fallow fields, but this would be paired with a reduction of 668,000 tons of carbon emissions from other regions (that is, a spillover impact), reflecting a net reduction (−447,000 tons) in overall emissions. In conclusion, using winter fallow fields can achieve a ‘win–win’ effect, increasing grain production while reducing carbon emissions. This study highlights that the spillover effects of using winter fallow fields on carbon emissions significantly surpass the localized impact, underscoring a critical aspect that has been traditionally undervalued, which should be paid more attention when policymakers formulate and implement cropland use policies. This study not only contributes to the academic discourse on sustainable land management but also serves as a practical guide for policymakers seeking to optimize agricultural productivity while curtailing the carbon footprint, thereby advancing towards a more secure and environmentally responsible food system.