Spatiotemporal dynamics of China’s cropland carbon budget from 2000 to 2020: incorporating harvested carbon and straw return

Agroecosystems play a crucial role in regulating the terrestrial carbon cycle, especially in China where there are about 128 million hectares of cropland, accounting for about 10% of the global cropland area. Previous regional-scale studies have primarily used net ecosystem production (NEP) to represent cropland carbon uptake, whereas carbon export through crop harvest has received less attention when assessing the overall cropland carbon budget. Moreover, because straw return can retain part of the harvested carbon within cropland ecosystems, the net carbon balance may vary with the extent of straw return. Therefore, this study aimed to characterize carbon dynamics in China’s croplands by estimating net biome production (NBP) under three straw return scenarios, including no return, full return, and regionally differentiated return practices. During 2000–2020, the mean NEP of China’s croplands was 185.5 ± 300.8 g C m −2 yr −1 . After integrating pixel-level NEP estimates over the harvested cropland area, the national cropland NEP was estimated at 157.4 ± 22.9 Tg C yr −1 , whereas total HC reached 518.6 ± 90.5 Tg C yr −1 . Overall, the cropland ecosystem acted as a carbon source in all three scenarios, with national totals of −361.3 ± 69.4 Tg C yr −1 (no straw return), −135.8 ± 31.9 Tg C yr −1 (full straw return), and −233.8 ± 48.3 Tg C yr −1 (regionally differentiated straw return). In addition, both NEP and HC exhibited increasing trends from 2000 to 2020 despite a declining NBP trend due to a higher increasing rate of HC. China’s croplands functioned as a net carbon source when crop harvest was considered during 2000–2020. This study provides a comprehensive assessment of China’s cropland carbon budget by taking into account impacts of harvest and straw‑return practices. The findings improve understanding of the spatiotemporal dynamics of cropland carbon budgets and provide scientific evidence to support carbon management strategies for sustainable agriculture.