Stable isotopic analyses of the remains of plants that have been unearthed from archaeological sites are often featured as key indicators of crop cultivation and the living environment. However, systematic archaeobotanical studies have not been applied widely in Chinese historical sites, especially in those from the Tang dynasty. This paper aims to use carbon and nitrogen isotopic analyses to reveal the potential influence of water and fertilizer conditions on the size of millet chaffs that were excavated from the Chashancun cemetery. To achieve this, >3600 uncharred broomcorn and foxtail millet chaff remains were measured. Furthermore, 30 broomcorn millet samples and 30 foxtail millet samples were selected to analyze the carbon and nitrogen isotopes, respectively. The widths and thicknesses of the broomcorn millet chaffs ranged from 1.11 to 2.38 mm and from 0.95 to 2.24 mm, respectively, while those of the foxtail millet chaffs ranged from 0.95 to 1.94 mm and from 0.69 to 1.90 mm, respectively. The δ¹³C and δ¹⁵N values of the broomcorn millet chaffs ranged from −13.0‰ to −12.0‰ and from 15.7‰ to 17.8‰, respectively, while those of the foxtail millet chaffs ranged from −14.0‰ to −12.9‰ and from 15.7‰ to 18.8‰, respectively. The results show correlations between the millet chaff size and the carbon/nitrogen isotopic values, suggesting that water and fertilizer conditions might have significantly affected millet grain yield during the late seventh century in northwestern China.

Broomcorn millet (Panicum miliaceum) is among the earliest domesticated staple crops in the world’s agricultural history and facilitated the development of several early agrarian cultures, particularly those originating in northern China. However, the propagation route of broomcorn millet in China from the Middle Ages to the present remains unclear. The aim of this study is to explore the genetic affinity between ancient and modern millet samples, trace the genetic origins and diffusion pathways of broomcorn millet, and provide insights into its domestication and spread. To achieve this, we sequence ancient DNA from broomcorn millet remains excavated from the Chashan Village cemetery (AD 691) in Gansu Province, China. Phylogenetic and population genetic analyses, integrating ancient and modern millet genomes, reveal a close genetic relationship between ancient millet and contemporary millet from Ningxia Province (445 km away from Chashan Village), suggesting a potential origin for the Chashan millet. This finding aligns with the tomb’s epitaph, which documents the reburial of the tomb’s owner, who was originally buried in Ningxia, and provides important archaeological evidence for understanding the interaction between geopolitical dynamics and the natural environment in northwest China during the late seventh century. Furthermore, outgroup-f3 and D statistics evidence suggests substantial genetic interactions between ancient millet and modern varieties from the Loess Plateau, Huang-Huai-Hai Plain, and Northeast Plain, indicating the dispersal route of broomcorn millet, along with human migration routes, from the northwest to northern China and ultimately to the northeast region, starting from the Middle Ages onward. This study enhances our understanding of millet’s genetic history, offers a novel perspective on burial archaeology, and provides valuable insights into the origins, domestication, and diffusion of broomcorn millet.

The spatio-temporal evolution of human subsistence strategies and their driving force in prehistoric Eurasia has received increasing attention with the rapid development of archaeobotanical, zooarchaeological, and isotopic research in recent decades, while studies focusing on the historical periods are relatively absent. In the Hexi Corridor in northwestern China, which has served as a hub for trans-Eurasian exchange since the late prehistoric period, archaeobotanical data have been reported from numerous Neolithic and Bronze Age sites, as well as sites from the Wei and Jin Dynasties (220–420 BCE) to the Yuan Dynasty (1271–1368 BCE). However, no archaeobotanical study has been conducted at sites of the Han Dynasty (202 BCE–220 CE), a crucial period connecting prehistoric and historical eras. In this study, we identified 32475 plant remains, including 31,463 broomcorn millets, 233 foxtail millets, and 780 weeds, from the Shuangdun North Beacon Tower (SDNBT) site of the Han Dynasty at the western end of the Hexi Corridor, suggesting that millets played a prominent part in human subsistence strategies in the area during this period. In addition, sheep, chicken, dog, horse, and rodent remains were also collected at the site. By applying a multi-disciplinary approach, we detected a remarkable change in plant-based subsistence in the ancient Hexi Corridor. Specifically, the importance of millet crops, compared with other crops (especially barley and wheat), in plant-based subsistence declined from the Late Neolithic to the Bronze Age; it apparently improved during the Han and Sui-Tang Dynasties (581–907 CE), when agricultural empires controlled the area, and then declined again during the Wei, Jin, Northern, and Southern Dynasties (220–581 CE) and the Song-Yuan Dynasty (960–1368 CE), when nomadic regimes controlled the area. Climate change, trans-Eurasian exchanges, and geopolitical shifts influenced the diachronic change in plant-based subsistence from the Late Neolithic to the historical periods in the Hexi Corridor.