Phytolith evidence for crop structure at the Zhangwangzhuang site during the early and middle Yangshao cultural periods on the southwestern Huanghuai Plain, China

The southwestern Huanghuai Plain, located in the transitional climate zone between southern and northern China, was characterized by a unique rice-millet mixed farming pattern during the Neolithic period, which laid a solid economic foundation for the origin of civilization in Central China. However, the specific formation time and evolution of mixed farming in this area are still unclear. In this study, phytolith analysis was conducted on 31 sediment samples from Zhangwangzhuang, a site that has been dated back to the early and middle Yangshao cultural periods (ca. 6.3–5.6 ka BP) in the research area. The results indicate that the mixed farming of rice and millets appeared at Zhangwangzhuang since the early Yangshao period (EYS), approximately 6.3 ka BP. Further quantitative analysis of the phytolith data shows that broomcorn millet (Panicum miliaceum) and rice (Oryza sativa) were abundant at Zhangwangzhuang. Notably, the proportion of rice declined greatly in the second phase and afterward increased continuously from the third to the fourth phases, which was much higher than that of nearby contemporary sites and might be attributed to the abundant water resources around Zhangwangzhuang. Combined with the existing archaeobotanical data, this paper argues that the emergence of millet cultivation during the early Yangshao cultural period in the research region could be caused by the southward spread of the Yangshao culture. On the other hand, millets became more widely cultivated in the southwestern Huanghuai Plain since 6.0 ka BP, which could have been caused by climate change, from warmth and humidity to coolness and drought. The paper thus provides important information regarding the formation and developing process of rice-millet mixed farming in the southwestern Huanghuai Plain, contributing to a better understanding of the subsistence strategy adopted by the local people when facing climate change in the north–south transitional zone of China.