Millet stable isotopes reveal the advance of agricultural practices in the core political regions of early imperial China

Recent archaeological research has revealed a significant intensification of agricultural practices in prehistoric China. Traditional historical perspectives suggest that the Han Dynasty also saw notable advancements in agriculture, though supporting evidence from archaeological science, along with comparative studies of farmland management practices between these two critical periods, remains limited. Here, we analyzed carbon and nitrogen stable isotopes from common millets (Panicum miliaceum) and foxtail millets (Setaria italica) recovered from four Han Dynasty tombs (Longzaocun, 2002CSX, 2008XJG, and Sanyaocun) and one Late Neolithic site (Ziweitianyuan) in the Guanzhong Basin, Central China. Our results integrate previously published millet isotope data spanning the Late Neolithic to Han Dynasty, reveal a long-term trajectory of agricultural management practices in the Guanzhong Basin under changing climatic conditions from about 3625 BCE to AD 220. Compared to the Late Neolithic period, the δ¹³C values of common and foxtail millets in the Han capital and its surrounding areas decreased by 3.4 ‰ and 3.8 ‰, respectively, while the δ¹⁵N values increased by 6.5 ‰ and 2.7 ‰, indicating an intensification of fertilization strategies. Combined with historical records, this study provides direct evidence of how farmland management in the Han Dynasty maintained soil fertility and agricultural productivity in response to the progressively arid and cold climate of the Holocene, thereby deepening our understanding of soil memory.