Millet-wheat-based agricultural system formation in the North China Plain during the late warring states period by stable isotope analysis

To demonstrate the contribution extent of wheat-based food to the human diet in a millet-based agricultural region, 15 human bones and 35 animal bones, respectively, from the Bairencheng site in Xingtai, Hebei, China were selected for stable isotope analysis. Animal isotopic data indicated that most terrestrial fauna (delta 13C value range: -17.7 %o - -7.6 %o, mean f SD value: -13.4 f 2.8 %o; delta 15N value range: 4.4 %o - 10.4 %o, mean f SD value: 7.5 f 1.6 %o, n = 35) had a dietary pattern of mixed C3/C4-based food. Human isotopic results obtained by direct AMS-14C dating (2350 cal. a BP - 2146 cal. a BP) show that the diet of past populations (delta 13C value range: -16.3 %o - -12.6 %o, mean f SD value: -14.6 f 1 %o; delta 15N value range: 7.2 %o - 9.8 %o, mean f SD value: 8.7 f 0.9 %o, n = 14) also exhibited a feature of mixed C3/C4-based foods. The isotopic fractionation effect between humans and fauna indicates that the past populations mainly consumed mixed C3/C4 plant-based food. Historical records and archeological data show that C4-based food mainly consisted of millet, whereas C3-based food mainly consisted of wheat, which indicates that a millet-wheat-based agricultural system formed in the North China Plain during the late Warring States Period. Compared with stable isotopic data of humans from contemporaneous and adjacent archeological sites, wheat-based food had greater contribution to past populations at the Bairencheng site. Wheat-based agriculture developed rapidly under a millet-based agricultural system, and wheat became an important food resource for the past populations in the North China Plain during the late Warring States Period.