How did trans-Eurasian exchanges affect spatial-temporal variation in agricultural patterns during the late prehistoric period in the Yellow River valley (China)?

The introduction of wheat into China between ~4500 and 4000 cal. a BP is thought to have restructured the ancient Chinese agricultural system and contributed to the formation and development of Chinese civilization. However, the spatial variation in agricultural development before and after the introduction of exotic crops across the Yellow River valley has not yet been discussed in detail. Here, we report new archaeobotanical data and radiocarbon dates from 25 sites in Sanmenxia, Henan Province, which was a hub for human migration in the middle reach of the Yellow River. Integrating our data with those of other archaeobotanical studies in northern China confirms that spatial cropping patterns in the Yellow River valley changed significantly around 4000 cal. a BP in the context of trans-Eurasia exchanges. From 7000 to 4000 cal. a BP, millet crops in the upper and middle Yellow River valley dominated the agricultural system, while mixed millet and rice agriculture developed in the lower Yellow River valley. In the subsequent period (4000–2200 cal. a BP), the cropping system in the upper Yellow River valley changed predominantly to barley and wheat agriculture, supplemented with millets. The contemporaneous cropping system in the middle and lower Yellow River valley, however, was dominated by millets, supplemented with wheat and rice. We argue that technological innovation and its dissemination in the context of trans-Eurasian cultural exchanges provided the basis for changes in the agricultural systems in northern China during the Bronze Age. Additionally, the trajectory of agricultural development was influenced by the natural environment and social change in different regions of the Yellow River valley. [ABSTRACT FROM AUTHOR]