Investigation of surface soil Phytoliths in Upland Rice Fields of Southern China

Background and Aims Upland rice is a distinct ecotype of rice that does not require irrigation, grows only on natural precipitation, and is widely distributed in subtropical hilly areas. Research on the origin and dispersal routes of upland rice is limited, and identifying rice crop remains in archaeological sites is critical for providing associated information. Methods In this study, phytolith analysis methods, including phytolith assemblages, sensitive to fixed phytolith types, and fish-scale decorations on rice bulliform phytoliths, were performed on 66 surface soil samples collected from upland rice fields at nine locations in Yunnan, Guangxi, Guizhou, and Fujian. Results Results showed that surface soil phytolith assemblages of upland rice fields were mainly composed of bilobate (37.12% ± 6.25%), smooth elongates (23.56% ± 4.67%), short saddles (12.78% ± 4.13%) and motor cell phytoliths (10.80% ± 3.71%), which differed substantially from assemblages found in lowland rice and wild rice habitats. The ratio of sensitive to fixed phytolith types, which reflects wet-dry environmental changes, was measured at 0.47 ± 0.16. This value is lower than those found in lowland rice paddies and wild rice habitats. The proportion of rice bulliform phytoliths with ≥ 9 fish-scale decorations was 23.72% ± 6.80% in upland rice fields, lower than that in lowland rice paddies, but slightly higher than that in wild rice habitats. Conclusion The findings highlight the potential of using variations in the number of fish-scale decorations on rice bulliform phytoliths, along with phytolith assemblages, to identify and differentiate rice cultivation practices at archaeological sites effectively.