Abstract
A joint research project has been carried out between Japan and China on the origin and spread of rice in the Middle and Lower Changiiang River Valley of China by plant opal analysis since 1992. The excavation of ancient paddy fields near the Caoxieshan site in Wu County, Jiangsu Province was conducted. Ten accumulated soil layers with each cultural period property were confirmed, and the layers from the fifth layer to the tenth layer were identified as belonging to the Middle Majia-bang period (B.P.5900-6200). And the existence of paddy fields in soil layers of Chunqiu, Songze and Majiabang period were identified by plant opal analysis. Moreover, more than forty paddy field sites were excavated under the ninth or tenth layer. This paper reports on the results of quantitative and morphological analysis of plant opals on soil samples collected from nineteen paddy filed sites and ten soil layers at the Caoxieshan site in 1994 and 1995, and discusses the cultivar group and its historical change of ancient rice cultivated near the Caoxieshan site. The quantitative analysis of plant opals detected large amounts of rice plant opals from motor cell silica bodies in all the samples, suggesting that the rice cultivation near the Caoxieshan site began from the middle Majiabang period and continued up to the present. Moreover, the rapid increase of rice leaf weight inferred from plant opals in soil layers of middle Majiabang period suggested that rice cultivation had been prevalently practised during this period. The morphological analysis of plant opals suggested that the plant opals from the soil layers of middle Majiabang period were derived from japonica rice. Compared to the motor cell silica bodies from Chinese native Keng (correspond to japonica) rice, the plant opals had a larger value in b/a as well as in vertical length and lateral length, and the discriminant scores were more like those from typical japonica rice. A comparison of the discriminant scores of plant opals from the ten soil layers showed a slowly decreasing trend from the lower layers to the upper ones. And the scores were especially small for the soil layers above the third one (the Song period), suggesting that it is highly possible that the indica rice would be probably cultivated from Song period near the Caoxieshan site.
