Identifying prehistoric irrigated rice fields and characterizing the beginning of paddy soil development are important for a better understanding of human development and agricultural history. In 2003, paddy soils and irrigated rice fields buried at a depth of 100-130 cm were excavated at Chuo-dun-shan in the Yangtze River Delta, close to Suzhou, China. The fields of sizes between 1.4 and 16 m(2) were surrounded with ridges that were connected to ditches/ponds via outlets to control the water level within the fields. Many carbonized and partly carbonized rice grains with an age of 3,903 B.C. (measured (14)C age 5,129+/-45 a BP) were recovered. The surface layers of these buried paddy fields showed a high content of soil organic matter and a considerable high density of rice opals. The latter were identified to derive from Oryza spp. Solid-state (13)C nuclear magnetic resonance spectroscopy revealed aromatic carbon (C) as the predominant organic C form in the fossil surface layer. This is expected, if the major source represents burnt rice and straw. In summary, our data are in agreement with new evidences indicating that in China, paddy soils and irrigated rice cultivation were initiated and developed more than 6,000 years ago.

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Pollen and phytolith analyses were undertaken at the Jiangli site in Suzhou, Jiangsu Province, combined with studies on macrofossils by flotation. The concentration of pollen decreased while the percentage of Poaceae pollen in the profile increased from the late phase of the Majiabang Culture to the Songze Culture suggesting that human impact on the local environment intensified gradually. The discovery of rice paddy implies a relatively advanced rice cultivation in this area during the middle-late Holocene. Other than phytoliths, the high percentage of Oryza-type Poaceae pollen (larger than 40 µm) supplied robust evidence for the existence of rice paddy. Moreover, the fact that the farther from the rice paddy, the lower the concentration and percentage of Poaceae pollen also proves that the dispersal and deposition of pollen is inversely proportional to the distance.

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