Organic structure and possible origin of ancient charred paddies at Chuodun Site in southern China

Abstract

A number of ancient charred paddies with a 14 C dating of about 5900 a BP were recovered in the sixth excavation at Chuodun Site and are assigned to the Majiabang culture (7-6 ka BP). To understand their formation mechanism, the ancient charred paddies were compared to modern paddies using FT-IR spectrum and thermaogravimetric analysis. At the same time, modern charred paddies were made in helium by the laboratory method, and the structural characteristics of them and the ancient ones were revealed using CP/MAS-13 C-NMR. Our results show there are more aromatic moieties in ancient charred paddies compared to modern paddies. The aliphatic components of modern charred paddies decrease continuously, accompanied by the accumulation of aromatic components, when the duration and temperature of oxidation increase, and the structure buildings of modern charred paddies are more similar to ancient ones. Given the planting manner of paddies during Majiabang culture period, these ancient charred paddies might be a result of the original farming mode involving fire. ancient charred paddies, FT-IR, TGA, CP/MAS-13 C-NMR, formation mechanismArchaeologists have discovered many ancient agriculture sites in the Yangtze River Delta during the past few decades [1,2] . Based on the ridges and ditches of ancient paddy fields and the pollen, phytolith and fossil paddy found at these ancient agriculture sites, as well as relevant ancient farming implements, scholars have characterized the paleosols of these ancient agriculture sites as ancient paddy soils (APS). From 1998 to 2003, five excavations were conducted at Chuodun Site and abundant cultural artifacts unearthed such as ceramic ware and pottery basins, as well as some ancient charred paddies (ACP) [3,4] . The Chuodun Site's bearings on studies of other facets such as the pedology and environment were ignored because the early research only limited its field to archaeology. In order to explore the extensive values of Chuodun Site, the sixth excavation for multi-disciplinary studies was carried out by scientists from various fields of study at the end of 2003. The main achievements include new pedological and palynological evidence showing the existence of APS at Chuodun Site as well as recognition of Xiashu loess as their parent material [5][6][7] . In addition, the study on fertility characters of APS demonstrated that the planting of ancient paddies facilitated the increase of bioelements such as C, N, P and S; however, the microbiological analysis concluded that modern paddy soils (MPS) and APS possessed different dominant methanogenic ancient bacteria species [8,9] . In environmental aspect, main researches were done on the distribution properties and origin of the polycyclic aromatic hydrocarbons (PAHs) in the profiles of APS, and it was found that the content of PAHs were higher than that in arid land and bottom soils [10,11] .During the sixth excavation, 22 more paddy fields were found. The ACP collected all had that charred characteristic as well as an age of about 5900 a ...

Biochar stability in soil: meta‐analysis of decomposition and priming effects

“…Oxygen depletion contributes to the increased MRT of biochar in waterlogged ecosystems such as sediments and paddy soils (Knicker, 2011). For example, the formation of a high content of aromatic and carboxyl C in ancient Chinese paddies is attributed to the cultivation mode of paddies involving fire under drying-rewetting alternation conditions (Cao et al, 2006;Hu et al, 2009).…”