| Highly contained in soil, the forms of iron are changeable in soil forming process under the influence of environment. Affected by frequent redox processes, the shapes of paddy soil continue to transform. It is still not clear how iron in buried ancient paddy soil has transformed its form since it has lied underneath modern soil for an extended time. Therefore, this program takes the buried ancient paddy soil of Shanlonggang Village Site, Liyang Plain, as research objective; conducts research on the features of iron in ancient paddy soil; analyzes the content and form of iron with various sizes of soil aggregates and discusses the infrared spectrum of iron oxide in ancient paddy soil. Main results for this study are as follows:(1) The explicit variation of the different form Fe was observed in buried ancient paddy soil in Liyang Plain, for 33.97-46.88 g/kg in total iron,11.10-20.36g/kg in free iron, 2.64-3.35 g/kg in amorphous iron and 8.46-17.43g/kg in crystal iron. Apart from amorphous iron, proportions of all others in buried ancient paddy soil outnumber those in modern paddy soil. Irons of various shapes in buried ancient paddy soil hold the features of eluviation and deposition. Distribution variation of different Fe form was observed and the relative enrichment of Fe characterized obviously in buried ancient paddy soil.(2) In buried ancient paddy soil aggregates, besides amorphous iron, others present principally in macro aggregates of ancient paddy soil, and the content is likely to surpass modern paddy soil; or (5-2mm)> (2-1mm)>(1-0.25mm)> (<0.25 mm). Macro aggregates eye high freeness and cryogel grade, which is on the contrary of activation grade. Free iron, crystal iron, freeness and cryogel grade go uplifted in line with soil depth; which amorphous iron and activation grade performs oppositely. In modern paddy soil, free oil, amorphous iron, crystal iron, freeness and cryogel grade increase along with soil depth.(3) The results of Tessier Method show that, Iron mainly exists in organic (OM-Fe), oxide (OX-Fe) and residual (RES-Fe) forms in buried ancient soil, which accounts for 99.9% of total iron. Iron in water-soluble (WS-Fe) and exchangeable (EXC-Fe) holds relatively low content; while iron in carbonate (CARB-Fe) performs as traces. In addition to OM-Fe, ancient soil contains larger amount of iron in various forms than modern soil. WS-Fe, EXC-Fe, OX-Fe and OM-Fe content all present the trend of lift-to-drop in soil depth; while RES-Fe content aggrandizes in line with depth.(4) The iron content in buried ancient paddy soil, RES-Fe>OX-Fe> OM-Fe> WS-Fe. Among which, WS-Fe records the lowest while iron in carbonate bounded form and EX-Fe are with traces. Other than OX-Fe, buried ancient paddy soil contains larger amount than modern paddy soil. WS-Fe, OX-Fe and RES-Fe are highly involved in macro aggregates.(6) The infrared spectrum removing organic materials and free iron in buried ancient paddy soil reveals significantly wide absorption peak at the wave number of 650-350 cm-1 and demonstrates high absorption peak at the wave number of 350-100 cm-1. Calcium oxide spectrum becomes more distinctive after getting rid of organic materials. Although no significant difference exists between the characteristic peak of iron oxide and original soil, the peak decreases tremendously after removing free iron and photon absorbing intensity of other oxides adds. Meanwhile, the wave of infrared spectrum moves to low-frequency direction. From FD spectrum, it is concluded that photon absorbing intensity follows the trend:removing organic matters>removing free iron> untreated soil. |
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