Mineral magnetic properties of Chinese paddy soils and its pedogenic implications

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• 作者：Sheng-Gao Lu ; ^{lusg@zju.edu.cn} ; Lei Zhu ; Jin-Yan Yu
• 关键词：Magnetic susceptibility ; Paddy soil ; Waterlogging ; Pedogenesis ; Magnetic minerals
• 刊名：Catena
• 出版年：2012
• 期刊代码：11_03418162
• 类别：ear
• 出版时间：June, 2012
• 卷：93
• 期：Complete
• 页码：9-17
• 文件大小：1198 K

摘要

Magnetic susceptibility (MS) of paddy soils (Hydragric Anthrosols) and their corresponding dryland soils formed on the same parent materials in Zhejiang Province of Eastern China were measured in order to understand better magnetic profile discrimination and pedogenic magnetic minerals in paddy soils. Magnetic measurements showed that the MS values of paddy soils were much lower than those of dryland soils formed on the same parent materials. The higher the MS value of the original dryland soil is, the more remarkable the decrease in the MS value is when the soil is put under rice cultivation. Gleyed paddy soils exhibited very low MS value (< 20 脳 10^鈭?#xA0;8 m³kg^鈭?#xA0;1) and frequency-dependent susceptibility (< 3%), as well as greater enhancement of MS on heating. Waterlogging incubation experiment indicated that the MS loss of soil mainly occurred in day 15 to day 75 after water saturation. During the reduction period of 180 days, the overall MS losses of soils developed on Quaternary red clay and alluvial deposit were 78%and 80%, respectively. The MS values of various particle size fractions in paddy soils were also much lower than those of dryland soils formed on the same parent materials. The largest loss in MS value occurred in the clay fraction of paddy soil, which suggested that magnetic grains in clay fraction were readily dissolved. Thermomagnetic (魏-T) analysis indicated that paddy soils had very different and complex behavior of MS with increasing temperature, which can be explained by the predominance of ferric oxide in a poorly crystalline phase. Thermal behavior of magnetic susceptibility suggested that ferrihydrite was present in all profiles of paddy soils. The illuvial horizon of paddy soils was enriched with crystalline nano-scale iron oxide phase (mainly goethite, hematite, and maghemite/magnetite). The oxidation and reduction cycle in paddy soils could lead to the formation of nanocrystalline iron oxide, which provided a new pathway to explain the formation of pedogenic magnetic minerals. Paddy soils showed an obvious magnetic profile differentiation due to the difference in soil pedo-hydrological regimes. Three distribution patterns of MS profiles could be identified in paddy soils. The differentiation of MS in paddy soils can be used to describe soil profile characterization, identify diagnostic horizon, and interpret soil hydrological regimes. These findings provided new tool for profile description, type identification, hydrological regime diagnosis of paddy soils. Our results also help understand magnetic dynamic of soils caused by waterlogging process.