Abstract

Soil formation is influenced mainly by lithology, climate, organic matter, vegetation, topography, and time. Soil-forming processes have been well studied in temperate regions. However, there is little data on such processes in the tropics. In this work, we have studied the environmental magnetic properties of lateritic soils developed on gneiss and charnockite. We sampled surficial soils from different environmental settings (urban, agricultural, pristine, and gleyed) to determine the processes involved in their formation. A range of environmental magnetic parameters and inter-parametric ratios were investigated to determine the magnetic concentration, grain-size and mineralogy of the soil samples. Redness rating (RR) index was also calculated to estimate the reddening of tropical soils and to examine its relationship with magnetic properties. The pristine soils exhibit the highest average value for χ_lf and a higher value of χ_fd%, indicating a greater amount of ultra-fine magnetic minerals. The gleyed and agricultural soils are weakly magnetic, probably be due to waterlogging, and are characterized by a coarser magnetic grain size. A high proportion of “soft” ferrimagnetic minerals like magnetite and titanomagnetite is present in the samples (average S-ratio ~ 0.90). Hematite content is the highest in unburnt soils and the least in gleyed soils (unburnt > burnt > pristine > urban > agricultural > gleyed). The high concentration of hematite in these soils could be due to transformation of maghemite, resulting from low-temperature oxidation of magnetite. We documented a distinction between the magnetic properties of burnt and unburnt soil types as fire can significantly enhance the magnetic values of unburnt soils. The concentration of hematite (indicated by HIRM) and redness rating (RR) index are fairly well correlated for all the sample types with the exception of urban (r = 0.51; p = 0.11; n = 11) and unburnt soils (r = 0.60; p = 0.28; n = 5), which show a strong correlation. Therefore, RR index can be effectively used as an indicator of reddening of tropical soils due to pedogenesis. This study demonstrates that environmental magnetism can aid in differentiating the diverse environments of soils even though they developed on a similar rock type and under similar climatic conditions.

中文翻译：

---

印度西南部红土的环境磁特性

摘要

土壤的形成主要受岩性，气候，有机质，植被，地形和时间的影响。在温带地区已经对土壤形成过程进行了很好的研究。但是，在热带地区，有关此类过程的数据很少。在这项工作中，我们研究了在片麻岩和长方岩上发育的红土土壤的环境磁特性。我们对来自不同环境设置（城市，农业，原始和磨碎）的表层土壤进行了采样，以确定其形成过程。研究了一系列环境磁参数和参数间比率，以确定土壤样品的磁浓度，粒度和矿物学。还计算了发红等级（RR）指数，以估计热带土壤的发红并检查其与磁性能的关系。_lf和_χfd％的较高值，表明大量的超细磁性矿物。倾斜的土壤和农业土壤的磁性很弱，可能是由于涝渍造成的，其特征是具有较粗的磁性晶粒尺寸。样品中存在高比例的“软”亚铁磁性矿物，如磁铁矿和钛磁铁矿（平均S比率〜0.90）。赤铁矿含量在未燃烧的土壤中最高，而在灰土中最低（未燃烧>燃烧>原始>城市>农业>灰土）。这些土壤中赤铁矿的高浓度可能是由于磁铁矿的低温氧化导致磁赤铁矿的转变。我们记录了燃烧的土壤类型和未燃烧的土壤类型之间的磁性之间的区别，因为火可以显着提高未燃烧的土壤的磁性值。r = 0.51；p = 0.11；n = 11）和未燃烧的土壤（r = 0.60; p = 0.28; n = 5），具有很强的相关性。因此，RR指数可以有效地用作因成岩作用而使热带土壤变红的指标。这项研究表明，环境磁场可以帮助区分土壤的不同环境，即使它们在相似的岩石类型和相似的气候条件下发育。