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A Simple Textural Index for Assessing Chemical Weathering in Soils
Author(s) -
Torrent Jose,
Nettleton W. D.
Publication year - 1979
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1979.03615995004300020027x
Subject(s) - weathering , silt , udic moisture regime , soil water , soil science , geology , mineralogy , soil production function , parent material , particle size distribution , chemical composition , environmental chemistry , environmental science , particle size , geochemistry , chemistry , geomorphology , pedogenesis , loam , paleontology , organic chemistry
Chemical weathering affects the particle size distribution of soils, but little use has been made of this fact other than the inferences of increased chemical weathering generally made from increase in clay content. We postulated a simple model for assessing chemical weathering from particle size distribution. In the model, we assumed that a rind tends to peel‐off a mineral when the mineral is under attack by an advancing weathering front parallel to its surface. Using the model, we calculated theoretical particle size variations of some loessial soils. The calculations, as expected, showed that fine fractions (< 50 µm) are much more affected by chemical weathering than are coarse fractions (> 50 µm). We concluded from this that silt fractions may be used for assessing chemical weathering, but if they must be used for assessing uniformity of parent material, they should be used advisedly. We applied our model to 161 loessial soils of the Mississippi Valley, all having udic or aquic moisture regimes. We used the fine‐silt/total‐silt ratio trend for the upper part of the solum as a weathering index. The index correlates with mean annual temperature ( r = 0.70) which in humid regions is assumed to be the main factor involved in the chemical weathering of soils. Although our index is not universally applicable, it may help in comparing the weathering status of soils developed on similar parent materials.