Graduate Thesis Or Dissertation
 

Soils of the Oregon coastal fog belt in relation to the proposed "Andisol" order

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/6969z4167

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  • A study was conducted to evaluate the properties of soils in the fog belt area of the Oregon Coast Range. Soils in the study were chosen to include only those belonging to Andepts or to andic subgroups. Samples were collected from eleven sites that were formed mostly from colluvial deposits of basaltic rocks, sedimentary rocks, and alluvium derived from volcanic and sedimentary rocks. The soils studied were characterized chemically and physically, and the mineralogy of the very fine sand and clay size fractions was determined. The eleven soils were classified on the assumption that Andisol is added in the Soil Taxonomy as the 11th order. Based on the low degree of profile differentiation shown by profile morphology, it was concluded that all of the soils studied are in an early stage of development. The soil structure is mostly granular in the surface and fine subangular blocky in the subsoil. Field texture and laboratory analyses indicate low percentage clay compared to silt throughout the profiles. Surface layers are mostly dark colored. All the soils have low bulk density, high water holding capacity at high suction (15 bar), high CEC, high organic carbon, high pH in NaF, high variable charge, and high phosphorus retention -all of which indicate a high proportion of amorphous materials in the clay fraction. Based on the mineralogy of the very fine sand fraction and field site observations, it was concluded that basaltic and volcaniclastic rocks were the major sources of the parent materials that have weathered to produce a dominance of amorphous materials in the soils studied. Chloritic intergrade dominates the crystalline clay size components of all the soils with minor amounts of smectite, mica, gibbsite, chlorite, halloysite, and kaolinite. It was concluded that three out of the eleven soils studied, have chemical characteristics of spodic horizons based on the amount of extractable Fe and Al measured, These soils were classified as Troporthods. Eight of the eleven soils were provisionally classified as Andisols. Seven of the eight Andisols were placed in the subgroup Typic Haplotropands and one under the subgroup Typic Haploborand.
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