Graduate Thesis Or Dissertation
 

A model for determining soil contrast and its application to five different soil orders

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  • A well-defined, quantitative model for determining soil contrast was developed to improve soil survey interpretations concerning the effects of mixtures of different kinds of soils on agricultural land use. The model was evaluated by determining the levels and reasons for soil contrast on mapped soil areas representing 5 different landscapes, each dominated by a different soil order. Several preliminary models are discussed. The final model is based on twelve soil properties including slope, drainage, depth of rooting, texture and pH. For each property, the range of possible values was divided into a small number of classes. By comparing classes, five levels of contrast (Very Similar, Similar, Somewhat Contrasting, Contrasting, Very Contrasting) were established within each property. These same five terms, plus an additional Exceedingly Contrasting class, were used to characterize the overall degree of contrast between any two soils. Overall contrast was determined by first comparing the property values of a pair of soils and determining the degree of contrast for each property. Then the overall contrast was set equal to either the contrast level for the most contrasting property or properties, or to the next higher contrast level if several properties varied between the two soils. Distributions of contrast levels within soil landscapes show that areas of Inceptisols, Ultisols, Alfisols and Mollisols are characterized by a high percentage of similar soils. The Aridisol landscape sampled had the highest percentage of exceedingly contrasting soils. The Alfisols and Mollisols sampled have the highest percentage of somewhat contrasting and very contrasting soils, respectively. Reasons for soil contrast were determined both by identifying those few properties that actually dictated the contrast level and by calculating a weighted average contribution of each of the 12 soil properties. In general, lower levels of contrast were controlled by one or two properties. At higher levels of contrast, more properties varied, and no property had as dominant an effect. Slope was the major factor controlling the contrast of similar soils. Drainage, pH, texture, and depth of rooting differences, all of which reflected differences in parent materials, were most often expressed at somewhat contrasting or contrasting levels. The most common reason for very contrasting soils was flooding, and that occurred where an alluvial soil was adjacent to an upland soil.
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  • File scanned at 300 ppi (Monochrome) using Capture Perfect 3.0.82 on a Canon DR-9080C in PDF format. CVista PdfCompressor 4.0 was used for pdf compression and textual OCR.
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file details VillamayorFaustinoPaysan1987.pdf 2017-08-04 Público Baixar