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Degree Name

Doctor of Philosophy




Noncrystalline materials have been studied mostly in the < 2 (mu)m fraction of highly weathered soils. Fifteen pedologically-young, loess-derived Iowa soils were used to study depth distributions of ammonium oxalate-extractable oxides of Al and Fe (OXAL and OXFE), KCl- and ammonium acetate-extractable Al (EXAL and EXTAL), and citrate-bicarbonate-dithionite-extractable Fe oxides (DITFE) in the < 2 mm fraction. Relationships between these Al and Fe parameters and other soil properties were studied by correlation and multiple regression analyses. Mineralogy of the < 2 (mu)m fraction was studied using x-ray diffraction analysis (XRD) and transmission electron microscopy (TEM);Ranges of EXAL and EXTAL vary from 0 to 8.5 and 6.12 meq/100 g, respectively; both show zones of accumulation in the Bt horizon. They decrease from soils formed under forest to those under prairie. Only in forest soils does EXAL increase with profile development. DITFE ranges from 0.4 to 2.5% and is less in poorer drained soils. Distributions of DITFE in the better drained soils show a maximum in the Bt horizon; they become more erratic as natural drainage becomes poorer. Amounts of OXAL and OXFE, noncrystalline oxides of Al and Fe, vary up to 0.46 and 0.93%, respectively. Weighted OXAL and OXFE means in the sola decrease with increasing stage of profile development under prairie vegetation, increase under forest vegetation, and show no change in the transition soils;Two alternative multiple regression models using combined data were developed for both OXAL and EXAL, one with PH (soil pH) terms and the other with HION (H('+) concentration) terms. Both final models for OXAL had high R('2) (0.91) and high prediction efficiencies in individual profiles. The final model of EXAL with HION had a higher R('2) than the one with PH (0.94 vs. 0.84);As shown by XRD, all soils have varying proportions of the following clay minerals: smectite, mica, kaolinite, vermiculite, hydroxy-interlayered materials, quartz, and leipidocrocite. Geothite and maghemite were identified by TEM. The only discrete noncrystalline material observed through TEM was amorphous silica; however, gel-like surface coatings of noncrystalline materials were observed on the crystalline clay particles of acid-dispersed clays.



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Andrew Manu



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417 pages