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Doctor of Philosophy




Humic acid carbon and fulvic acid carbon and inorganic phosphorus (IP) fractions and ratios were studied in selected loess-derived Mollisols and Alfisols of northeastern Iowa. Of the eleven profiles studied, ten formed in Wisconsin loess, one formed in alluvium. The soils formed under one of the following types of native vegetation: forest, forest-prairie transition, or prairie. Different slope and erosion phases of the prairie-derived (Tama, fine-silty, mixed, mesic Typic Argiudoll) and transition (Downs, fine-silty, mixed, mesic Mollic Hapludalf) soils were included in the study. Three of the Mollisols had impeded drainage;Within the stable members of biosequence, Tama-Downs-Fayette (fine-silty, mixed, mesic Typic Hapludalf), the secondary IP fractions, FeP, AlP, RSP (reductant-soluble P), and occluded P, in the 25 to 100 cm zone, were in the order forest-derived > transition > prairie-derived soils. The eroded soils had more CaP and active P than their stable analogues. Also, the eroded soils had less secondary P in the 25 to 100 cm zone than did the stable analogues. Active P includes NH(,4)ClP, AlP, FeP, and CaP;The soils with impeded drainage are Muscatine (fine-silty, mixed, mesic Aquic Hapludoll), Sawmill (fine-silty, mixed, mesic, Cumulic Haplaquoll), and Sperry (fine, montmorillonitic, mesic Typic Argialboll). These soils had more CaP, and less AlP and FeP than did the well-drained Tama soil. The Sperry profile, from an upland depression, had more RSP and occluded P than did the Tama profile;Alfisols had low H/F ratios than did the Mollisols. The buried profile (Sawmill) had the highest H/F ratios;Two profiles, Sawmill and Sperry, located at water collecting sites on the landscape, had relatively large accumulations of total phosphorus (TP). This implies lateral and vertical movement of phosphorus during soil genesis;Based on a correlation study, CaP contribution to the active P fraction decreased from prairie-derived (--->) transition (--->) forest-derived soils. Multiple linear regression models generally had high R('2) values;The IP fractions were useful for separating eroded from noneroded soils. High correlations between slope gradient and erosion phase imply that erosion and slope had similar effects on the variables investigated;The H/F ratios provided a good index for separation of the soils into Alfisols and Mollosols.



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Winston Edward Hobson



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385 pages