The objectives of this research were to evaluate reagents for use in a procedure to fractionate Cu in soils and to apply this methodology to soil incubated in the laboratory with added CuSO₄ or high-Cu swine manure. The evaluation procedure consisted of measuring desorption of Cu from a selection of clay minerals, organic materials, and hydrous oxides using reagents suggested in the literature. Adsorption of Cu by these materials was performed at pH 3.5 and 5.5 at two Cu concentrations, in the presence of 0.05 N CaCL₂. Despite the presence of excess electrolyte, 20-50% of the Cu adsorbed by montmorillonite was desorbed by N Ca(NO₃)₂, KCl, or Ca(ClO₄)₂. Less Cu was salt-exchangeable from humic acid and Fe oxides, and very little (<2%) from Mn oxides, reflecting the strength of bonding of Cu to these materials. Little effect of cation type on desorption was noted, but kinetic effects (up to 16 hours) and concentration effects (0.5 vs. 1 N) were noted. Specifically adsorbed (surface complexed) Cu was desorbed from these surfaces using 2.5% acetic acid and 0.1 N Pb(NO₃)₂, both reagents removing similar amounts (30-70%) of the adsorbed Cu, with Pb being slightly more efficient on some surfaces. Release of Cu from organics after Pb extraction was evaluated using 0.1 M K₄P₂O₇, 5% acetyl acetone, and 5% NaOCl. The former reagent was shown to be most effective, but also to have a solubilizing effect on Mn oxides. In a sequential scheme, therefore, removal of Mn oxideoccluded Cu by 0.1 M NH₂OH·HCl(pH 2) was designed to precede K₄P₂O₇ extraction. Dissolution of poorly crystalline Fe oxides by 0.275 M oxalate (pH 3.2, in darkness) was found to be selective and efficient, while this reagent under uV irradiation solubilized most crystalline Fe oxides, except hematite, more effectively than dithionite. The final sequential procedure consisted of H₂O extraction, followed by N Ca(NO₃)₂, 0.1 N Pb(NO₃)₂ 2.5% acetic acid (to dissolve Cu precipitates and residual complexed Cu), 0.1 M NH₂OH·HCl, 0.1 M K₄P₂O₇, 0.257 M oxalate (pH 3.2, darkness), oxalate under uV light (85C, 3 hours), and residual HF digestion.
This procedure was applied to three Virginia soils treated with high rates (45 dry t/a) of high-Cu swine manure, or equivalent rates of CuSO₄ (50 ppm, soil basis). Fractionation was performed after 1, 4, 12, and 29 days of incubation at 30C. Compared to untreated soils, Cu-manure increased soluble Cu over the whole incubation period, while CuSO₄ treatment increased exchangeable Cu initially, but this decreased to near control levels by day 12. Nearly 80% of the added Cu from both sources was Pb- or acetic acid-extractable, the CuSO₄ being more easily displaced by Pb and the manure Cu by the acid. The organic Cu (K₄P₂O₇-extractable) increased slightly with Cu-manure additions, and there were smaller gains in the Fe and Mn oxide fractions. Fractionation of the high-Cu manure suggested nearly all the Cu was in an organic form, possibly low molecular weight organics that associated with soil surfaces upon addition to soil. Although manure treatment resulted in increased soil organic matter levels, an initial Eh decrease (to near 0 mv), and a rise in pH (to 7-8), there was little difference in the distribution of Cu between the fractions due to Cu source or between the three soils. Specific adsorption was the major retention mechanism, although the reversion of Cu to organic and oxide forms was hypothesized over long time spans. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/101307 |
| Date | January 1981 |
| Creators | Miller, William Paul |
| Contributors | Agronomy |
| Publisher | Virginia Polytechnic Institute and State University |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | viii, 160 pages, 3 unnumbered leaves, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 07510810 |
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