Inaug.-Diss.--Bonn, 2000. / Includes bibliographical references (p. [119]-124).

Call number: LD2668 .T4 1938 R62

Call number: LD2668 .T4 1984 S22 / Master of Science

The data of 14 soils were used to compute the ion activity product (IAP), the ratio of the ion activity product and to the solubility product (Ksp) of the pure minerals (IAP/Ksp) and to estimate the solid activity coefficients (SAC) of the soil components. The value of IAP and SAC of AlPO4 differs from soil to soil and increases with increasing P added to soil in acid soils and for calcium phosphate in basic soils. Magnesium apparently did not cause P adsorption or precipitation in the soils studied. The SAC of aluminum phosphate ranged from 10 to 10000 in acid soils. The mole fraction of the total phosphate in soil seemed to be a more satisfactory basis for calculating the concentration of the solid phase than was measurements of the available phosphate.

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Prevention of groundwater contamination by agricultural chemicals requires an understanding of the complex processes that control pesticide movement below the soil surface. Through this understanding it is possible to try to predict which areas may be most vulnerable to contamination. The many models that have been developed to characterize pesticide movement vary widely in their conceptual approach and degree of complexity. A soil properties model was developed in this thesis to determine the relative overall pesticide movement potential in Oregon agricultural soils. Its focus is ease of use in both acquisition of input values and running of the model. The model is based on soil properties important in controlling pesticide movement. It is a rating system model that uses scoring of factors and matrices to weigh the soil values. It is organized into two processes: leaching and sorption. The leaching potential is based on soil permeability and drainage class. The sorption potential is based on organic matter content and texture of the soil surface horizon(s). The interaction of these two processes results in the overall pesticide movement potential. / Graduation date: 1991

Cadmium (Cd) from the soil can accumulate in our bodies via the consumption of our crops and cause serious health problems. While it has been documented that long-term cultivation affects physical and chemical properties of soil, little is known about its effect on the phytoavailability, solid-phase speciation, and profile distribution of soil Cd. The objectives for this study were to determine the effect of long-term cultivation on: (1) a cadmium availability index (CAI) that reflects phytoavailable Cd for durum wheat, and related soil properties, (2) the solid-phase species of soil Cd and relationships between the CAI and the solid-phase species of soil Cd and related solid-phase soil component properties, and (3) the profile distribution of total soil Cd in the past, and the profile distribution of total soil Cd over the next 100 years. One Orthic Chemozemic soil profile was investigated from a virgin and an adjacent long-term cultivated field at eight sites in the Brown, Dark Brown, and Black soil zonesof Saskatchewan, Canada. Long-term cultivation significantly decreased the CAI. A decrease in total Cd, total Zn, and CEC, and an increase in aromaticity of the soil organic matter and soil pH all contributed to the decrease in the CAI. Both the virgin and cultivated soils had the same solid-phase Cd species with the same order of relative abundance: metal-organic complex-bound > easily reducible metal oxide-bound > H2O2 extractable organic-bound > crystalline metal oxide-bound > exchangeable. However, metal-organic complex-bound Cd and H2O2 extractable organic-bound Cd decreased significantly with long-term cultivation. In the virgin soils two solid-phase Cd species correlated significantly with the CAI: exchangeable Cd (r = 0.93) and easily reducible metal oxide-bound Cd (r = -0.88). In the cultivated soils three solid-phase Cd species correlated significantly with the CAI: exchangeable Cd (r = 0.95), metal-organic complex-bound Cd (r = 0.71), and crystalline metal oxide-bound Cd (r = 0.86). For both the virgin and cultivated soils, the concentration of A horizon Cd > C horizon Cd > B horizon Cd. In the past, A horizon Cd concentration decreased significantly with long-term cultivation. However, it is estimated that in 100 years, with the use of phosphate fertilizer made from Idaho ore, the total A horizon Cd content in these soils could be 3.5 times higher and reach a concentration of 1.18 mg Cd kg-1 soil which is in the critical region where the phytoavailability of soil Cd could increase dramatically. The present study has advanced the frontiers of knowledge on the effect of long-term cultivation on the Cd content and distribution in the soil profile, its phytoavailability index, solid-phase species, and the soil properties related to its phytoavailability. Extending research such as this to other major agricultural soil types and farming practices will assist in the development of innovative management strategies to curtail Cd contamination of the terrestrial food chain.

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 148-163).

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No description available.