Date of Award:

5-1956

Document Type:

Thesis

Degree Name:

Doctor of Philosophy (PhD)

Department:

Plants, Soils, and Climate

Department name when degree awarded

Soil Chemistry

Committee Chair(s)

D. W. Thorne

Committee

D. W. Thorne

Committee

Norman Bauer

Abstract

Zinc is one of the essential elements required for the normal growth of plants. The total amount of zinc commonly occurring in soils is usually many times greater than that necessary to supply the needs of actively growing plants. The ability of the soil to "fix" zinc in form unavailable for plant use, however, has made the zinc deficiency disease an important plant nutrition problem in the major fruit and nut growing regions of the West. Fixation mechanisms which have been postulated as contributing to zinc deficiency include organic complexes, precipitation of insoluble inorganic salts, and strong zinc-clay intersections. It may be possible that in certain soils naturally occurring soil minerals, other than the clay minerals, may also exert an influence on the capacity of the soil to retain zinc.

The accumulation of lime minerals is a distinguishing profile characteristic of soils in arid and semi-arid regions. These minerals include: calcite (CaCO3), dolomite (CaMg(CO3)2), and magnesite (MgCO3). Despite the widespread occurrence of these minerals in the soil system, relatively few data exist which specifically isolate the interaction between cations in solution and the solid phase of the above-named lime minerals.

It is generally believed that the adsorptive capacity of a mineral soil is manifested primarily in the clay fraction. However, it may be possible that some modification of this concept may have to be introduced when considering relatively unweathered soil systems.

All crystalline phases of matter in the soil capable of existing in a finely divided state, when dispersed in solution, inherently possess an adsorption potential because of the unsaturated forces which exist at all interfaces. Therefore, perhaps calcium carbonate and the other slightly soluble lime minerals can be regarded as potential adsorption sites for certain ions. The contribution that these minerals make to the adsorptive capacity of the soil for a given ion will depend not only on the magnitude of the attractive force that exists for the given ion at the interface of the crystalline phase, but also on the percentage of the total specific surface area of the soil that is contributed by the mineral phase in question.

Although many factors obviously affect the availability of zinc in calcareous soils, the prominence of lime minerals in many western soils is indicative of the importance of the zinc-lime mineral relationship in the clarification of soil factors which affect the availability of zinc.

The objectives of the study reported here are: (1) to obtain a quantitative measure of zinc adsorption on calcite, dolomite, and magnesite, and (2) to develop a theoretical approach to the surface phenomenon by which it may be possible to thermodynamically define the adsorption of zinc in a lime mineral system.

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