Date of Award:

5-1967

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Department name when degree awarded

Soil Chemistry

Committee Chair(s)

R. L. Smith

Committee

R. L. Smith

Abstract

Zinc deficiency, in many cases, is closely related to organic matter decomposition. DeRemer and Smith (1964) studied the effects of decomposing sugar beet tops on the reactions of Zn65 in a Portneuf soil. They found that with time the Zn65 associated with lime minerals, exchangeable, and water soluble fractions of the soil decreased, while that found with the organic and mineral fractions increased. This increase in the mineral fraction is of particular interest, since the majority of the Zn65 was found to be with this fraction after a period of time. They also showed that the increase in Zn65 associated with the sand-silt size fraction after a rough separation was greater than with the clay fraction. Smith, Henry, and Shoukry (1965) studied the Zn65 associated with the organic fraction as it changed with time. They found that the Zn65 associated with the fulvic acid increased rapidly during early incubation periods, but in the later incubation periods had decreased considerably and was found in the mineral fraction. Shoukry (1966), in a study of the effect of decomposing organic matter on the available Zn65 as determined with various reagents, found that after 12 weeks incubation a great portion of the Zn65 was found associated with the mineral fraction.

This reaction of the mineral fractions, especially the sands and silts, has not been explained, although several hypotheses do exist. It is possible that there is bonding of Zn by organic matter either directly to the sands or silts or to the edges of the crystal lattices of clay, causing these enlarged clays to separate out in silt-sized fractions. There also is the hypothesis of the Zn reacting directly with the sand and silt-sized fraction.

This experiment was established to investigate the reactions of the Zn with the mineral fraction of the soil. The major objectives were:

  1. To establish what size fractions are involved in the inactivation of Zn.
  2. To determine the effect of organic matter on the inactivation of Zn by various mineral fractions.
  3. To determine the effect of incubation of the soils on the inactivation of Zn65.

These objectives were investigated by using soils covering a wide range of Zn problems, from Zn deficient to border-line to non-Zn deficient. The soils were then treated with organic matter and Zn65 and subjected to different lengths of incubation. They were then mechanically separated into different fractions to determine the relation of these fractions to Zn inactivation.

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