Date of Award:

5-1957

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

Committee

H. H. Wiebe

Abstract

Throughout the years lime-induced chlorosis has contributed to untold economic losses. Although this disease has challenged the technical ingenuity of outstanding plant and soil scientists, the exact cause has never been determined; consequently, no preventative measures or permanent cures can, as yet, be recommended. This physiological malady, unchecked, continues its rampage in regions where the disease is prevalent.

The problem is of wide significance because calcareous soils are distributed throughout the world. It is of primary concern to us because the majority of the land of western United States is of this type. An estimated 500,000 acres of crops growing on lime soils are subject to moderate and severe chlorosis in the western states alone. This disease is characterized by an interveinal yellowing of the leaves at the meristematic region combined with reduction of growth and vigor of the plant as a whole. Mild chlorosis induces marked reductions in crop yields, and severe cases are associated with die-back of terminal growth and ultimate death of the plant. Since a great variety of plant species are susceptible to this disease, plant growers of all types have been continually faced with this physiological problem. Great monetary losses result from damage to fruit trees and also to landscape and ornamental plants because of their high aesthetic value.

This form of iron deficiency is unique in that examinations reveal, with exceptions, that the soil and plants contain ample quantities of iron for optimum plant growth. The iron appears to be inactivated within the plant so as to impair proper functioning. An added peculiarity is the fact that chlorotic conditions are not stable as they vary from year to year and even from day to day with changing conditions in climate and soil. The problem has many complexities such as chlorotic and non-chlorotic plants of the same variety growing side by side in the field.

Although no single factor has given an adequate explanation for this physiological disease, many factors have been associated with its cause. Instances have been cited in the literature to the effect that calcareous soil conditions characterized by fine texture, high moisture content, poor aeration, and cool temperature intensify the development of chlorosis in plants. (Thorne et.al., 1950). The above conditions contribute to increased CO2 solubility with a consequent rise in pH and HCO-3 concentration of the soil solution. This increase in HCO-3 concentration is even more marked in the immediate region of plant roots where the CO2 gradient is the highest. Observations have indicated that the HCO-3 is the predominant anion on the external surface of the root, and as such, would be inhibitory to outward diffusion of CO2. Higher levels of HCO-3 maintained at the root surface are equivalent to higher levels of CO2 pressure at an elevated pH. Overstreet et.al. (1942) pointed out that respiratory activity is essential for the process of salt accumulation by roots; hence, it is conceivable that the respiration and other processes would be disrupted if the end-product of respiration is intensified in the absorbing cells. Miller (1954) found marked inhibition of respiration of excised bean roots in the presence of HCO-3.

The foregoing observations suggest that the build-up of toxic concentration of HCO-3 in the immediate vicinity of the roots intensify the onset of lime-induced chlorosis. It is the objective of this research to shed further light on the role HCO-3 and pH in lime-induced chlorosis.

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