Masters Theses

Date of Award

6-1969

Degree Type

Thesis

Degree Name

Master of Science

Major

Agronomy

Major Professor

M. E. Springer

Committee Members

H. C. Smith, H. R. DeSelm

Abstract

In the western Kenai Peninsula, Alaska, the well drained Cohoe and Island soils have formed in a mixture of volcanic ash and loess. The Cohoe soils have some properties of Spodosols and support a climax spruce forest. The Island soils are classified as Inceptisols and occupy broad, shallow grass-covered depressions that occur as openings within areas of the forested Cohoe soils, Field evidence indicates that in western Alaska the forest is advancing at the expense of the grasslands. In soils high in volcanic ash or other pyroclastic materials that yield high amounts of amorphous materials, it is sometimes difficult to distinguish between a spodic and a cambic horizon by the kinds of measurements commonly made in the laboratory. Several lines of evidence indicate that Andepts are converted to Spodosols in a relatively short time following their occupation by spruce forest in western Alaska. The main objective of this study was to apply some of the physical and chemical studies which are commonly used to distinguish between spodic and cambic horizons high in amorphous materials. A second objective was to relate the soil forming factor of vegetation to the morphology of these soils. Two transects extending from the grass-covered Island soils to the forested Cohoe soils were chosen near Ninilchik on the southwestern. Kenai Peninsula. Samples from horizons were taken from representative pedons of an Island, a Cohoe, and a transitional soil on the forest grass border. Some of the chemical studies included: (1) cation exchange capacity, (2) exchangeable bases, (3) percent organic carbon, (4) percent nitrogen, (5) extractable acidity, (6) percent free iron, and (7) pH values determined in water paste, N KCl paste, and .0.1M CaCl2. In addition, pH values were determined in 1N NaF. X-ray, DTA, bulk density, and pyrophosphate dithionite extractable C, Fe, and A1 studies were made on the horizons of the sola. Percentage water retention at 15-bars was determined on air-dry, field-moist, and oven-dry samples. Particle size distribution was determined by the standard method of dispersion using hexametaphosphate preceding overnight shaking. In addition, results were compared on air-dry and field-moist samples. On selected horizons, ultrasonic sound was employed as an additional dispersant. The difficulty of wetting and differences in percentage water retention at 15-bars on field-moist and air-dry samples showed that these soils dry irreversibly. Particle size distribution suggested incomplete dispersion by all methods used. X-ray, DTA, and NaF pH values indicated a high content of amorphous material, but not a high content of allophane. The organic fraction was almost as important a part of the active fraction as was the clay in the chemical properties that were measured. Pyrophosphate dithionite extractable C, Fe, and A1 were similar at comparable depths in the three soils studied. The forested Cohoe and Transitional soils have thin albic hori-zons over reddish B horizons that have some properties of spodic horizons; the grass-covered Island soils have thick, dark umbric epipedons. The laboratory studies, however, revealed that the difference in measured properties were small.

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