Masters Theses

Date of Award

6-1979

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

M. E. Springer

Committee Members

H. R. DeSelm, G. M. Lessman

Abstract

A transect study and a pedon sampling study were conducted in the Cumberland Mountains in Campbell County, Tennessee. Soil formation and forest productivity were considered in relation to soil-site-vegetation variables.

In the study area, the mean annual soil temperature was 14°C, and the mean annual precipitation was between 120 cm and 145 cm. Soil parent material was shale, siltstone and sandstone.

Soil morphological, site and vegetational data were collected on 141 sites on 28 randomly selected north-south transects.

A definite pattern of soils was evident. Fifty-seven percent were Hapludults, and 43% were Dystrochrepts. On south aspects, 76% of the soils were Hapludults; 24%, Dystrochrepts. On north aspects, 59% of the soils were Dystrochrepts; 41%, Hapludults.

Correlation analysis indicated soils from colluvium in lower and concave positions. An increase in slope gradient indicated less water-holding capacity. Depth to bedrock, thickness of argillic horizon and surface stoniness decreased with increasing elevation. A1 horizons were thicker and darker, and B horizon development was less on north aspects and high elevations.

Morphological differences between horizons were generally weak. Transition zones were thicker on north than on south aspects.

North aspects were more mesic than south aspects. Trees also segregated according to moisture conditions of the soil. Petros had more drought-resistant trees than Berks and Muskingum. Muskingum, Gilpin (tax) and Shelocta (tax) had less variety and more drought-resistant trees than Muskingum (tax), Gilpin and Shelocta. Depth to bedrock and coarse fragment content were major factors affecting distribution of taxa.

In a separate study, eight soils on north and south aspects at elevations ranging from 520 m to 920 m were selected for morphological, chemical, physical and mineralogical analysis.

Morphological differentiation between A and B horizons was stronger on south than on north aspects. A horizons were darker on north aspects. Redder hues were in B horizons on south aspects.

On north aspects, pH values were higher in upper horizons than in lower horizons. Values were more uniform throughout the solum on south than on north aspects.

Organic carbon was greatest in the soils on north aspects and at higher elevations than at other positions.

Soils on south aspects had argillic horizons; those on north aspects did not.

Coarse fragment content greatly reduced the soils' capacity to hold water. Available water also was reduced by coarse fragments and nearness of bedrock. Soils 3S and 4N contained <1/4 by volume coarse fragments and were <100 cm thick. They held less available water (8 to 9 cm) than thicker soils with fewer coarse fragments, such as soils 1N and 4S with 17 to 18 cm of available water.

Texture, structure and organic matter content were also important soil physical properties which determine available water. A clay content of <35% in soil 2S limited available water to 12 cm. Soil IN with a whole soil average of 2.5% organic carbon has 18 cm of available water.

Thus, available water as influenced by coarse fragment content and depth to bedrock among other soil physical properties was a prime factor determining differences in plant growth.

Site factors (aspect, slope gradient, slope shape, position, elevation and parent material) influenced the distribution of water and the amount of evapotranspiration. The amount of soil water recharge and rate of water loss were results of an interaction among soil-site factors. The soil's physical properties were responsible for interception and storage of this water which was then available for plant utilization.

In both the transect study and the pedon sampling study, difference in soil development was related chiefly to topography and elevation which caused differences in microenvironments on similar parent material. On north aspects and upper elevations, A1 horizons were thicker and darker than those of other positions, and on south aspects clay trans location and B horizon development were greater than on north aspects. Thus, both direction and intensity of soil formation were determined by differences in the microenvironments developed from varied topography and elevation.

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