Masters Theses

Date of Award

8-2003

Degree Type

Thesis

Degree Name

Master of Science

Major

Biosystems Engineering

Major Professor

Daniel Yoder

Abstract

This thesis evaluated multiple possible soil quality indicators in order to choose a small set for inclusion in a rapid soil quality measurement scheme. The scheme was developed to be used for examining soil quality changes caused by land use differences. A more rapid, albeit less detailed, assessment of soil quality will be valuable to researchers studying the effects of land use change where evaluation of multiple widely scattered sites is necessary in order to understand soil quality changes over a-wide range of treatments and site conditions. Research projects sponsored by the United States Department of Energy are examining the environmental changes that occur when agricultural land is converted to bioenergy production. A small number of these sites are heavily instrumented and sampled in order document environmental changes on site. This work would be greatly enhanced if many more locations and treatments could be sampled rapidly and cheaply. The goal of this thesis was to determine which measurements should be included in a rapid soil quality measurement scheme and to develop the scoring structure to accurately reflect changes in soil quality as measured by a larger suite of indicators. The experimental design utilized for indicator evaluation included four treatments: agricultural control, switchgrass, sweetgum trees with fescue cover, and sweetgum trees maintained with no cover crop. These treatments were replicated twice on severely degraded agricultural land near Huntsville, Alabama in 1995. The soil was sampled at planting and again in the fall of 2002 for each of the replicated treatments. The erosion rate was modeled based on the characteristics of the crops using the Revised Universal Soil Loss Equation (RUSLE). After careful consideration of each indicator, the measurement framework was fashioned with only two simple parameters in order to make it easy to use, and thus widely employable by researchers and land managers. Soil organic matter level and erosion rate were chosen due to their direct links to the health of the land, widespread use, ease of measurement or estimation, correlation to other important soil attributes, and sensitivity over the correct time frame. In order to make the soil quality measurement more site-specific, the organic matter and erosion indicators were scaled between one and zero based on the values measured for a ~50 year old forest (1) and an extremely eroded agricultural plot (0) nearby. Multiplying the erosion score by the organic matter score yielded the overall site health score. In this way, both indicators must be fairly high in order for the site to be deemed healthy. The treatments scored as follows: tilled agricultural (.05), sweetgum (.21), switchgrass (.15), and sweetgum with fescue cover (.34). The bioenergy treatments scored significantly higher than the tilled agricultural treatment, but the site will clearly take many more years to approach the health of a forest The other measured values of soil and plant characteristics yielded little information or were closely correlated to the chosen measurements and were thus not included in the scheme.

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