Thesis (M.S.)--University of Nevada, Reno, 2008. / "December 2008." Includes bibliographical references (leaves 109-112). Library also has microfilm. Ann Arbor, Mich. : ProQuest Information and Learning Company, [2009]. 1 microfilm reel ; 35 mm. Online version available on the World Wide Web. Library also has electronic version on CD-ROM

Thesis (M. Sc.)--University of Hong Kong, 2002. / Also available in print.

Thesis (M.S.)--Oregon State University, 1991. / Typescript (photocopy). Includes bibliographical references (leaves 69-72). Also available on the World Wide Web.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 2001. / "April 6, 2001." UMI order no. 3030350 Includes bibliographical references.

Thesis (M. Sc.)--University of Hong Kong, 2002.

No description available.

Crop production systems which utilize the biomass produced by rye (<i>Secale cereale</i> ) to suppress weed growth and conserve soil moisture have been developed at Virginia Tech. The success of alternative, reduced-input crop production systems has encouraged research into the potential for breaking the traffic-tillage cycle associated with conventional tillage crop production systems. The fragile residues encountered in agricultural crop production, whether incorporated into the soil or distributed on the soil surface, provide minimal protection against compaction by wheeled vehicles. The potential of an intact cover crop to reduce machine-induced effects on soil properties that affect primary crop growth was the subject of this study. A randomized complete block experiment was conducted at the Whitethorne Farm in Montgomery County, Virginia. One set of plots was arranged on a terrace adjacent to the New River in a fine, mixed, mesic, Aquic Argiudolls. Another set of plots was arranged on an upland site, a river terrace tread, in a fine-loamy, mixed, mesic, Typic Hapludults. Three rye cover crop treatments were examined. In one, a live cover crop was completely undisturbed prior to tracking by a wheel-type tractor. In another, the cover crop was chemically desiccated, and in the third treatment, all above-ground biomass was removed from plots prior to machine traffic. The treatments permitted investigation of the effects of crop condition on machine-induced soil compaction and the contribution of root reinforcement to the alteration of soil response to machine traffic. A fall-tilled fallow treatment served as an experimental control. Three levels of traffic were investigated: one pass, three passes, and five passes. Undisturbed soil core samples were analyzed to determine machine-induced effects on dry bulk density, pore size distribution, and saturated hydraulic conductivity. The treatments affected soil response to machine traffic. The cover crop treatments altered the soil-plant microenvironment, affecting soil parameters that influence compactibility. Soil compaction was attenuated by the reinforcing effect of a network of undisturbed roots within the soil. There was no convincing evidence that above-ground biomass contributed directly to the reduction of machine-induced compaction effects. Soil response to machine traffic was limited to the uppermost 15 cm of the soil profile. / Ph. D.

M.S.

The main purpose behind this thesis was to study the variations of strength in a soil after it had been stabilized with various percentages of lime, cement, and combinations of the two. In both cases where the additives were added separately to the soil, the percentages used were 5 and 10 per cent by dry weight of soil. In the additive combination study, lime-cement percentage additions were 2-3, 3-2, 4-6, and 6-4 by dry weight of soil. The first two percentages, when added together, amount to 5 per cent stabilizing agent, while the latter two total 10 per cent. Since these two totals were the same as those used in the separate lime and cement studies, an analysis of strength changes when lime, cement, and lime-cement combinations were added to the soil could be made. Strength studies which were made consisted of unconfined compression immediately after compaction and after a four-day curing period in a 100 per cent humidity curing room. Atterberg limit tests were also run at the various percentages of additive. The laboratory test results indicate: 1. For cured specimens containing a stabilizing agent, the greatest four-day strengths will occur at or above OMC, in most cases. This may not always be true in the case of cement, since moisture condition is not as significant in cement stabilization as it is in other types. 2. Control of moisture at or near OMC during field compaction appears to be much more important in lime stabilization than in cement stabilization if maximum strengths are to develop. This statement is supported by a statistical analysis which was performed on the strength data. 3. The variation of' the lime-cement percentage trom 6-4 to 4-6 has no effect on four-day cured strengths. / M.S.

Master of Science