This thesis examined the effect of continuous row-cropping on soil structure measured by bulk density and compaction ratings. Undisturbed core samples were collected from the selected sample sites to determine the bulk density. Compaction ratings were obtained by using a Proctor Penetrometer. A total of 192 soil samples were collected for this investigation. Comparisons of mean bulk densities, mean compaction ratings, and mean moisture percentages of the surface and Bt horizons of Blount and Pewamo soils in Delaware County, Indiana under three different field conditions: woods (untilled), field cultivated fields (continuous row-cropped), and plowed fields (continuous row-cropped) were made. This was done by calculating F-ratios and Bayesian Least Significant Difference ratios. Pearson's Product Moment Correlation' Coefficients were also calculated between selected parameters of the data. Conclusions drawn from these statistical analysis were discussed.

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Triaxial tests under high loading rates and different confining pressures simulate the multi-pass effect of a tractor wheel loading on the soil. A volume measuring technique was developed to be used in triaxial tests conducted under high loading rates. A sandy clay agricultural soil was tested under predetermined conditions using an INSTRON loading frame, a differential pressure transducer and an APPLE Il + microcomputer. A preliminary analysis indicated that the measuring technique that was developed, was capable of recording volume changes under high loading rates. Stress-density plots were created using the obtained data and a mathematical model was developed relating stress to density. Stress-strain data was used to evaluate the soil parameters under the Mohr-Coulomb failure criteria. Furthermore, the influence of the initial soil density on the soil behavior was evaluated and subsequently compared to the results of a similar study conducted under a different initial density. / Master of Science

A field study was conducted in the fall of 1982 to investigate the effect of vehicle type, traffic moisture level, and their interactions on soil compaction. During the study two procedures commonly used for soil bulk density determination were also compared. Treatments at the following levels were applied: i) Soil moisture: Two levels ii) Vehicle type: wheel and track type iii) Traffic intensity: 0, 1, 3, and 9 passes. Each treatment combination was replicated three times and these were installed in random order on 48, 6 x 30 m test plots. Soil samples were taken at three locations from each test plot for the determination of moisture level. Core samples were taken in and outside the rut at three locations along each track for bulk density determination. Bulk density data using a double probe nuclear densitometer were taken at one location along the track. Statistical analysis of the data indicated that, of the factors considered in the study, number of vehicle passes and interactions between moisture level and vehicle type and number of passes and vehicle type had a significant effect on the compaction of the top soil layer. The two methods for measuring soil density were compared using the paired student's t-test and an equation was developed relating the density values obtained by nuclear and gravimetric procedures. Comparison of the data from the two methods indicated that the nuclear densitometer underestimated the core bulk density. / Master of Science

Includes bibliographical references. The beneficial effects of tillage are often negated in Australian soils by poor aggregate structural stability. If irrigation or rain falls on exposed freshly tilled soil, crusting or harsetting often develops on drying. Rainfall intensity, kinetic energy, rate of wetting, antecedent water content and soil management history have been implicated in aggregate breakdown.

Includes bibliographical references. / xxiv, 177 p. : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The beneficial effects of tillage are often negated in Australian soils by poor aggregate structural stability. If irrigation or rain falls on exposed freshly tilled soil, crusting or hardsetting often develops on drying. Rainfall intensity, kinetic energy, rate of wetting, anticedent water contentand soil management history have been implicated in aggregate breakdown. / Thesis (Ph.D.)--University of Adelaide, Dept. of Soil Science, 1995