Call number: LD2668 .T4 1986 B62 / Master of Science / Biological and Agricultural Engineering

Includes bibliographical references (leaves 11-1-11-26). / xv, 222 leaves : ill. (some col.) : 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--Adelaide University, Dept. of Agronomy and Farming Systems, 2001

The objective of this research was to further understand the behavior of the soil under the action of a tillage tool, with the purpose of finding a relation between the tool geometry and the resultant soil seed bed. Thus the problem consisted of understanding the mechanics of producing soil break up and to find a logical method of analyzing it. / The problem was solved using fundamental principles of soil mechanics and force equilibrium analyzis. As a result, a mathematical model was developed which describes three failure zones within the cut soil volume. The model can be programmed into a computer to generate maps of normal and shear stresses to visualize the three failure zones. / The failure zones are the shear failure zone, the tensile fracturing zone and the no failure zone. The tensile fracturing zone is delimited by the tensile stress reaching the tensile strength of the soil at the given soil moisture content and soil density. The tensile strength of the soil was measured using an apparatus and method designed in this research. / The mathematical model gives an explanation of the mechanics of crumbling and the shape of the failed volume, but it does not give information concerning soil aggregate quality and arrangement within the soil furrow. Then, a method of analyzing the formed aggregates was developed which considers some soil physical properties of aggregates. / The study concluded that the smaller tool width and the smaller tool rake angle, among the ones used in this research, produced the most efficient geometry in producing the largest amount of soil break up, the most uniform aggregate formation and the most stable aggregate arrangement. The same tool geometry requires less energy per unit volume of soil disturbed. The best performance is produced at the lowest soil water content among those tested.

A field tillage tool carrier was constructed using a tractor trailer, hydraulic cylinder and steel construction material. Tillage tool blades of varying lengths, widths and angles of attack were fabricated from steel and were used in the study of the effect of tool rake angle, tool width and depth of operation on soil strength properties, draft, draft efficiency, volume of soil manipulated, degree of soil loosening and penetration resistance. / The results showed that the draft increased with tool rake angle and width. Operating at a depth of 150 mm and 100 mm depth did not make any significant difference on the draft requirement. Low angles of attack were observed to have a greater potential to loosen the soil, and the loosening increased to a depth of 150 mm then decreased. The draft efficiency was affected by the angle of attack as well as the depth of operation. The cross sectional area of the furrow and hence the volume of soil manipulated was seen to depend on the width of the tool and the operating depth. / Slender tools and high rake angles were found to loosen the soil better than wide ones. No distinct trend existed between depth to width aspect ratio and draft requirement. No variation was observed between draft efficiency and d/w ratio. Penetration resistance increased with depth of operation as well as distance from the furrow centre after tillage. Some areas of residual high strength were sometimes left within the sphere of influence of the tools. Some tools dealt with these omissions better than others.

The physical state of the seedbed is of importance to the plant environment as it influences some important processes in the soil such as seedling emergence, water and solute transport, and ease of root penetration. This is affected to a large extent by tillage process, the tillage implement type and the geometry of the implement used. / A field experiment was carried out on a clay soil to determine the effect of the geometry of bladed tillage implements on some soil physical properties after tillage. The soil properties evaluated were bulk density, mean clod size distribution and total pore space after tillage and the extent of loosening achieved. / Implement parameters considered were blade width, rake angle and depth of operation of the implement. Two blade widths of 75 and 150 mm were evaluated in combination with three rake angles of 30, 60 and 90 degrees. Each tillage implement was drawn through the soil at four operating depths of 100, 150, 200 and 250 mm. / Larger rake angles were observed to result in larger mean aggregate sizes and greater bulk density reductions when compared to smaller rake angles. Greater reduction in bulk density was observed with the wider of the two blade widths evaluated. Mean clod size after tillage was also observed to be large for the wider of the two widths evaluated. Irrespective of width and rake angle, greater operating depths resulted in larger mean clod sizes and greater reductions in bulk density as compared to shallower operating depths. Fractal analysis showed the extent of fragmentation to be greater at shallower operating depths, hence the small mean clod sizes obtained.

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Call number: LD2668 .T4 1986 R43 / Master of Science / Biological and Agricultural Engineering