Date of Award
Doctor of Philosophy
Agricultural and Biosystems Engineering
Stephen J. Marley
Donald C. Erbach
The ridging effect of cultivator sweeps modifies soil microtopography affecting root environment and soil erosion potential. The effects of sweep rake angle (13.5°, 16° and 44°), speed (5, 7, and 9 km/hr), and depth (50 and 100 mm) on lateral soil movement into a ridge, ridge height and changes in surface elevation were measured. Dependent variables soil shift, ridge height and change in surface height were defined as measures of the change in soil microtopography;Techniques were developed and used to measure soil aggregate movement during sweep tillage. A comparison was made of actual soil flow to that predicted by the Goryachkin trihedral wedge model;Soil shift and ridge height were affected ([alpha] =.01) by both speed and tool geometry. Higher speeds moved more soil into the ridges. A modified sweep with rake angle of 44° produced greater ([alpha] =.01) soil shift and higher ridges than the commercial sweeps with rake angles of 13.5° and 16°. Comparing commercial sweeps, the 16° sweep produced a higher ridge ([alpha] =.05) and greater soil shift ([alpha] =.10) than did the 13.5° sweep;Change in surface height was significantly affected by tool depth ([alpha] =.01) and speed ([alpha] =.05) but not by tool geometry. Deeper operating depth created a higher soil surface. The relationship of change in surface height to speed was quadratic ([alpha] =.01);The lateral movement of soil away from the tool and into the ridge was more closely related to the vertical velocity component of soil on the tool than the lateral component. Surface soil velocities were generally unrelated to those on the tool surface. Speed and the tangent of tool rake angle had some influence on the change in microtopography;Observed soil flow paths varied with rake angle, but not with speed or depth, in agreement with the Goryachkin model. As rake angle increased the ratio of vertical to lateral soil movement increased. Predicted values were outside of a 99% confidence interval of observed mean values. Soil flow on the sweep did not vary appreciably (less than 5°) from a vertical plane parallel to the travel direction.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Harold Mark Hanna
Hanna, Harold Mark, "Changes in soil microtopography by tillage with a cultivator sweep " (1991). Retrospective Theses and Dissertations. 10037.