Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Agricultural and Biosystems Engineering

First Advisor

Stephen J. Marley


Four tillage systems were used to measure the effects of tillage-induced changes on bulk density, penetration resistance, soil temperature, moisture content, surface roughness, and aggregate mean weight diameter. The four systems included, five passes with a cultivator, one pass with rotavator, two passes with disk, and one pass each with moldboard and disk. Wheat emergence count and yields were evaluated. Field experiments were conducted in three different agro-ecological regions of Pakistan. Soil types varied from sandy clay loam to clay loam. Wheat (Triticum aestivum L.) was used at all sites. Prior to tillage, base line data for the above related physical properties were collected at three locations and at different depths in each plot. A complete randomized experimental design with three replications was used. Soil bulk density and penetration resistance were significantly affected by the tillage treatment at all three locations. A higher percentage changes in bulk density and in penetration resistance were observed in sandy clay loam than in clay loam soils. The lowest bulk density was observed for the rotavator treatment while the highest occurred in disk plots after tillage. Soil water content and soil temperature were affected by tillage. Surface roughness coefficients and water retention data indicated higher values for moldboard and lower for the rotavator. Mean weight diameters of soil aggregates were not significantly affected by the tillage treatments. Emergence was greatest in moldboard treatment followed by rotavator, then disk and cultivator treatments. Clay loam soil showed more yield differences due to tillage than did sandy clay loam soil. Higher yield in moldboard plowed plots corresponded to higher emergence, lowest penetration resistance and lowest bulk density, higher surface roughness coefficient and aggregate mean-weight-diameter. Minimum yield for cultivator and rotavator corresponded to lower emergence, higher penetration resistance and bulk density, and low surface roughness and lower aggregate mean-weight-diameter.



Digital Repository @ Iowa State University,

Copyright Owner

Syed Hasan Ali Rizvi



Proquest ID


File Format


File Size

212 pages