Seedbed preparation is important for uniform crop emergence, plant growth and high yield under different soil and climatic conditions for any crop in drylands. A three-year study ( 2001 - 2003) was conducted to investigate the effects of three tillage systems on planting performance, aggregate properties, and crop yield of a loam soil ( typic Xerofluvent) with a rotation system ( sunflower ( Helianthus annuus L.)- barley ( Hordeum vulgare L.)- Hungarian vetch ( Vicia pannonica Crantz) and triticale). Tillage treatments were chisel ploughing, chisel ploughing and disc harrowing, and chisel ploughing and combine harrowing. Planting performance was determined only for sunflower. The emergence percentage of seeds sown, the percentage of plants which have an acceptable seedling interval, the percentage of gaps, and the percentage of double seedlings were used as the characteristics of planting performance. The highest percentage of gaps was in the chisel ploughing treatment, and the highest percentage of double seedlings was in the chisel ploughing and combine harrowing treatment. The percentage of gaps was reduced, and the percentage of double seedlings was increased by secondary tillage operations. Soil samples were taken from 0 - 20 cm depth at four different periods of the experiment. A wet-sieving method was used to determine aggregate size distribution and mean weight diameter as indices of soil aggregate stability. The percentage of water-stable aggregates for the three tillage systems was not significantly different in all size classes. Data showed significant differences among the effects of time on water-stable aggregates. The distribution of water-stable aggregates revealed that chisel ploughing and combine harrowing treatment caused an increase in the susceptibility of macroaggregates. While there was no difference among treatments for sunflower yield, barley and Hungarian vetch and triticale yields were lower in the chisel ploughing treatment. It is not recommended to dispense with secondary tillage operations in dry conditions, owing to the limited changes in aggregation among tillage systems and higher Hungarian vetch and triticale yields.