Knowing the draft force is one of the primary necessities for designing, manufacturing and operating of agricultural implements. In this research, the effect of the tractor engine rotation speed (at three levels: 1000, 1500 and 2000 rpm) and gear ratio (at three levels: 1, 2 and 3 high) and implement working depth (at three levels: 4, 7 and 12 cm) on draft force of a drill seeder was investigated using a hydraulic dynamometer in a clay loam soil, Karaj, Alborz. Each treatment was considered in three replications, totally 27×3 experiments. The obtained data were analyzed as factorial test based on randomized complete design. The results showed that the effects of engine rotation speed, gear ratio, working depth and their interactions effects on draft were significant at 1 % probability level. The draft force was increased by increasing of engine rotation speed, gear ratio and working depth. The minimum draft was obtained in working depth of 4 cm, 1st high gear and engine speed of 1000 rpm and the maximum draft was in working depth of 12 cm, 3rd high gear and engine rotation speed of 2000 rpm with amount of 10.69 and 14.22 kN, respectively.
