In onion (Allium cepa L.) harvesting, several steps, such as leaf topping, bulb-soil separation, and bulb collection, are performed. One of the methods for separating onion bulbs from the soil during harvest is the use of a rod-type onion digger. In this machine, the rotation and translational movement of a rod beneath the root zone of the onions causes the detachment of the bulbs and their extraction from the soil. The required energy for separating onions from the soil is primarily consumed in two main parts: the draft force for moving the unit components through the soil, and the rotational energy of the rod beneath the onion roots. Various factors, such as soil structure and moisture, as well as design and operational parameters of the digger, such as forward speed and working depth, affect the required energy. In this study, the effect of forward speed and working depth of a rod-type onion digger on the energy required for onion separation from soil was investigated. For this purpose, a split-plot experimental design based on a randomized complete block design with three replications was used. The working depth of the harvester at two levels (5–7 cm and 10–12 cm) was considered as the main plot, and forward speed at three levels (0.35, 0.4, and 0.5 m/s) as the subplot. In each experimental treatment, draft force and drawbar power, as well as torque and rotational power required for the digger, were measured. According to the results, the average draft force required to move the digger through soil with a working depth of 7–12 cm ranged between 4865 and 6400 N, and the required drawbar power ranged from 1857.5 to 3125.5 W (24.33–31.25 kJ/ha) per meter of working width. Moreover, the measured torque for rod rotation in the soil ranged between 25.2 and 35.1 N m, and the required rotational power ranged from 1079 to 1814.5 W (13.88–18.14 kJ/ha)/m of working width. Based on these calculations, the total energy required for onion bulb separation per meter of onion digging width was estimated to be between 38.22 and 49.40 kJ/ha.
