Employees were going to remove an aeration pipe (18 inch in diameter and 10 feet long) that had potatoes on it with a 3/8" chain & a skid steer with forks. The chain was secured around the pipe and around both forks on the skid steer. After the pipe was free of the potatoes, the skid steer driver began to back up, while another employee guided the pipe. While backing up, one of the skid steer forks hit one of the bulkhead tubes (75-80#) that was sitting in its slot. The tube came out of its slot and fell roughly 7'8" striking the employee on the head. He fell backwards into the potato pile and suffered a head laceration.