A method is provided. In this method, a first tray positioned at a first end of a trough assembly at a selected tier is engaged. The first tray is then lifted and removed. A second tray is then engaged and moved vertically to the selected tiers. It is placed in the trough assembly at a second end. Other trays—which are positioned within the trough assembly between the first and second ends of the selected tier—are moved toward the first end of the trough assembly.