A knife assembly mountable to a frame of a seeder comprises a knife shank having a proximal end and a distal end, the proximal end of the knife shank adapted to be directly or indirectly attached to the frame; a knife blade removably attached at or near the distal end of the knife shank; and a tube holder having a groove along a portion of its length, the groove designed to slidably receive a corresponding ridge on a flexible drop tube so that when a portion of the bottom of the flexible drop tube is worn, the flexible drop tube can be pulled from the bottom to slide down the groove and the worn portion can be cut off, the tube holder being attached at or near the distal end of the knife shank behind the knife blade so that both the knife blade and the flexible drop tube can be removed individually.