The present disc opener assembly for a seed planter is for a single disc opener arrangement and is embodied in several embodiments. FIGS. 1 and 1a illustrate two embodiments of the present disc opener assembly the specifics of each will be described below. Referring now to FIGS. 1, 1a and 2, there is illustrated a disc opener assembly (10) mounted on a tool bar (7) connected to a work vehicle (5) for opening a seed trench (8) in the ground upon which the vehicle (5) moves. A main arm (12) is attached to the tool bar (7) with a disc (14) mounted for rotation on the main arm (12). A depth adjustment mechanism (40) is used to adjust the depth of the disc (14) in the seed trench (8) with a seed placement device (70) positioned in the seed trench (8) for depositing a seed (71) in the seed trench (8). The seed trench (8) having been opened by the disc (14) as the work vehicle (5) moves across the ground.