An agricultural tool assembly (21) disclosed is usable on a variety of implements in place of shovels, blades, tines or sweeps and on novel cultivating or crop root undercutting implements and the like. Assembly (21) includes a rotary disk (23) mounted on a lower end of a rotary spindle (25). An offset mount for the spindle includes a shank (41) adapted to be received in the vertical slot of a clamp (22) and a sleeve (45) offset from the shank for rotatably supporting the spindle. The sleeve is connected to the shank, using a bifurcated portion comprised of spaced plates (47, 48) connected to the sleeve with a lower pivot member (52) and an upper fastener (58) extending through arcuate slots (61 and 62) in the spaced plates. The disk may be tilted at a selected angle or set horizontally and for some applications may be set to release in the event the blade strikes an obstruction. A cultivator implement has front and rear disk gangs (108, 109, 114, 115) and a rear centered tool assembly (21). An onion undercutting implement has a front tool bar (134) with front tool assemblies (121a, 121b and 121c) clamped thereto and a rear tool bar (135) with rear tool assemblies (122a, 122b and 122c) clamped thereto. A planter attachment has a support frame that disposes a tool assembly (21) ahead of the planter (230) to cut the old crop prior to have the planter deposit the seed.