A compost turning apparatus mountable on a loader for turning composting materials may include a mobile base having a frame with inboard, outboard, and bridging portions defining a windrow tunnel through which a windrow of composting materials are passed. The inboard portion may be configured to mount on the loader. The apparatus may include a rotor extending across the windrow tunnel, and the rotor may include a rotor shaft and paddles on the rotor shaft. A rotor drive assembly on the mobile base may rotate the rotor using a motor hydraulically-connectable to a hydraulic power system of the loader.