An inclined belt conveyor capable of mixing particulate material, such as agricultural seed or fertilizer. Inserting a plurality of mixing baffles into the stream of the particulate material induces a backflow of the particulate material. In the case of wet, freshly treated plant seed, this backflow causes a mixing, polishing, and drying of the plant seed. The mixing distributes the seed treatment into an even coat by rubbing the individual seeds of the seed flow stream together. The inclined belt conveyor may also be used to blend multiple varieties or types of particulate material. The mixing baffles are oriented to induce backflow and sideways lateral movement and may incorporate a passage to allow increase particulate material flow rate. The mixing baffles can selectively deploy between an angle of 20 degrees to 70 degrees to enable the mixing inclined belt conveyor to have a transfer-speed-maximizing mode and a mixing mode.