An apparatus and methods of mixing materials in a silo that includes a mixing chamber (2) with an outlet (23) the bottom and an inlet hose (4) connected to an inlet opening at the top; a sieve (16) at the top of the mixing chamber above the inlet opening and below the outlet opening to prevent contact between a particulate mixing material and the top of the mixing chamber and to allow dust through; a pump system (18) to create a negative pressure region at the top of the mixing chamber; and an air manifold assembly (8), which includes an air pressure manifold (10) having an air nozzle (12) to introduce an air stream into the mixing chamber and an air manifold cover (14) to prevent contact between the particulate mixing material and the air pressure manifold, and to allow a particulate mixed product material to pass to the mixing chamber outlet.