Apparatus to reduce size of a light, dry, fibrous material, particularly straw, with a material supply area (1), an impeller (2) and a material release area (5) for the size reduced material as well as a ring element (4), which is arranged with a distance to the impeller (2), wherein least one size reduction tool (6) is provided at the impeller (2) and/or at the ring element (4), that is provided angular shaped, particularly L-shaped, or having the shape of a polygonal, particularly ashlar-formed, hollow profile or solid profile. Splitting particularly hard, closed fibrous structures such as nodes of straw can thereby be enabled to a major portion without excessive shortening of the straw.