An agricultural machine can include a plant processing apparatus for processing plant material. The plant processing apparatus includes a cylindrical drum rotatable about a drum axis, a rotary drive for rotating the drum about the drum axis, and a curved shell that extends around at least part of the circumference of the drum. The plant processing apparatus includes a processing channel provided between an outer surface of the cylindrical drum and an inner surface of the shell. The processing channel has an inlet end and an outlet end. Plant material is transported through the processing channel from the inlet end to the outlet end by rotation of the cylindrical drum. The drum and the shell each have sets of working elements that together process the plant material as it is fed through the processing channel.