The invention is directed to a machine for compacting agricultural fibrous matter into a board, comprising a hopper for receiving the agricultural fibrous matter; a pre-compacting device comprising several rows of fingers configured for moving successively into, along and out of vertical slits formed in at least a wall of the hopper; an extruder comprising an extrusion passage downstream of the hopper; and a ram configured for moving in a reciprocal manner along the extrusion passage; wherein each row of fingers of the pre-compacting device is independent in speed.