Tying unit in forage compacting machines, which being designed to form a knot (9) to join two branches (6) of a string (7) to obtain a closed-loop string structure (7), is characterized in that : - comprises at least one knot-forming device (9) including a tubular needle (3) with rotational movement having at one end a radial harpoon (8) forming an acute angle with respect to the direction of the tubular needle (3) ), inside which is lodged a main harpoon (4) with linear displacement having an end section with a recess (5) for engaging a part of the branches (6) of the rope (7) during the conformation of the knot ( 9)； wherein said end section of the main harpoon (4) is arranged in correspondence with the end of the tubular needle (3) where the radial harpoon (8) is located； - the tubular needle (3) is coupled to a moving carriage (2) with linear displacement in the same direction as the tubular needle (3)； wherein said mobile carriage (2) is coupled to a frame (1)； - further comprises a cutting device and a braking device of the two branches (6) of the rope (7) that holds the two branches (6) of the rope (7) tensioned during the forming of the knot (9) in the that said branches (6) are wound on the tubular needle (3) by hooking the radial harpoon (8) during rotation of the tubular needle (3)； where the strands (6) of the rope (7) are arranged in a direction perpendicular to the direction of the tubular needle (3) while the direction of travel of the braking device and cutting device is perpendicular to the other two directions of the tubular needle (3) and branches (6) of the rope (7)； - the cutting device and the braking device are coupled to the frame (1). (Machine-translation by Google Translate, not legally binding)1. Unidad de atado en máquinas compactadoras de forraje, que estando destinada a conformar un nudo (9) para unir dos ramales (6) de una cuerda (7) para obtener una estructura de cuerda (7) de bucle cerrado, se caracteriza porque: - comprende al menos
