a supporting frame,

a plurality of cultivation bars which have an approximately rectilinear shape, extend along respective longitudinal axes, and are coupled to said supporting frame in order to be arranged approximately coplanar and alongside one another so as to have the respective longitudinal axes parallel to said reference axis,

mechanical spacing members, which are interleaved between the cultivation bars and are structured so that the actuation of a mechanical spacing member causes a pre-established variation of the distance transverse to said reference axis, between two adjacent cultivation bars adjacent to the actuated mechanical spacing member; said mechanical spacing members are structured so as to be operated between a first operating condition, in which the mechanical spacing member positions the two adjacent cultivation bars at a first pre-established distance one with respect to the other while keeping them mutually parallel, and a second operating condition, in which the mechanical spacing member arranges the two adjacent cultivation bars at a second pre-established distance greater than the first pre-established distance, keeping them parallel to one another;

said system being characterised in that

said mechanical spacing members comprise respective rectangular bellows-structured sheets, foldable along a folding line which extends parallel to the longitudinal axis of the bars and is approximately defined by the intersection of the respective rectangular sheet and the centre-line plane thereof.