A combination of a semi-mounted reversible plough (10) and a seed preparation device (11) are towed behind a tractor in order to carry out a ploughing action and a seed preparation action during a single pass over the ground. The plough has a short leading towing beam (12) provided with a forward hitch (13) for coupling the plough to the rear of the tractor; a long towing beam (15) coupled with beam (12); a carrying beam (20) coupled with long towing beam (15); a cylinder operated crank mechanism (17, 18) operable to rotate towing beam (15) and carrying beam (20) as a unit about the longitudinal axis (19) of beam (15) in order to reverse the position of the plough bodies; a coupling beam (24) mounted at its forward end via a mounting beam (43) on the carrying frame (20) and towing beam (15) and projecting laterally therefrom; a swivel connector (25) at the trailing end of coupling beam (24) which is attached to the leading end of a draw bar (41) of the device (11); and a cylinder operated parallelogram linkage (24, 29). Preferably, a seed unit (34), is coupled with the seed preparation device, so that ploughing, soil preparation and seeding can take place during a single passage across a field, and the entire combination can automatically adjust itself during reversal of the plough bodies and turning of the combination in the headland.