In a machine for ploughing parallel wall furrows there are provided spring skids (102) secured to the frame which grab between the knife-holder disk (80). Said skids (102) carry at the rear end cutting shears (106) operating in the ploughed furrow. The frame which houses the knife-holder disks (80) is spring-suspended in elevation with respect to the frame of the machine and the lateral gap of the knife-holder disks is adjustable as required. The blades (100) of the knives have a triangular configuration; they have an inclined flank and a flat extended flank. The latter forms the front edge when the tool is used in a soft ground, whereas the inclined flank forms the front edge when the tool is used in a hard ground. Seed supply conduits direct the seeds into the ploughed furrows.
