Motion stability of an agricultural machine influences, in many respects, its working capacity and performance quality. Investigations into motion stability of agricultural machines in the system with a prime mover (a farm tractor) are of practical importance and a theoretical basis give a chance for a reasonable and matched choice of their design and technological factors and operation modes. The dependencies have been derived to analyze the motion stability of a sod seeder which consists of a frame with boxes for fertilizers and seeds and the drive elements on two support wheels. Rotary openers with a drive are mounted on the frame via a mobile spring suspension bracket. Analysis of the received dependencies shows that in order to maintain stable motion of seeders with active rotary openers, it is necessary to use special stabilizers-scarifiers. They perform additional tilling operations (loosening, slitting, moiling) and are placed behind active working elements of the machine. They create additional resistance compensating the pushing effect of rotary openers. The resistance value depends on the number, design parameters and operation modes of active working elements.