A moulboard plough - or mouldboard plough that produced a deep furrow and turned the earth after it had been cut by the coulter and shear. The moulboard was the device for guiding the plough and turning the earth over. To get the right depth for the seed the plough has to both cut and turn the earth. Moulboard ploughs were mainly used in heavy clay areas. Farmers tended to prefer wheeled ploughs on sandy soils.
They have the advantage of being able to plant seeds about 4"/10cm below the soil surface, and can also has better control over weeds by burying the "weed seeds" too deep for them to establish.