To grow crops regularly in less-fertile areas, the soil must be turned to bring nutrients to the surface. A major advance for this type of farming was the turn plough, also known as the mould-board plough. A coulter (or skeith) could be added to cut vertically into the ground just ahead of the share (in front of the frog), a wedge-shaped cutting edge at the bottom front of the mould board with the landside of the frame supporting the under-share (below-ground component).