One of the earliest of these types of devices was known as an ard.  
The number of bottoms in use at one time distinguishes the gang type of these devices from the sulky type of them.  One of the earliest of these types of devices was known as an ard.  A self-sharpening one of these devices was accidentally invented when some hot iron fell onto the cold ground at a factory owned by Robert Ransome.  One man adapted a type of Scottish saw to create a popular type of these devices from a plant in (*) Moline, Illinois.  A man employs a wheeled one of these devices in the foreground of the March image from The Very Rich Hours of the Duc de Berry.  Repeated use of these devices may create a layer known as hardpan.  These devices create trenches known as furrows and generally contain a part known as a moldboard.  A steel one of these devices was mass-manufactured by John Deere.  For 10 points, name these devices useful for loosening the soil.
The number of bottoms in use at one time distinguishes the gang type of these devices from the sulky type of them.  
plows [or ploughs]