Disc Harrow:
A disc harrow is a farm tool that is used to cultivate the soil where crops are to be planted. It is also used to chop up unwanted weeds or crop residues. It consists of many iron or steel discs which have a slight concavity and are arranged into two or four sections. When seen from above, the four sections would appear to form an "X" which has been flattened to be wider than it is tall. The discs are also offset so that they are not parallel with the general direction of the implement. This is so they slice the ground they cut over a little to optimize the result. The concavity of the discs as well as their offset causes them to loosen and pick up the soil they cut.