Modern grain drills operate on the same principle as the original, invented by Jethro Tull around 1700.
The grain drill consists of a succession of tubes. These have the ability to dispense the grain in the soil at the correct depth and in an array of straight rows. It also incorporates a basic metering device to feed the grain from a storage hopper into the tubes at a controlled rate. Fertilizer is frequently administered to the soil with the grain.
There is often a harrow found behind the drill so the grain can be covered as it is being sowed. The harrow is basically a frame which carries either a series of spiked teeth or groups of sharp discs that are positioned at an angle. This allows the soil to be turned and at the same time cover the grain.
Stand alone grain drills are fairly uncommon, they are usually seen as an attachment to the farm tractor.
