A seed drill sows seeds at precise intervals into a straight furrow of constant depth. It then re-covers the seeds with soil as it passes over the furrow. The seed drill consists of a seed hopper, plow and harrows, and can be pulled by a horse or tractor or pushed manually.
The seed drill was invented by Englishman Jethro Tull in 1701. Prior to its invention, farmers broadcast seed by hand, a process known as "drilling." The invention of the seed drill allowed farmers to plant seeds at constant depth and spacing, resulting in improved seed germination and crop yields. Straight rows of plants could also be cultivated mechanically much more easily than plants grown from seeds spread by hand.
Modern seed drills range in complexity, but all share the same basic parts. A plow attachment is positioned at the front of the seed drill that cuts through the earth as the drill moves forward, creating a straight furrow of constant depth. A seed hopper, generally consisting of a rotating perforated barrel or series of cups, holds a reservoir of seeds and drops them one at a time into the furrow. The harrows, mounted at the back of the seed drill, push soil back onto the seeds that sit in the furrow. This assembly can be combined in serial to create seed drills capable of planting up to 16 rows of seeds at once.