Grain drill

A seed drill is a device that sows the seeds for crops by metering out the individual seeds, positioning them in the soil, and covering them to a certain average depth. The seed drill sows the seeds at equal distances and proper depth, ensuring that the seeds get covered with soil and are saved from being eaten by birds. Before the introduction of the seed drill, a common practice was to plant seeds by hand. Besides being wasteful, planting was usually imprecise and led to a poor distribution of seeds, leading to low productivity. The use of a seed drill can improve the ratio of crop yield (seeds harvested per seed planted) by as much as nine times.

Some machines for metering out seeds for planting are called planters. The concepts involved (such as mechanisms that pick up seeds from a bin and deposit them down a tube) are largely the same.

Seed drills of earlier centuries included single-tube seed drills in Sumer and multi-tube seed drills in China, and later a seed drill by Jethro Tull that was influential in the growth of farming technology in recent centuries. Even for a century after Tull, hand sowing of grain remained common.

In older methods of planting, a field is initially prepared with a plough to a series of linear cuts known as furrows. The field is then seeded by throwing the seeds over the field, a method known as manual broadcasting. In this method there will be a right depth nor proper distance. Seeds that landed in the furrows had better protection from the elements, and natural erosion or manual raking would preferentially cover them while leaving some exposed. The result was a field planted roughly in rows, but having a large number of plants outside the furrow lanes.

There are several downsides to this approach. The most obvious is that seeds that land outside the furrows will not have the growth shown by the plants sown in the furrow, since they are too shallow on the soil. Because of this, they are lost to the elements. Much of the seed remained on the surface where it never germinated or germinated prematurely, only to be killed by frost. On the surface, it was also vulnerable to being eaten by birds or carried away on the wind.

Since the furrows represent only a portion of the field's area, and broadcasting distributes seeds fairly evenly, this results in considerable wastage of seeds. Less obvious are the effects of overseeding; all crops grow best at a certain density, which varies depending on the soil and weather conditions. Additional seeding above this limit will actually reduce crop yields, in spite of more plants being sown, as there will be competition among the plants for the minerals, water and the soil available. Another reason is that the mineral resources of the soil will also deplete at a much faster rate, thereby directly affecting the growth of the plants.

...
Wikipedia