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. 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.
[[File:1902 Monitor seed drill detail.jpg|thumb|1902 model 12-run seed drill produced by [[Monitor Manufacturing Company]], [[Minneapolis]], [[Minnesota]].]]
''Drilling'' is the term used for the mechanized [[sowing]] of an agricultural crop. A typical seed drill consists of a hopper of seeds arranged above a series of tubes that can be set at selected distances from each other to allow optimum growth of the resulting plants. In place of a hopper most commercial seeders use an air tank which uses a fan to create a vacuum which suck grain out of the tank meters it and blows grain into the drill. Arranged in front of the tubes are a series of knife blades known as ''coulters''. In operation, the seed drill is dragged forward to allow the coulters to cut open the soil, with a metering mechanism on the hopper periodically allowing a number of seeds to fall into the tubes, and through them into the freshly cut soil. The result is a set of spaced seeding locations, which can then be covered by a built-in [[rake (tool)|rake]].
The seed drill allows farmers to sow seeds in well-spaced rows at specific depths at a specific seed rate; each tube creates a hole of a specific depth, drops in one or more seeds, and covers it over. This invention gave farmers much greater control over the depth that the seed was planted and the ability to cover the seeds without back-tracking. This greater control meant that seeds germinated consistently and in good [[soil]]. The result was an increased rate of germination, and a much-improved [[crop yield]] (up to eight times <ref>[http://www.economist.com/displaystory.cfm?story_id=E1_VPNPPGN The story of wheat | Ears of plenty | Economist.com<!-- Bot generated title -->] Paid subscription required</ref>).
A further important consideration was weed control. Broadcast seeding results in a random array of growing crops, making it difficult to control [[weed]]s using any method other than hand weeding. A field planted using a seed drill is much more uniform, typically in rows, allowing weeding with the [[Hoe (tool)|hoe]] during the course of the growing season. Weeding by hand is laborious and poor weeding limits yield.
[[Image:ChineseSeedDrill1637.jpg|thumb|[[China|Chinese]] máy gieo hạt ống đôi, công bố bởi [[Song Yingxing]] in the ''Tiangong Kaiwu'' [[encyclopedia]] of [].]]
While the [[Sumerians]] used primitive single-tube seed drills around 1500 BC, the invention never reached Europe. Multi-tube iron seed drills were invented by the Chinese in the 2nd century BC.<ref name="temple">Temple, p.25</ref> This multi-tube seed drill has been credited with giving China an efficient food production system that allowed it to support its large population for millennia.<ref name=temple /> It has been conjectured that the seed drill was introduced in Europe following contacts with China.<ref name="temple" />
The first known European seed drill was attributed to Camillo Torello and patented by the Venetian Senate in 1566. A seed drill was described in detail by Tadeo Cavalina of [[Bologna]] in 1602.<ref name="temple" /> In [[Anh]], the seed drill was further refined by [[Jethro Tull (agriculturist)|Jethro Tull]] in 1701 in the [[British Agricultural Revolution|Agricultural Revolution]]. However, seed drills of this and successive types were both expensive and unreliable, as well as fragile. Seed drills would not come into widespread use in Europe until the mid-19th century.
Over the years seed drills have become more advanced and sophisticated but the technology has remained substantially the same. The first seed drills were small enough to be drawn by a single horse but the availability of steam and, later, gasoline tractors saw the development of larger and more efficient drills that allowed farmers to seed even larger tracts in a single day. Recent improvements to drills allow seed-drilling without prior tilling. This means that soils subject to erosion or moisture loss are protected until the seed germinates and grows enough to keep the soil in place. This also helps prevent [[soil loss]] by avoiding erosion after tilling.