I might as well post about some recent handiwork by my company (Vision Robotics Corp.), a robotic lettuce thinner...
When growers plant lettuce, they plant a lettuce seed every 2 to 3 inches. Ultimately, they want a lettuce plant every 10 to 12 inches. The reason for the over planting is that many of the lettuce seeds either don't come up at all, or don't survive the first couple of weeks. However, they end up with too many plants and need to thin the survivors. Except for our new, Robotic Thinner, the thinning is currently done by laborers with hoes.
Here is a link to a 30 second youtube video of it in operation:
The pictures below show the effects of thinning the lettuce. In addition to costing about 1/3 as much as manual labor using hoes to thin, notice that the ground is undisturbed by the thinner which, according to the growers using the thinner, allows the "keepers" to be more consistent in size and health since their roots are undisturbed. In addition, fewer weeds are able to get started in the unbroken ground.
In the "4 days after thinning" shot, if you look closely, you can see little brown dead lettuces that have been thinned by fertilizer in between the remaining green keepers. In the "4-5 weeks old" shot, the lettuce has been cultivated (weeded) so at this point the ground is disturbed but the lettuce is way ahead of any possible future weeds.
Each Thinner takes the place of roughly 30 to 50 people with hoes. The world (well, North America) only needs about 150 Robotic Thinners to thin all of the lettuce so it's a pretty small market. That will displace about 5,000 laborers, but it's really terrible work and the growers are having trouble getting people to do it anymore.
It's been a fun project. I know a LOT about growing and processing lettuce now.